Block 4 - development Flashcards
1
Q
define growth
A
increase in size that doesn’t imply development
2
Q
what is development
A
change with time involving:
morphogenesis - development of shape or form
differentiation - specialisation of function
both are independent of growth
3
Q
what is embryogenesis
A
it occurs in animals and plants and is where the zygote starts to undergo differentiation and morphogenesis to produce rudimentary structures of the adult
4
Q
describe the embryonic development of the zebra fish
A
it takes ~40hrs. ordered cell divisions produce various structures of the zebra fish. single cell zygote –> zygote change –> acquired polarity –> first cell division is uneven. this is followed by further divisions and morphogenesis
5
Q
what is cell polarity
A
acquisition of asymmetry which determines subsequent cell division and fate
6
Q
why is there a clear difference between the animal and vegetal pole of amphibians
A
because there is a difference in pigment
7
Q
what happens to the algal zygote upon polarity change
A
it goes from spherical to pear
8
Q
describe the development of multicellularity in the starfish
A
unfertilized egg –> 2 cell stage –> 4 cell stage –> 16 cell stage –> 32 cell stage
9
Q
what does organogenesis ensure
A
that all the correct structures are produced in the right place at the right time
10
Q
differentiation works in parallel with ……….
A
morphogenesis
11
Q
cell ………… and …………….. are important in morphogenesis
A
movement
adhesion
12
Q
differentiation is usually due to switching on sets of ….. when a particular cell type becomes established
A
genes
gene expression is a key control in development
13
Q
what method allows visualisation of protein complexes inside of cells
A
EM methods
14
Q
what is the forward genetics approach
A
create mutants and isolate, identify the gene that has become mutated, draw conclusion on gene function based on mutant function
15
Q
what is a homeotic mutation
A
affects specification of organ type
16
Q
what are 6 advantages of model organisms for genetics
A
- small and easy to grow
- rapid generation time
- lots of progeny
- preferably self fertile and able to be crossed
- easy to produce mutants
- multiple people working on it
17
Q
what 3 advantages of model organisms for molecular biology
A
- small genome - enables full sequencing and gene isolation
- easy to genetically transform
- methods for isolating genes corresponding to mutants
18
Q
what is the genome
A
the amount of DNA in the haploid form of the organism
19
Q
describe c. elegans
A
small bacterivorous nematode simple development usually self fertilising hermaphrodites 3 day life cycle easy to manipulate short generation time lots of progeny each gender has exactly the same number of cells genome fully sequenced
20
Q
describe drosophila
A
male and female flies 2 week life cycle easy to mutate learned a lot about pattern formation and morphogenesis from them genome fully sequenced
21
Q
describe Arabidopsis
A
small flowering plant self and cross fertile 6 weeks life cycle genome fully sequenced easy to produce mutants small genome short generation time for a plant
22
Q
what is fucus
A
brown algae
23
Q
describe the early development of the fucus zygote
A
- after fertilisation of the males and female gametes the zygote is immediately apolar
- after 12hrs asymmetry develops
- 15hrs - germinating rhizoid
- 24hrs - first asymmetric division (right angles to the axis of symmetry). the lower cell produces the rhizoid which anchors the plant to the rocks. the upper cell divides further and develops into the thallus
24
Q
on which side of the fucus plant does the rhizoid develop
A
the shaded side
25
the rhizoid appears at 12 hrs in the fucus. how and up to what point can the axis of polarity be changed
we can change the axis of polarity up to 10hrs
26
what determines polarity of the fucus - what factors affect it
fertilization (rhizoid at entry point)
heat (rhizoid develops at warm side)
pH and salt (rhizoid to alkaline pH and salt)
electrical gradient (rhizoid at -ve pole)
27
development of polarity is accompanied by production of ..………….. ………….. which generate an electrical potential
ionic gradients
28
how is calcium involved in fucus development
- disruption of Ca gradients prevents polarity development
- localisation of Ca channels is observed after 5-6hrs illumination
- there is a Ca influx at the rhizoid end and efflux at the other end. initially Ca channels are evenly distributed but they become localised at the rhizoid end when polarity develops
29
why are some zygotes already polar upon fertilization
it is often due to egg cell gamete
30
what are localised cytoplasmic determinants
they are components in the cytoplasm that affect cell fate
31
how can we show that a component has an effect on development
we need to demonstrate its action e.g. removal or translocation
32
describe the ascidian regions of coloured cytoplasm
ascidian egg has regions of cytoplasm with different coloured inclusions that are linked to cell fate. pigmentation doesn't control development but is localised in regions that have components that do control development. the cytoplasm contains localised cytoplasmic determinants
33
what is a downfall of fucus and ascidians as model organisms
neither of them allow easy mutant formation
34
in drosophila how is anterior-posterior polarity established
it is established in the eggs
35
why are body segments important in drosophila
they are important for producing organs
36
what is the egg precursor
oocyte
37
what is the roles of nurse cells
they synthesise macromolecules in the ovary that are transported to the oocyte as it develops via cytoplasmic bridges. some macromolecules become asymmetrically distributed
38
describe the drosophila bicoid mutant
the embryo lacks the head and thorax at the anterior end and instead has a second set of posterior structures. it is a single gene mutation. the phenotype can be rescued by injecting WT bicoid mRNA in the anterior end
39
what is the WT bicoid gene product required for
normal anterior development of the embryo. the bicoid mRNA/protein are localised at the anterior. mRNA is asymmetrically distributed so the protein accumulates the same
40
bicoid mRNA/protein is synthesised in the nurse cells and transferred to the oocyte
mRNA
41
bicoid localisation is established during oocyte development in the …………. …………….
maternal ovary
42
what is a maternal effect gene
when the female is responsible for expression of the phenotype of the developing embryo
43
what are other maternal effect genes involved in determining anterior-posterior polarity in drosophila
bicoid and hunchback regulate production of anterior structures
nanos and caudal regulate production of posterior structures
44
bicoid, hunchback and caudal are …. that regulate other genes controlling later steps in development
TFs
45
polar distribution of bicoid and nanos mRNA is established in the ………...
ovary
46
describe the role of bicoid and nanos in drosophila development
bicoid and nanos are localised and translationally regulate hunchback and caudal bicoid inhibits translation of caudal mRNA at the anterior pole, resulting in accumulation of caudal towards the posterior. nanos inhibits translation of hunchback mRNA at the posterior so it accumulates at the anterior
47
describe the distribution of bicoid, nanos, caudal, and hunchback mRNA in drosophila and compare it to the protein distribution
mRNA - bicoid at the anterior and nanos at the posterior
hunchback and caudal throughout
protein - hunchback and bicoid at anterior and nanos and caudal at posterior
48
what is the cytoskeleton
an intracellular network of protein filaments of several types - microtubules, actin filaments and intermediate filaments
49
list some developmental aspects involving the cytoskeleton
```
acquisition of polarity
control of cell size and shape
control of cell division
intracellular movement of components
cell movement and adhesion
```
50
describe microtubules structure
- composed of alpha and beta tubulin dimers
- both subunits bind GTP
- only GTP bound to beta tubulin can be hydrolysed to GDP
- they consist of 13 protofilaments each of which is a polymer of tubulin dimers
- they are relatively big structures
- they undergo continual disassembly and assembly regulated by GTP
- tubulin dimers bound to GTP are added to the plus end of the microtubule. tubulin dimers are lost from the minus end
51
what is the microtubule GTP cap
it is at the plus end where both subunits of the dimer are bound to GTP
52
going down the microtubule, ……….. hydrolyses on …… subunits and dimers bound to GDP are lost at the ……. end
GTP
beta
minus
53
what happens to microtubules if [tubulin-GTP] is low
the rate of addition at the plus end is low and GTP hydrolysis will remove the GTP cap. Tubulin is rapidly lost from the plus end resulting in complete depolymerisation.
54
whether a microtubule grows or shrinks is dependent on what
[tubulin-GTP]
high --> microtubule growth
low --> microtubule depolymerisation
55
how can disassembly be seen in microtubules
frayed ends
56
what is the MTOC and how is it different in plants and animals
where microtubules assemble and radiate. in animal cells it is the centrosome which contains 2 centrioles. plants don't have centrosome MTOC, instead they control polymerisation with local ion concentrations
57
what is microtubule stability affected by
low temperature causes depolymerisation
| regulated by MAPs - proteins that interact with microtubules e.g. tam
58
mitosis spindle is made of ……………. - they move chromosomes. microtubules are also involved in movement of …………. and ………….
microtubules
| vesicles and organelles
59
describe the process of movement along microtubules
it involved motor proteins kinesin and dynein which use ATP hydrolysis to move components to the plus or minus end of the microtubules
- kinesin moves cargo --> +end. it binds to the receptor protein on the vesicle and also to the microtubules. dynein works in the same way but instead moves cargo to the minus end
60
describe the structure of actin microfilaments
- actin assembles as a filament but is not as large or as complex as microtubules
- the globular actin monomer is called G-actin and it polymerises into F-actin filaments which can be dimers or trimers and are added to the growing filament
- the filaments consist of tightly wound helix
- actin binds ATP or ADP and hydrolysis of ATP follows polymerisation. monomers are added mainly at the + end. monomers bound to ADP are lost from the minus end
61
what is the effect of cytochalasin B on actin microfilaments
it binds at the + end preventing elongation
62
what proteins can bind to actin and regulate polymerisation and depolymerisation
- cofilin promotes disassociation from the - end
- profilin promotes ATP binding to actin and polymerisation
- Arp2/3 proteins act as nucleation sites to stimulate assembly of new filaments
63
actin filaments can assemble as ………… or ……………… but what is the difference between these
bundles
networks
they have different types of cross-linking protein
the bundle is a string or parallel filaments of actin and is very strong
the network has looser cross-linking resembling chicken wire
64
describe the structure of intermediate filaments
- they are strong but not dynamic
- they associate with the PM and organelles
- they are composed of various types of proteins
- different filaments have the same basic structure N-head-rod-tail-C
- there are no +/- ends, assembly involves multimerization
- they are more stable than microtubules and microfilaments
- they make dimer and tetrameric structures that are assembled into the protofilament --> filament
- they associate with other cytoskeletal elements, the PM and organelles and help to increase mechanical strength and anchor components
65
what parts of the cytoskeleton are particularly important for controlling cell shape and explain their role
microtubules and actin filaments
66
explain the role of microfilaments in controlling cell shape
actin bundles/networks underlie and support the PM. the actin networks is connected to spectrin cross-linking protein and anchored to the PM by erythrocyte ankyrin (actin network makes shape and PM is spread over it)
actin bundles support microvilli of intestinal epithelial cells
67
actin microfilaments also have a role in ………… ………… in plants. several mutants in ………… …………. lack ……….. proteins required for normal actin filament production
trichome development
trichome development
Arp2/3
68
which components of the cytoskeleton are important in controlling intracellular movement
microtubules and microfilaments
69
using the bicoid examples explain why intracellular movement is critical in development and the role of the cytoskeleton
bicoid is synthesised in the nurse cells and transferred to the oocyte where it becomes localised at the anterior end. this movement is prevented by drugs that inhibit tubulin polymerisation. localisation requires mRNA binding to microtubules via linker proteins. mRNA protein complexes move along the microtubules bound to kinesin motor proteins
70
what is the cell cycle
the process that cells undergo to duplicate their contents to pass onto two identical daughter cells (mitotic). this involves both DNA replication and duplication of cellular constituents and their separation into 2 daughter cells (cell replication + cell division (cytokinesis))
71
in which is the cell cycle more complicated, eukaryotes or prokaryotes
eukaryotes
72
describe the prokaryotic cell cycle
- takes 20-40 mins in e.coli
- bacteria have circular DNA molecules
- cellular growth and DNA replication are continuous throughout the cell cycle
73
describe prokaryotic DNA synthesis
1. cleavage of DNA to produce 3' end
2. synthesis of RNA primer for DNA pol to allow DNA to be primed for creation of the complementary strand
Other proteins are required e.g. type II
as the cell gets bigger the DNA is replicated. when the cell reaches a certain size it divides into 2
74
cells with 2 copies or no copies of DNA …….
die
75
describe the eukaryotic cell cycle
- takes longer - yeast 2hrs, humans 24 hrs - because the cellular constituents are much more complicated and the process is more complex to ensure production of 2 identical daughter cells
- S phase - DNA replication occurs - NOT continuous
- G phases - both contain crucial checkpoints
- M phase - replicated chromosomes are separated into 2 daughter cells
- cytokinesis - process by which the 2 cells separate
76
during mitosis chromosomes are condensed/decondensed
| during interphase, chromosomes are condensed/decondensed
condensed
| decondensed
77
how do we know the eukaryotic cell cycle is a well conserved process
proteins from yeast and humans are interchangeable
78
describe eukaryotic DNA synthesis
- larger genome than prokaryotes s is more complicated
- the ORC (origin or replication complex) is a complex of proteins which bind to DNA at specific sequences and have many roles in replicating DNA. they bind to DNA in the S phase and are stimulated to cause the replication of DNA. the cell coordinates this so that replication only occurs in the S phase
79
how is the ORC regulated
it is regulated by CDKs which bind to and activate the ORC which stimulates DNA replication in the S phase
80
what is mitosis and when does it occur
chromosome separation after the G2 phase
81
what are the 4 steps of mitosis
prophase, metaphase, anaphase and telophase
82
what is the product of mitosis
2 diploid cells
83
what happens in prophase
centrioles duplicate, centrioles move to poles, mitotic spindle forms
84
what happens in metaphase
chromosomes move to the equator of the cell forming the metaphase plate
85
what happens in anaphase
duplicated chromosomes split and move to opposite poles
86
what happens in telophase
nuclear membrane reforms around the chromosomes at each of the poles. nuclei reform and the cell divides
87
how can decondensed DNA in interphase be seen
if tagged with GFP
88
what is the first step in allowing mitosis to occur
condensation of chromosomes
89
describe the process of cytokinesis/abscission
- constriction forms and separates the cells
- contractile ring is made from actin microfilaments and it constricts the equator between the forming cells
- abscission bridge forms and gets longer until we get a snap and a break which physically separates the cells
actin ring --> constriction --> abscission bridge --> physical separation
90
why do we need redundancy in the cell cycle
if one mechanism goes wrong another one can compensate - belts and braces
91
what are the 3 levels of control in the cell cycle
1. transcription - gene expression
2. protein level and stability
3. protein activity - post translational modifications e.g. phosphorylation
they all work in parallel and allow for redundancy
92
give the sequence of a start codon
ATG
93
give the sequence of a stop codon
TAA
94
what are the 2 types of transcription
- general gene expression - where the gene is transcribed constitutively e.g. housekeeping genes - expression not regulated at all. RNA pol binds to the TATA box in the promotor to produce mRNA. RNA pol is not regulated, it is just constitutively active-
- specific gene expression - genes are only transcribed at a certain time/place. there is a more complicated promoter and extra TFs. RNA pol still binds to the TATA box. the enhancer is bound by a TF that stimulates RNA pol activity to create RNA but only at specific times (2 TFs control gene expression at particular times/places)
95
describe the fission yeast
unicellular eukaryote that is easy to grow in the lab and is used to study the cell cycle. good model organism. there is huge conservation of controls between yeast and humans.
96
are all the genes involved in the cell cycle expressed at the same time
no, different genes are expressed at different cell cycle times
97
what is the role of the MBF TF and MCB
they regulate gene expression at the end of G1/start of S phase
98
what is the outcome of MBF TF binding to MCB
the MBF complex binds to MCB enhancer DNNA sequence in the promotor and stimulates RNA pol to drive gene expression exclusively during the S phase. there are at least 20 yeast genes controlled like this. in each case there is an MCB with a simple motif: ACGCG. wherever an MCB is, that gene is expressed in the S phase because the sequence is bound by MBF
99
give 3 examples of S phase genes and their roles
cdc22+ - encodes ribonucleotide reductase, essential for making DNA
cdc18+ - encodes an important part of the ORC
cig2+ - G1 cyclin which has an important roles in regulating genes for the cell cycle and is important in controlling progression
100
mRNA is unstable and almost immediately …………., so we see fluctuation in the cell cycle of mRNA and protein
degraded
101
what is transcriptional control important for
cell cycle control
| cell economy
102
describe the process of entering S phase from G1
cells don't enter the S phase unless MBF is active. MBF = E2F in humans. E2F interacts with P53 and Rb and regulates gene expression at the start of S phase like MBF
103
how are ubiquination and the proteasome involved in regulating protein levels and stability
ubiquination causes specific degradation of protein through the proteasome.
104
why is it important that more stable proteins have a mechanism of being removed
because we would get a stepwise increase if they weren't removed
105
what is the relationship between CDK1 and cyclin B
CDK1 (stable) is a master controller of the cell cycle and its activity is regulated by binding to the cyclin B molecule (unstable). CDK1 is inactive unless bound to cyclin B. binding to cyclin B is crucial for cell cycle progression from G2 --> M (allowed by active CDK1. to exit M CDK1 needs to be inactivated again by cyclin B being ubiquinated and targeted to the proteasome leaving inactivated CDK1
106
in order to activate CDK1 it needs to be bound by cyclin B but what else must also happen
it must be dephosphorylated - modifies protein activity
107
what are cell cycle checkpoints
surveillance mechanisms that ensure the cell cycle doesn't progress until the previous stage has been completed. they can stop the cell cycle to allow repair mechanisms. checkpoint is only active when there is damage
108
what is the role of the G2 checkpoint
ensure M only occurs after S is complete. a defect in S results in the G2 checkpoint stopping the cell cycle
109
defective checkpoints are seen in many …………….
cancers
110
what happens when the checkpoint becomes activated
when the checkpoint is active due to damage, we see CDK1 inactivation by phosphorylation which leads to a delay in G2 to allow DNA repair then the cell cycle resumes when CDK1 is reactivated after the repair is complete
111
what is likely to result if damaged DNA enters the M phase
cancer
112
what is the epidermis
outer single cell layer covering the organs of the plant
113
what are the 3 cells types of the leaf epidermis and give a short description of each
- pavement cells - undifferentiated/uncommitted epidermal cells
- stomatal guard cells - can swell/shrink
- trichomes - single branched cells projecting from the surface
114
are differentiated cells distributed evenly across the surface of the epidermis
reasonably evenly
115
describe root epidermal cells
there are hair cells and non-hair cells - root hairs are single cells that project from the root epidermis
116
describe seed epidermal cells
no differentiation of cell type
| biosynthetic activity to make brown pigments that accumulate in the seed coat
117
how do we identify genes controlling epidermal cell fate
use forward genetic approach
118
what are common phenotypes of trichome mutants - how many genes have been identified to be involved in trichome development
altered in number, distribution or morphology of trichomes
| 25 genes can mutate and alter trichome development
119
describe the gl1 and ttg1 mutants and compare to WT
they have no trichomes. the WT genes are required for commitment of a leaf epidermal cell to differentiate into a trichome i.e. they are regulators of epidermal cell fate
120
what is the gl1 gene product
it is a TF that switches on genes to express trichomes
121
what is the ttg1 gene product
it is a protein that bind to GL1 and is required for GL1 action
122
describe gl3 mutants and the WT function
they have fewer trichomes than WT, so WT GL3 protein regulates trichome cell fate. GL3 is a TF that forms a protein complex with TTG1 and GL1.
123
describe the GL3, GL1 and TTG1 complex
the complex is a positive regulator that switches on genes in the trichome differential pathway. target genes include other TFs
complex --> target genes --> trichomes
124
why does the GL3 mutant still have some trichomes
there are other genes that have proteins similar to GL3. when GL3 is mutated, these proteins can take over the function - functional redundancy. the same function is carried out but not as well
125
what is the outcome when the GL3, GL1 and TTG1 complex is overexpressed
we see overproduction of trichomes
126
what happens if GL3 is overexpressed
there is more positive regulator and the transgenic plants are very hairy because there is more epidermal commitment to trichomes
127
what other signal do cells that commit to form trichomes produce
signals that repress trichome formation in adjacent cells i.e. negative regulators
128
describe triptychon and caprice mutants
they lack repressive signal that prevents trichome clustering
129
what are TRY and CPC
they are TFs that cause repression of trichomes
130
what is the number of trichomes on the surface of the leaf a compromise between
positive and negative signal
131
describe dis mutants
they have abnormal trichome morphology
132
the genes for morphogenesis function upstream/downstream of commitment genes
downstream
133
crossing mutants altered in commitment and morphogenesis results in …………..
epistasis
134
the genes altered in commitment ………… the effect of the genes in downstream morphogenesis
override
135
what is the phenotype of the gl1 and dis1 double mutant and provide an explanation
no trichomes - gl1 is epistatic to dis1. GL1 functions before DIS1 morphogenesis in the trichome differentiation pathway
136
of 2 genes the epistatic gene normally comes first/second in the pathway
first
137
are stomata evenly spaced over the leaf epidermis
yes
138
what are speechless, mute and fama
they are 3 TFs that control steps in stomatal formation - speechless initiates stomatal morphogenesis (commitment)
- mute and fama control later steps in stomatal development
139
describe the tmm mutant and the inferred WT function
it has clusters of stomata so WT controls spatial distribution of stomatal production
140
are mutants of stomatal development altered in trichome function
no, and trichome mutants are not altered in stomatal development. fates of leaf trichome and stomatal cells are controlled independently
141
in contrast to leaf hairs, root hairs arise in a ………... dependent manner
position
142
describe the commitment of a cells to become a root hair
we need positive regulators to commit epidermal cells to make root hairs. hair cells arise at junctions between adjacent cortical cells (under the epidermal cells). positional information is transmitted from the cortical cells to the epidermal cells. the positional and positive signals work together to produce hair
143
the root has files of ………… and …….-...……. cells
hair
| non-hair
144
where are cortical cells found
under the epidermal cells
145
describe the wer mutant and its inferred WT function
it shows ectopic root hair production - produces hair from non-hair cells. WT wer represses hair formation in non-hair cells i.e. it specifies non hair cell fate
146
what is the wer gene product
it encodes a TF and is expressed in non hair cells to switch on a gene that produces a repressor of hair production
WER --> repressor --I hair (non-hair cell)
147
other than the wer mutant, what other mutant has ectopic root hair production and what does this indicate about its function
ttg1 mutant - therefore ttg1 like wer specifies non-hair cell fate.
148
describe how wer/ttg1 are involved in root hair production
non hair cells produce a signal that represses the action of wer/ttg1 in adjacent cells. also a signal from cortical cells inhibits wer expression in hair cells - positional information.
non hair cell: wer/ttg1 --> repressor --I hair
hair cell: signal from non hair cell and cortical cells prevents production of the repressor so we get hair
in non hair cells, if either of wer/ttg1 is mutated we don't get the repressor and we get hair production
(see diagram)
149
list the 3 types of epidermis that ttg1 works in
leaf, root and seed
150
how is ttg1 involved in the seed epidermis
ttg1 associates with TFs to control synthesis of the brown pigments called condensed tannins. ttg1 mutant doesn't make brown pigment so WT is required for the pigment biosynthesis. ttg1 facilitates the action of TFs, without this we don't get brown pigment
151
what are the 2 initial steps in morphogenesis and give a short explanation of both
- acquisition of polarity - (sometimes already established in the female gamete) - involves spatial distribution of regulatory factors i.e. localised cytoplasmic determinants that control morphogenesis
- pattern formation - development of structure, shape and form but in a predictable pattern manner
152
in drosophila, pattern formation in the embryo results from sequential expression and action of sets of ………… Expression of …………. …………. ………… establishes gradients of TF distribution in the oocyte. Cascade of TF activities determines pattern formation
TFs
| maternal effect genes
153
explain how the initial distribution of TFs in the embryo determines subsequent events
the pattern of TF activity leads to production of body segments (14 body segments).expression of TFs in the segments determines segment specific patterns of organ formation, pigmentation etc
maternal affects genes --> segmentation genes --> 14 segments --> organs
154
what are the precursors of body segments
14 parasegments
155
what are the 3 types of segmentation gene and how do they interact with each other
gap genes regulate expression of pair-rule genes, which regulate segment polarity genes
156
describe the distribution of gap gene, kruppel
expressed in broad transverse band covering a number off different parasegments as a result of the distribution of bicoid, hunchback, nanos and caudal TFs. distribution of maternal effect proteins that positively/negatively regulate kruppel transcription determine the pattern of expression
157
how are other gap genes switched on
by other relative concentrations of TFs, so, in different positions along the developing embryo
158
what is Kruppel and describe the mutant phenotype in drosophila
it is a TF that regulates pair rule genes. the mutant lacks series of segments as pair rule genes are not switched on which leads to abnormalities in the mature fly
159
give 2 examples of pair rule genes and describe their expression distribution along with the mutant phenotype
even skipped (eve) (odd numbered parasegments)
fushi-tarazu (ftz) (even numbered parasegments)
they are both expressed in 7 stripes. the expression is dependent on gap genes TF giving positive/negative effects on transcription.
eve and ftz both regulate segment polarity genes.
the mutants lack parts of segments which alters pattern formation in the mature fly
160
give an example of a segment polarity gene and describe the pattern of expression
engrailed gene - expressed in 14 stripes (in every parasegment). the pattern of expression is determined by the pair rule genes TFs
161
describe the ftz mutant in terms of the segment polarity genes
the ftz mutant doesn't express engrailed in even numbered parasegments.
162
describe mutants of engrailed
they have duplications or defects in each segment which leads to abnormalities in the mature fly
163
what do segment polarity genes ultimately regulate
morphogenesis of segments - organ formation - further TFs control the cascade
164
describe the cells movement in the blastocoel
cell movement occurs in the blastocoel to rearrange the cells as we get gastrulation
165
describe the developmental steps from zygote to gastrula
zygote (cleavage) --> 8 cell stage (cleavage) --> blastula (morphogenesis) --> gastrulation (invagination) --> gastrula
166
what are the germ layers of the gastrula
endoderm
mesoderm
ectoderm
(the gastrula also contains the blastopore and the blastocoel)
167
cells in the blastocoel rearrange by ……………. to form embryonic tissue layers during gastrulation
migration
168
compare morphogenesis of plants and animals
both have commitment of cells and TF cascades in pattern formation
adjacent plant cells are fixed together via their walls. therefore,, cell movement and migration isn't a feature of plant morphogenesis. instead plant morphogenesis involves:
- control of which cells undergo division
- control of orientation of plane of division
- control of direction and extent of cell expansion
169
how is the cytoskeleton involved in plant cell division
the cytoskeleton regulates the plane of division through the pre-prophase band of microtubules. the ppb disappears and the microtubules reappear in the spindle. normal mitosis occurs and the chromosomes move to the poles of the cell and the microtubules reorganise into the phragmoplast. the phragmoplast microtubules then assemble the PM and cells wall (they recruit the cell plate - developing cell wall)
170
what is the pre-prophase band of microtubules
a band of microtubules that marks the orientation of the plane of cell division
171
why is the plane of division not always regulated
because it is not important in all cells
172
what is the phragmoplast
an accumulation of microtubules which marks the original position of the ppb
173
in plants the plane of division is pre-determined by …...
ppb
174
why are ppb not found in animal cells
because animal cells can divide and move around so there is much less requirement to control the plane of division
175
a committed leaf epidermal cell divides …………. (controlled by ………) to produce a small cell (…………..) that will divide further to produce the ………. ……. ……… and adjacent cells. the GMC divides longitudinally (………….) to form the ……. ……. The other cell divides and produces daughter cells that will be next to the ………. ……….. ……...
```
asymmetrically
ppb
meristemoid
guard mother cell
symmetrically
guard cells
stomatal guard cell
```
176
what is the function of speechless in stomatal development
TF required for initial commitment to produce meristemoid
177
what is the function of mute in stomatal development
TF that controls generation of GMC from the meristemoid
178
what is the function of fama in stomatal development
TF that regulates GMC cell division
179
describe the process in developing a root hair
root hair committed cells show localised cell wall weakening followed by localised outgrowth of the PM, deposition of new cell wall material and nuclear migration into the hair. cell expansion is contributing to morphogenesis because root hairs alter morphogenesis
180
control of which 2 processes in particular is important in root hair development
control of direction and extent of cell expansion
181
what factors can affect root hair development
- low pH stimulates cell wall loosening by activating expansins that break bonds between polysaccharides
- auxin stimulates acidification and hence expansion (activates H+ pumps through gene expression
182
describe the process of auxin and GA extension growth
- unidirectional light causes phototropism (growth towards light). this involves auxin accumulating on the shaded side --> differential growth --> bend
- photoreceptors suppress extension through the activity of growth regulators like auxin in response to light
- auxin and GA promote extension. GA overcomes DELLA proteins that repress extension by inhibiting growth promoting TFs. light promotes an increase in DELLAs and GA destruction. Binding of GA to its receptor (G1D1) enables it to interact with DELLA proteins causing them to be targeted for proteolytic destruction. in the absence of light GA gets rid of DELLA to allow extension
183
in drosophila, at the end of embryo development, we have all the components to make the adult fly. what is different compared to this in plants
in plants we end up with a very rudimentary structure. we see cotyledons, a stem and a rudimentary root and all the organs are produced subsequently
184
what are meristems
small groups of dividing cells which produce most of the cells of the organism. they are found at the root/shoot apex as root/shoot apical meristems. meristems contain stem cells in a perpetuated undifferentiated state and have the capacity to produce new cells of the organism. they don't differentiate but divide into cells that do.
185
other than the root/shoot apical meristems what other type of meristems are there
lateral meristems which give rise to branches
186
what are the 2 tissue types of the shoot meristem and give a short description of each
tunica - 2 layers of cells that cover the dome of the meristem (growing as the meristem and shoot grow
corpus - below the tunica and contains stem cells
187
anticlinal divisions are found in the tunica layers of the shoot meristem. describe these divisions
the divisions are at right angles to the surface so we are gradually increasing the cell number that is covering the dome
188
what kind of divisions are seen in the corpus of the shoot meristem
anticlinal and periclinal. anticlinal increases width and periclinal increase length of the meristematic region
189
what happens spatially when cells divide in the meristem to allow the meristem to produce leaves
they are pushed laterally to produce a region of cell division which can give rise to leaf structures. we get production of leaf primordia
190
describe the process of leaf formation from shoot meristems and how they form in the correct spatial orientation (organogenesis)
- leaf primordia develop laterally from the shoot apical
- leaf primordia divides and expands to produce the different tissues of the leaf
- there is positional information in the meristem to ensure that leaf primordia are produced in the right positions (spiral arrangement of leaf primordia)
191
what is phyllotaxy
it is the arrangement of leaves around the apex (genetically determined)
192
define the L1, L1, CZ, PZ and RZ zones of the meristem
L! and L2 layers are the tunica which covers the shoot apical meristem
CZ is the central zone in the corpus where the SC are
PZ is the peripheral zone
RZ is the rib zone
193
what happens in the meristem when SCs divide
when the CZ SCs divide they produce daughter cells both laterally and below. lateral cells go into the PZ and the cells below go into the rib zone. the cells start to differentiate in the PZ and RZ.
194
how are SCs defined and how is the SC population in the meristem maintained
stem cells are defined by their position in the meristem (any cell in the CZ will be a SC, if the CZ size changes so would the size of the SC population. the population is maintained by wus - it regulates genes that regulate SC
195
what is the phenotype of wuschel gene mutants
they lack functional SCs. it has cotyledons and a rudimentary stem and root but fails to differentiate other organs
196
what is the WT function of the wus gene
it encodes a TF expressed just below the CZ. it is essential to generate the SC population and maintain the SC. it regulates genes that regulate SC. wus induces expression of genes characteristic of SC (positive regulator of SCs)
197
what is CLAVATA3
stem cell gene expressed in the CZ where the SC are located
198
describe the phenotypes of CLAVATA 1,2,3 mutants and the inferred WT function of the CLV genes
they have enlarged meristems because they accumulate SC, so CLV genes control SC population size (negatively regulate size). wus expression is also expanded in mutants of CLV so CLV must suppress wus in the WT
199
describe the relationship between SC and wus that controls SC population
SC negatively regulate wus and wus positively regulates SC. the size of the population is controlled by the balance of positive signals from the organizing centre to the SC and negative feedback from the SC to the organising centre
200
how do we know that the organising centre specifies formation of the SCs
wus is expressed before CLV3 expression appears
201
what maintains the SC population in the seedling
wus/CLV relationship
202
describe the basic process of the reproductive transition at the shoot apex
vegetative meristem --> inflorescence meristem --> each produce a single flower
- vegetative shoot receives signals to convert to a reproductive meristem. it stops producing leaves and starts producing inflorescences. inflorescence meristem grows and laterally produces floral meristems, each of which produces a flower
203
what are inflorescences
structures that bear flowers
204
describe the phenotype of lfy mutants and the inferred WT function
they have partial conversion of floral meristems into vegetative meristems so the WT promotes floral meristem identity
205
what is antirrhinum majus
it is a plant used to study floral development and mutations are generated by movement of transposable elements
206
what is a transposable element
piece of DNA which copies itself and excises out of the genome and potentially re-excises elsewhere in the genome. they encode transposase (which cuts the TE borders). we can speed up the TE movement by moving plants to a lower temperature
207
describe the phenotype of the antirrhinum majus flo mutant and the inferred function of the WT gene
flo mutant shows conversion of floral meristems to vegetative meristems, so WT flo is involved in promoting floral meristem identity, similar to lfy in Arabidopsis
208
what are the 4 organs of the flower
each floral meristem produces the appropriate number/type of floral organs in the correct positions. organs:
- sepal (form flower buds)
- inside the sepals are the petals
- inside the petals are the stamens (male organs)
- in the centre is the carpel (female organ)
209
how are the flower organs organised
in 4 whirls
210
describe the Arabidopsis apetela 3 mutants
single gene mutant - no petals or stamens
| lacks gene B
211
describe the Arabidopsis agamous mutant
single gene mutation - no male or female organs but lots (more than WT) of petals and sepals
lacks gene C
the mutant terminates floral meristem activity by inhibiting wus. without wus there is no SC production and no organ formation
212
what type of mutations are the apetela and agamous mutations classed as
homeotic mutations
213
what are homeotic mutations
they result in the incorrect positioning and number of organs
214
describe the ABC model for flower morphogenesis
- it was created by studying mutants
- 3 genes - A, B and C all encode TFs that regulate floral organ genes
- outermost whirl - A - specifies sepals
- second whirl - A and B - specifies petals
- third whirl - B and C - specifies stamens
- fourth whirl - C only - specifies carpels
215
what happens when a plant lacks expression of gene C
expression of gene C inhibits gene A and vice versa. by lacking C, A can now be expressed in all whirls. we get more petals from whirl 3 because A is expressed instead of C and the same thing happens in the 4th whirl and we get extra sepals
216
C provides a stop signal for floral organ production, what does this mean for C mutants
in a C mutant there is no stop signal in the 4th whirl and the floral meristem keeps producing floral organs and the only ones it can produce are sepals and petals which are produced indefinitely
217
what is the phenotype of plant mutants lacking A
they only have carpels and stamens
218
describe the pattern of expression of A, B and C flower genes
they are expressed in the expected pattern of localisation from the ABC model
219
morphogenesis in plants works through …...…….
| meristems determine the pattern of expression of genes which determines ……………. formation
meristems
| organ
220
what is the difference between morphogenesis in plants and animals
animals - TF cascade --> segments
| plants - involves meristems and TF cascade
221
give an examples of a protein hormone
insulin
222
give an example of a peptide hormone
ADH
223
give 2 examples of steroid hormones
estradiol and testosterone
224
what is adhesion
when we combine sticking with signalling - selective
225
what is juxtacrine signalling
when the receptor and ligand are brought together by contact
226
what is the cause of Alzheimer's and how does it come about
gamma secretase is involved in proteolytic cleavage of the amyloid beta precursor protein, creating the AB peptide, believed to be the causative agent of Alzheimer's
227
what kind of body plan does c.elegans have
tripoblastic
228
where are the c.elegans gonads
between the body wall muscle layer and the intestine
229
why is it useful that c.elegans are transparent
we can see all cell divisions and kill individual cells with lasers
230
what is the cell lineage
the pattern of cell divisions
231
how many somatic cells does the adult hermaphrodite and adult males c.elegans have
hermaphrodite - 959
male - 1031
and the map of cell divisions is largely invariant
232
in c.elegans, how many larval stages are involved in egg --> adult
4
233
name the 4 gonad cells stating their function
Z2, 3 - germline stem cells - make gametes
| Z1, 4 somatic tissue of the gonad
234
describe the divisions that take place from the Z1 and Z4 cells
Z1 and Z4 divide to produce 12 somatic cells by L2. Z1ppp and Z4aaa are great granddaughters of Z1 and Z4 respectively. they form an anchor cell (AC) and a uterine cell (VU). only one of each is always formed
235
what happens at a cellular level in c.elegans upon L1 --> L2
germline cells are the same, Z1 and Z4 have undergone 3 divisions each to produce 12 cells. Z1ppp - 3 posterior divisions from Z1. Z4aaa - 3 anterior divisions from Z4. Z1ppp and Z4aaa will always sit adjacent to each other
236
what experiments were done to investigate the control in production off the AC and VU cells
Z1ppp and Z4aaa differentiation - all killing by laser ablation
1. leave all cells --> AC and VU always - never both
2. kill all but Z1pp or Z4aaa --> always gives AC
3. kill either Z1ppp or Z4aaa --> always get AC
4. kill everything but Z1ppp and Z4aa --> always AC and VU
237
what do the experiments on Z1ppp and Z4aaa differentiation tell us
Z1ppp and Z4aaa talk to each other
| Ac is default state
238
why is it likely something in the gonad that affects the differentiation of Z1ppp and Z4aaa cells
because it is surrounded by a thick basement membrane and it is unlikely a small molecule would get through
239
in a screen for mutants with defect in AC/VU cell fate what 2 genes were identified. describe the phenotype
lin12
lag2
they both have the same phenotype. LOF mutations of either cause 2xAC cells and no VU cells. since the mutants fail to make a VU cell, their normal function is to make a VU cell
240
what is the product of the lin12 gene
lin12 - the LIN12 protein is a TM receptor
241
what is the product of the lag2 gene
lag2 - the LAG2 protein is a TM ligand that binds to the lin12 receptor
242
describe the juxtacrine signalling of Z1pppa and Z4aaa in terms of lag2 and lin12 activation and differentiation
- initially lin12 and lag2 are induced and go through the secretory pathway to end up on the cell surface
- low levels of both lag2 and lin12 to start with
- randomly, more lin12 is activated sooner in one cell than the other. activated lin12 turns on more lin12 and turns off lag2 (amplification and feedback).
- the random unstable difference becomes stable and irreversible
- one cell completely activates lin12, lacking lag2, and the other cell does the opposite. active lin12 is needed to keep making lin12 (unstable). lag2 is made when lin12 is off. lin12 cannot be activated without lag2on the other cell. either cell can make either type but we are guaranteed to make both
- lin12 on --> AC
- lag2 on --> VU
243
what is the drosophila name for lin12
notch
244
what is the lin12 pest sequence
it is a single protein sequence at the carboxy terminal end that targets a protein for degradation - allows for rapid turnover
245
what is the lag2 drosophila name
DELTA
246
how is notch activated
by binding to delta through repeats (juxtacrine signalling)
247
what happens when notch is activated by binding to delta
we get ligand induced proteolytic cleavage just outside the membrane and presenilin (protease that is a component in the gamma secretase complex) mediated cleavage inside the membrane. the notch fragment interacts with protein CSL and activates target genes. Notch receptors are also TFs
248
what is presenilin needed for in the notch signalling pathway
it is needed to release the intracellular domain so it can carry out its signal transduction
249
what parts of mammalian development is notch important in
development of heart, angiogenesis, neurogenesis, intestinal cell differentiation (regulates proliferation/differentiation of intestinal SC) etc
250
mutant versions of the notch receptor can be ……...…. Activating mutations are found in many human ….. …….…...……….. …………/…………..
oncogenic
| T acute lymphoblastic leukaemia/lymphoma
251
…… signalling can repair myocardial injury
notch
252
what is the problem with blocking the gamma secretase as an Alzheimer's treatment
it reduces AB peptide but also blocks notch signalling which leads to the intestines falling apart
253
what is meant by cell adhesion being xenophobic
differentiated cells only stick to the same cell type
254
what structures are involved in cell-cell adhesion
desmosomes and adherens junctions - specific areas where sticky molecules relate to
255
what structures are involved in cell-ECM adhesion
hemidesmosomes - exist at basement of cells where they contact the ECM
256
describe adherens junctions
cadherins adhesive component
| connect to actin
257
describe desmosomes
cadherins adhesive component
| connect to intermediate filaments
258
describe hemidesmosomes
integrins adhesive component
| connect to EM collagens, lamin, fibronectin etc
259
different cells types have the same/different adhesion molecules
different - cell have signature mixes of adhesion molecules. this permits identification of and adherence to similar cells
260
what does beta catenin do
it regulates the interplay between adhesion and cell behaviour
261
what are homophilic interactions in terms of adhesion
the same cadherins stick together
262
what are the ligands for integrins of hemidesmosomes
ECM proteins
263
what are the 2 types of integrins
alpha and beta - different pairings of the 2 types provides specificity
264
the beta subunit of integrins can form cytoskeleton attachment to ………...
actin
265
how many alpha and beta type of integrins are there
7 alpha and 5 beta
266
what happens when integrins bind to the ECM
signalling molecules are recruited - different integrins cause different outcomes
267
what are ras and src
oncogenes
268
upon adhesion what does cell signalling do
it tells the cell that it has stuck to the right thing
269
explain why cell adhesion is structural and regulatory
it involves gluing (structural) and juxtacrine signalling (regulatory)
270
in what 2 ways can adhesion alter cell behaviour
via signalling pathways and cytoskeleton changes
271
what is necrosis
accidental death of cells and living tissue. generally results in swelling and bursting of the cell, release of digestive enzymes from lysosomes, and local inflammatory response
272
what is apoptosis
a regulated controlled cell death process. the cell becomes rounded, chromatin condenses and then fragments. phagocytes are attracted. membrane bound apoptotic bodies form. apoptotic bodies are phagocytosed. cellular contents are not released so no inflammation
273
what are the cellular changes seen in apoptosis
```
DNA fragmentation
membrane blebbing (reducing size of cellular but they're still membrane bound)
```
274
inter-nucleosomal DNA fragmentation is a classic sign of apoptosis/necrosis in mammals
apoptosis
275
describe the process of DNA being fragmented in apoptosis
chromosomal DNA is cut up by a non-specific nuclease. we get a ladder of small fragments. the fragmentation is a result of the chromatin structure. the linker DNA is cut by the endonuclease. the smallest fragments are the distance between one nucleosome and the next. the cell can't recover - irreversible
276
what is tunnel staining
labels free ends of broken DNA strands. the more chopped up --> the more fluorescence
277
what process removes the tissue between our fingers and toes, playing a critical role in limb morphogenesis
apoptosis - cell death in the mesenchyme of interdigital spaces accompanies the formation of free digits
278
explain why apoptosis is essential for the immune system
- negative and positive selection requires apoptosis (removal of unreactive and autoreactive lymphocytes)
- removal of excess B lymphocytes requires apoptosis
- removal of proliferated B lymphocytes after infection requires apoptosis
279
what can enhanced lymphocyte apoptosis result in
it can cause immunodeficiency
280
what can result from inhibition of apoptosis in the immune system
autoimmunity or lymphoma
281
how is apoptosis involved in neurogenesis
half of the healthy neurons born in brain development undergo apoptosis
motor neuron survival depends on synapse with muscle. more powerful input destabilises less powerful input. there is selection for the strongest synapses and these survive
282
how many cells in c.elegans are born only to undergo apoptosis
131
283
describe the c.elegans ced-1 mutant
the 131 cells are not engulfed by phagocytosis. worms with the extra cells are viable in the lab with no other obvious phenotype
284
what happens to c.elegans if we lose ced-3 or ced-4
there is no apoptosis and the 131 extra cells live
285
what happens to c.elegans when we lose ced-9
all cells apoptose
286
what is ced-4 equivalent to in mammals and what does it do
it is homologous to APAF-1 and activates downstream caspases
287
what is a caspase
a class of protease
288
what is ced-3 and what is it equivalent to in mammals
it is a caspase homologous to mammalian caspases
289
what is the relationship between ced-3 and ced-4
ced-3 is present in all cells. it is regulated by the protein encoded by ced-4. ced-3 stays inactive without ced-4 activation.
290
what is the relationship between ced-4, ced-3 and ced-9
ced-4 is negatively regulated by ced-9. if we remove ced-9 function, ced-4 activates which activates ced-3
- ced-9 --I ced-4 --> ced-3 --> apoptosis
291
where id ced-9 found and what does it do to ced-4
it site on the surface of the mitochondria in c.elegans and sequesters ced-4 and prevents it interacting with ced-3
292
what does ced-4 do to ced-3 when they interact
it physically changes ced-3s conformation. it undergoes an autoregulated internal proteolytic cleavage which activates the cysteine protease (caspase) of the protein
293
proteases are made of ………...… that are inactive. they are activated only when needed
pro-proteins
294
what is the human equivalent of ced-9
bcl2
295
what happens when bcl2 negative regulation is removed
if the negative regulation is removed by an upstream protein, part of the process results in cytochrome C being released from the mitochondria - part of the activation process of APAF1 --> caspase --> apoptosis
296
ced-9/bcl2 are proapoptotic/antiapoptotic
antiapoptotic
297
EGI-1 and other BH3 only members of the bcl2 family are pro-apoptotic/antiapoptotic
proapoptotic
| the balance between proapoptotic and antiapoptotic makes the life/death decision
298
where is oncogenic bcl2 often overexpressed and what does this cause
B cells - a translocation takes place adjacent to the immunoglobulin heavy chain enhancer. this causes follicular lymphoma (B cell lymphoma). B cells cannot apoptose
299
list factors that can induce apoptosis
DNA damage, oncogene activation, unfolded proteins, loss of growth factor stimulation, gain of TGF beta signalling (predominantly anti-proliferative role)
300
what is p53 and what does it do
tumour suppressor - it protects against cancer and can induce apoptosis. it integrates multiple stress/damage sensing systems in the cell and can activate the death pathway
301
what is the p53 response to moderate damage
induce DNA repair and the cell returns to normal
302
what is the p53 response to severe genome damage
senescence
303
what is the p53 response to sever genome damage and hyperproliferation
apoptosis
304
what are some functions of TGF beta signalling
it has tumour suppressor functions, is involved in cell division, dorsal ventral specification, growth control (inhibition of cell division), cellular homeostasis (promoting apoptosis in some breast cell tissues). how a cell responds to TGF beta signalling depends on its context
305
how is TGF beta involved in cancer
many tumours have either inactivating mutations in TGF beta receptors or smad proteins. most pancreatic cancers have a deletion in the gene encoding smad 4. many cancers are unresponsive to TGF beat growth inhibition. mutations block TGF beta signalling, causing resistance to growth inhibition and failure to undergo TGF beta mediated apoptosis
306
smad genes act up/down stream of TGF beta
downstream
307
TGF beta is a critical extrinsic/intrinsic regulator of apoptosis in the developing limb
extrinsic
308
what are the 3 hallmarks in apoptosis
decision to die --> dying process --> dead cell
309
what are the 3 principle axes of the body
anterior/posterior - defines mouth and anus
dorsal/ventral - defines back and front
left/right - defined automatically once A/P and D/V are established
310
what is gastrulation
a movement and reorganisation of cells from the blastula that is linked to creation of 3 layers of SC - ectoderm, mesoderm, endoderm
311
all ..…...…. are tripoblastic
bilateria
312
what is meant by tripoblastic
have a mouth, gut and anus (A/P), a back and front (D/V) and a left and right
313
when are the 3 body axes in c.elegans established and what defines them
from the first 2 cell division we create 4 cells where the A/P and D/V and L/R axes are already established
D/V - vulva on ventral side
L/R - 20 epidermal cells at either side
314
in c.elegans there is symmetry and ……….. symmetry
broken
315
the hermaphrodite c.elegans has 2 arms to the gonad whereas the male only has one - what process allows for this
apoptosis kills off the other part of the gonad in males
316
describe the c.elegans body muscle symmetry
4 segments each with 2 internal segments
317
describe the broken symmetry in c.elegans
intestine displaced to one side and the gonads to the other
318
in c.elegans the unfertilised egg has polarity/non polarity
no polarity
319
what defines the posterior end of c.elegans
sperm entry
320
describe the 2 cell stage of c.elegans
there is an AB cell at the anterior end and a P1 cell at the posterior end
321
describe the 4 cell stage of c.elegans
```
ABp cell at the dorsal side
EMS cell at the ventral side
ABa at the anterior side
P2 at the posterior side
P1 --> P2 + EMS
AB --> ABa + ABp
```
322
describe the 1st cell division in c.elegans
it is asymmetric
| AB is larger and molecularly distinct from P1
323
the point of sperm entry determines the posterior end OR the point of sperm entry is defined by the posterior end
the point of sperm entry determines the posterior end
324
describe the PIE-1 mutant and its WT function
PIE-1 is a maternally supplied c.elegans protein present in the oocyte. in the mutant the P2 cell is transformed into a second EMS cell. the mutant has 2xEMS cells and no posterior end. EMS makes 20 epidermal cells but we get 40 in the mutant. PIE-1 WT role is to define the difference between a posterior cell (P2) and EMS (ventral cell)
325
what happens when sperm enter the egg in c.elegans
pseudodivision - cleavage furrow makes it look like division is about to occur. the sperm and egg nuclei then fuse then the 1st cell division occurs. PIE-1 concentrates in the posterior end
326
…… ……………… segregate to P1 then P2
P granules
327
how do PIE-1 become distributed after fertilization
it is segregated to P1 then P2 and rapidly degraded in EMS
328
what makes P2 different from EMS
in PIE-1 mutants blastomere P2 develops as EMS. therefore PIE-1 makes P2 different from EMS
329
at the stage in development where P2 and EMS become different, are ABa and ABp different
no - they are still the same at this stage
330
WT EMS has/doesn't have PIE-1
doesn't have
331
describe par mutants and what is the WT function
they are defective in A/P polarity. PIE-1 is not differentially segregated. par proteins correctly localise PIE-1
par protein --> PIE-1 --> posterior determination
332
what divides first AB or P1
AB
333
describe what happens when AB divides
the bottom cell moves more anterior and ventral and the other cell moves more posterior and dorsal
334
what happens when P1 divides
its more ventral cell moves under ABa and ABp (EMS) an the other cell (P2) sits at the back
335
describe the poking a cell and moving it backwards experiment
P1 is forced to divide in a different direction
ABa is now more dorsal and ABp more anterior
ABa is in contact with P2, not ABp
the EMS position still determines the ventral side. EMS is displaced vertically by pushing ABa and ABp round
ABa and ABp positions have switched places
336
how do we know that ABa and ABp have the same developmental potential
they can carry out the other cells role when their positions are switched. the difference must result from their spatial position
337
ABa and ABp both make the …………. receptor
GLP-1
338
P2 becomes different to EMS when ………. localises
PIE-1
339
because of PIE-1, P2 turns on ………. and ……….
APX-1 and MOM-2
340
what is MOM-2
a signal for the wnt pathway
341
EMS makes the ………… receptor (wnt pathway receptor)
MOM-5
342
wnt signalling regulates the behaviour of …...… in its subsequent divisions
EMS
343
what is the ligand for GLP-1
APX-1 (notch pathway)
344
what does APX-1 do
it tells the more posterior cell (ABp) to become ABp and not ABa
345
P2 acts as a ……...… ……...….. …......….
posterior signalling centre
346
what makes the EMS daughters (E ams MS) different
MOM-2
347
what is induction
communication between cell that induces changes
348
why are xenopus laevis good model organisms for studying development
they have big eggs which are easy to study
349
the xenopus egg is polar/apolar
polar - cytoplasm is different colour at different ends due to protein localisation
350
which body axis does the xenopus animal/vegetal axis correspond to
the anterior/posterior axis
351
what is the role of the TF, VegT
it accumulates in and determines the vegetal (posterior) end
352
how is sperm entry different in xenopus from c.elegans
sperm enter at the animal pole and the polarity is defined before sperm entry - the sperm will only enter at a certain place
353
describe the xenopus 4 cell stage
it is divided into dorsal/ventral halves which are defined by sperm entry and the nieuwkoop centre
354
the ventral half of the xenopus 4 cell stage lacks a …….…….… …......……. and develops into a ……...… …......…
nieuwkoop centre
| ventralised embryo
355
the dorsal half of the xenopus 4 cell stage develops into a …………. embryo
dorsalised
356
sperm entry in the xenopus causes …………… of protein
relocalisation
357
the NC is at the same/opposite side of sperm entry in xenopus
opposite
358
describe the 1st cell cleavage in the xenopus
it usually bisects sperms entry and the NC to give the left/right axis
359
describe the 2nd cleavage in xenopus
it cleaves the cells into dorsal/ventral halves
360
how can we graft cells and give a transplant example
suck single cell with glass pipette. transplant cell
e.g. transplant NC to ventral --> twinned dorsals --> dorsalised embryo. graft cell instructs adjacent cells to become dorsal
361
do graft cells contribute to mesoderm and ectoderm
no they remain endoderm
362
does grafting ventral --> dorsal have an effect
no
363
describe the NC
endoderm with dorsalising abilities
364
what pathway allows communication between graft and host cells
an unusual form of the wnt pathway
365
describe what happens upon fertilisation in the xenopus
there is complete movement of cytoplasm when sperm enters. vesicles are moved to an area opposite the point of sperm entry by the cytoskeleton. these define the NC.
366
the wnt pathway:
microtubules that mediate ………...…. ……….. also transport membrane vesicles from the vegetal pole. these vesicles transport dishevelled protein (part of the wnt pathway) injected into the cell. in the wnt pathway there is a receptor (……...) normally on the outside of the cell that binds dishevelled (activated receptor activates pathway) and stabilises ……… ………...… . elevated beta catenin plus vegetal side creates the NC
cortical rotation
frizzled
beta catenin
367
in xenopus, how is the wnt pathway activated
from a source internal to the cell - from internal vesicles
368
how do we know beta catenin is involved in dorsal axis specification
injection of beta catenin into vegetal cells induces a second dorsal side
369
describe the 4 steps involved in the specification of axes
1. vegT accumulates and defines vegetal (posterior) end
2. beta catenin accumulates in and defines dorsal side (initiated by sperm entry which results in localisation of wnt signalling vesicles)
3. concentration differences mark a molecular map of axis formation
4. outcome - differential expression of nodal related proteins in endoderm
370
what are nodal proteins
members of the TGF beta superfamily
371
highlight the differences and similarities in development between c.elegans and xenopus
1. in both, differential localisation of factors in the zygote help establish the A/P axis
2. signalling establishes D/V axis. Notch and wnt in c.elegans and wnt then subsequently nodal in xenopus
3 xenopus - wnt-dorsal, lack of wnt-ventral
c.elegans - notch-dorsal, wnt-venral
372
nodal related proteins are …...………..
organisers
