Biol 303- Module 3 Flashcards
Differentiation
Process by which unspecialized cells become specialized
Commitment
State in which cell development becomes restricted.
Specification- 3p
- First stage
- capable of differentiating in neutral env
- reversible
Determination- 3p
- Second stage
- irreversible
- differentiate in a non-neutral env
Autonomous Specification - 4p
- Mosaic Dev
- Predominant in most invertebrates
- Differential Acquisition of Morphogenetic Determinants.
- Invariant
Invariant - 2p
- Blastomeres are Invariant
- cells k now their fate without interacting with other cells
Mosaic Dev-
If blastomere is lost embryo doesn’t compensate ny having other cells change fate.
Conditional Specification - 7p
- Regulative dev
- Predominants in vertebrates
- Cell- Cell interaction (Juxtacrine)
- Relative position is key
- Paracrine secreted signals
- Variable cleavage division
- Fate assignment- flexible
Regulative Dev
If blastomere is lost the embryo can compensate.
Transplant
cells can adapt to new env
ablate
surrounding cells adapt/recover structure
Reality of Roux vs Drisech
Embryos can use combination of both autonomous and conditional specification
Driesch vs Roux - 4p each
Roux
1.Mosaic autonomous Dev
2. Hot needle on one side of the blastula
3.The side became dead tissue
4. Half embryo left with one living sides.
Drisech
1. Conditional Regul Dev
2. Removed fertilization envelope
3. Separated 4 cells.
4. Plutei developed from single cells.
Morphogen -
Definition, function, location, diffusion, whats forms, highest conc?
- Form Giver
- Substance that specify cell fates differentially with by their differing concentration.
- Made on specific sites in an embryo.
- Diffuse over long distance
- Form concentration gradient
- Highest conc- point of synthesis.
Syncytium - why does nuclei reside in cytoplasam?
- Many nuclei reside in a common cytoplasm
- Results from karyokinesis (Nuclear division)- without cytokinesis or from cell fusion.
Syncytical Specification -
Interaction,Location
- Interaction of nuclei and Transcriptional factor
- takes place in a common cytoplasm.
Syncytial Blastoder- why like drosophila embryo
- Drosophila Embryo
- No cell membrane exist other than that of the egg itself.
Stages of Syncytial Blastoderm
Stage 1- Newly laid egg
Stage 2- Early Cleavage
Stage 3- Pole cell formation
Stage 4- Syncytial Blastoderm
Stage 5- Cellularization.
Syncytial Specification-Which class uses most?
How body regions specified
Fate?
Specifications after cellularizaton?
- Most insect classes
- Body regions are specified by interactions between cytoplasmic regions prior to cellularization.
- variable cleavage- no rigid cell fates for any particular nuclei- random nuclear distribution
- After cellularization- both auto and conditional specification used.
Bicoid and Caudal are what? importance?
Morphogens, laid down in opposing gradients.
How does syncytial specification work?
- Bicoid and Caudal laid down in opposing gradients
- Syncytial nuclei become distributed evenly through out the cytoplasam
- Location before cellularization determines how much morphogen in each cell.
- combinatorial effect -> specification anterior and posterior body plan.
Fertilization triggers the beginning of embryonic development known as?
Activation
Spermtogenesis
sperm are highly specialized cells.
Haploid nucleus
What replaces histones and why?
Streamlined, DNA tightly compacted,
Protamines, small arginine replace histones- denser packaging of DNA in sperm head.
Where is acrosome?
Derived from?
What does it contain?
Infront of nucleus
Derived from Golgi
contains enzymes and complex sugars.
Sometimes what is between acrosome and nucleus?
Area enriched in globular actin.
Word for no tail?
Aflagellate
Dynein- Protein? Atpase?
Function?
Result?
Protein- Attached to the axoneme- provides force for sperm propulsion.
Atpase- converts the released chemical energy into mechanical energy allow active sliding of the outer droplet.
Results Flagellum to bend
oocyte
-developing egg cannot yet bind to sperm or fertillize.
What do eggs consist of? 6p
Nutritive proteins
ribosomes and tRNA
mRNA’s
morphogenic factos (transcription & paracrine)
protective factors (UV filters, DNA repair enzymes etc)
First Meiotic prophase- 5 substages
- leptotene-
- zygotene-
- Pachytene-
- diplotene-
- Diakinesis
leptotene
leptotene- condensed chromatin becomes apparent.
zygotene-
zygotene- homologous chromosomes pair up, synaptonemal complexes form between the homologous chromosomes.
Pachytene-
Pachytene- thickening of chromosomes and genetic recombination- aka crossing over.
diplotene
diplotene-sister chromatids of homologous chromosomes seperate from each other as synaptonomal complex breaks down
Diakinesis
a further condensation of the chromosomes and, simultaneously, a further seperation of chromatids- hang together at the chiasmata.
egg cell membrane
fusion with sperm cell membrane, regulation
extracellular matrix
fibrous mat around the egg – often involved in sperm-egg recognition.
vitelline envelope (or membrane)
invertebrates: extracellular matrix is a thin tough layer
of glycoprotein meshwork (egg jelly
surrounding the vitelline envelope (either attracts or activates sperm)
the zona pellucida
mammalian eggs: extracellular envelope is a thick matrix
cumulus
layer surrounds zona pellucida
a layer ovarian follicle cells that were nurturing the egg at time of its release from the ovary
corona radiata
The innermost cumulus cells
General Interaction of egg and sperm- 5p
sperm is attracted to egg by chemoattraction – soluble molecules secreted by egg (highly species specific)
exocytosis of sperm acrosome (releasing its enzymes)
sperms binds to extracellular matrix (vitelline envelope or zona pellucida)
sperm makes its way through extracellular matrix
egg and sperm membranes fuse
why use sea urchins as experimental model
they are sexually mature throughout year
they can produce considerable numbers of large, transparent eggs
Oscar Hertwig (1876) observations
only one sperm entered each egg and that resulting embryo resulted from mitotic divisions of the nucleus created at fertilization.
How can sea urchins gametes be shed?
Sea urchin gametes can be shed from adults by injecting 0.5 M KCl (potassium choride) into the intracoelomic cavity.
Chemotaxis:
Directed movement of a cell in response to a chemical gradient, such as sperm following a chemical (chemoattractant) secreted by the egg.
Chemoattractant peptides also activate sperm and are called
sperm-activating peptides (SAPs)
The acrosomal reaction
- acrosome membrane & sperm cell membranes fuse (results in exocytosis of acrosomal content)
- extension of acrosomal process (actin polymerization).
Triggered by contact with egg jelly (sea urchins).
Released acrosomal enzymes digest a path through the jelly layer.
Once through, the acrosomal process adheres to the vitelline envelope – also may digest vitelline envelope where attached
What triggers the acrosome reaction in sea urchin sperm?
receptors on the sperm plasma membrane contact species-specific sulfated polysaccharides on the egg jelly coat – this initiates the acrosome reaction
Binding to what specific receptor of the sperm membrane results in acrosomal reaction
Binding of sulfated polysaccharides to receptors initiates the acrosomal reaction by activating other sperm membrane proteins.
3 egg sperm interactions once through the jelly coat
(1) Small peptides released from egg jelly result in chemoattraction and sperm activation.
(2) Sulfated polysaccharides of the jelly coat bind receptors on sperm to promote the acrosome reaction.
(3) A 3rd level of species specific interaction occurs when sperm acrosomal process contacts the vitelline envelope (sea urchin). An acrosomal protein called bindin binds to dejellied eggs (exposed vitelline envelope) in species specific manner.
three events for union of sperm and egg?
The sperm must 1) find the egg, 2) undergo acrosome reaction to penetrate jelly coat, then 3) adhere to vitelline envelope.
Functions of Bindin
2p
Required protein for fusion of sperm
attachment of sperm to the vitelline envelope.
One property of bindin
has a long stretch of hydrophobic AAs near NH2 terminus – this “fusogenic region” can promote membrane fusion
polyspermy
more than one sperm entering egg)
(triploidy
if two sperm enter > three sets of chromosomes
sperm derived centrioles
two spindles segregating three chromosome sets is a disaster
how does the egg prevent polyspermy?
strategy is to prevent entry of second
fast block (electric change in egg membrane)
slow block (exocytosis of cortical granules).
how does fast block for polyspermy work?
ions pumps maintain a resting membrane potential of -70mV (inside is negatively charged wrt exterior) > in sea urchin lots of Na+ ions outside egg and little inside
How does influx of NA prevent polyspermy.
influx of Na+ 1-3 s after binding of first sperm membrane & potential shifts to +20mV which prevents further sperm–egg membrane fusion – possibly “fusogenic” region of bindin cannot work on a positively charged surface
How does slow block work in oreventing polyspermy?
cortical granule reaction – a slower and mechanical block to polyspermy found in many animals – sea urchins and most mammals.
sperm entry triggers cortical granules to fuse with egg membrane – releasing the cortical granule contents – several proteins including cortical granule serine protease
cortical granule serine proteins cleaves protein “posts” that connect the vitelline envelope to the egg membrane
mucopolysaccharides are also released from cortical granules – bind to vitelline envelope, absorb water and push the vitelline envelope away from the egg membrane = fertilization envelope
How are fertilization envelopes stabilized?
by enzymatic cross-linking of proteins
what does Protein cross-linking enzymes include
include the egg specific peroxidase (ovoperoxidase = OVOP) and transglutaminase (TG) from the cortical granules.
cortical granules contain:?
*cortical granule serine protease (CGSP)
*mucopolysaccharides
*protein cross-linking enzymes (TG and OVOP)
*hyalin (a glycoprotein)
What does hyalin do?
hyalin forms a coat around the egg – egg extends long microvilli into hyaline layer – structural support
WHat is hyalin
a large fibrillar glycoprotein (~330 kDa) that multimerizes in the presence of calcium.
How does the cortical granule reaction occur?
at fertilization free Ca2+ conc. in egg cytoplasm increases
triggers egg/cortical granule membrane fusion
calcium release passes across the egg in a wave starting at point of sperm entry(dyes exist that fluoresce when bound to Ca2
where does the calcium come from?
stored in the endoplasmic reticulum (in sea urchins and mammals)
what is aequorin
a protein that becomes luminescent upon binding Ca++
How are calcium channels opened?
Channels are opened by inositol 1,4,5-triphosphate = IP3 (throughout animal kingdom).
Sea Urchin eggs- how does PIP2 Mediate
Activation of the bindin receptors activates PLC
PLC cleaves PIP2 in the egg plasma membrane releasing IP3
IP3 is released into the egg cell cytoplasm.
IP3 diffuses to the ER, where it opens Ca2+ channels.
How is phospholipase C activated?
soluble factors released from sperm at membrane fusion
or
through signal transduction by activation of receptor tyrosine kinase on egg membrane
In sea urchins:
female meiosis is completed
prior to fertilization
In sea urchins sperm chromosomes must undergo decondensation- what is that?
removal of sperm-specific histones and addition of maternal histones
In sea urchins:
the male and female pronuclei migrate where and do what?
migrate towards each other and fuse
In sea urchins:
DNA replication generally takes place when?
after fusion of pronuclei
In sea urchins:
sperm centriole is used to do what?
assemble mitotic spindle (this is usually the case – exception is in the mouse)
In sea urchins what disintegrate in the egg?
sperm mitochondria and flagellum
Process of Sperm in Sea urchins- 5 steps
- Sperm contacts Jelly layers
- Acrosome Reaction
- Digestion of jelly layers
- Binding to vitelline enveloppe
- Fusion of acrosomal process membrane and egg membrane
Where does Mammalian fertilization begins? and how?
- begins in the oviduct with binding of free-swimming sperm to the ovulated egg extracellular coat, the zona pellucida (ZP)
form a single “activated” cell, the zygote
the sperm acrosome reaction (a form of cellular exocytosis)
penetration of the egg ZP by sperm
fusion of egg and sperm membranes
the egg cortical reaction
zona reaction (results in alteration of the ZP such that free-swimming sperm are unable to bind to fertilized eggs)
Three stages of human oogenesis
(1) the meiotic prophase events
(2) follicle formation
(3) oocyte growth
(1) the meiotic prophase events occurs what and where?
synapsis and recombination, which occur in the fetal ovary
follicle formation
, which occurs during the second trimester of fetal development and is associated with a dramatic loss of oocytes caused by atresia (cell death and absorption)
oocyte growth
which occurs in the adult ovary and culminates in the resumption and completion of meiosis I and ovulation of a metaphase II–arrested egg.
Undifferentiated ovarian germ cells that give rise to the oocytes are known as
oogonia
Oogonia that have initiated meiosis are known
as primary oocytes.
Completion of the 1st meiotic division produces a small cell called and large?
polar body and secondary oocyte
