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Biology of development > Anterior-Posterior patterning > Flashcards

Anterior-Posterior patterning Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

what is the general way that cells acquire positional information?

A

morphogen gradients

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2
Q

what is the definition of a morphogen?

A

a biological molecule. the concentration of which varies according to position thereby conveying positional information

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3
Q

what is the sequence of events that lead to the formation of an oocyte in a female drosophila?

A

initially one stem cell is produced and travels down the reproductive tract. As this happens the stem cell divides asymmetrically 8 times. but only one becomes the oocyte and the others become nurse cells. cytoplasmic bridges between the cells transfer the content of the nurse cell into the oocyte and eventually the nurse cells die, allowing the oocyte to expand. following fertilisation the oocyte becomes multinucleic and the nuclei moves to the border of the oocyte and then membranes form between the nuclei and you achieve a syncitial (?) blastoderm

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4
Q

what are the maternal/egg polarity group?

A

a group of genes that exists before fertilisation at opposite ends of the oocyte- the posterior and anterior end. they exiss in a gradient across the embryo

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5
Q

how were maternal/egg polarity group first discovered?

A

scientists noticed that larvae who’s mothers were mutants for certain genes developed defects despite their genome being intact- this suggested that the mother was the source of the patterning signals

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6
Q

what are the three subgroups of matenal/ egg polarity genes?

A

anterior, posterior or terminal

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7
Q

what do mutants for the posterior egg polarity genes look like?

A

the have a tail region and an abdomen but no head regions

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8
Q

what experiments proved that bicoid was a morphogen?

A

injecting bicoid into a bicoid deficient offspring rescues the phenotype, injecting bicoid into a normal embryo in the centre forms a two headed mutant, injecting bicoid into the centre of the biked mutant causes a head to form in the middle. adding bicoid to the posterior end of the wild type forms a two headed mutant. increasing the level of bicoid by using droso with a duplicated genome who expressed more copies of bicoid also moved the cephalic furrow back- shows the gradient effect of bicoid

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9
Q

what is the name of the two anterior maternal/ egg polarity genes?

A

hunchback and bicoid

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10
Q

what are the names of the two posterior maternal/ egg polarity genes?

A

caudal and nanos

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11
Q

how is the bicoid protein transported out of the nurse cells? once in the oocyte how is it transported to the anterior pole

A

via microtubules using a kinesin ATPase. it then associated with dyneins which take it to the anterior pole

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12
Q

how does bicoid interact with posterior maternal genes?

A

inhibits caudal mRNA from the anterior

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13
Q

how do the anterior and posterior maternal egg polarity genes come to be at the different poles?

A

the mRNA of each is transported into the oocyte via the nurse cells and is transported to the opposite poles

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14
Q

how is nanos mRNA localised in the posterior pole?

A

the nanos mRNA is transported into the oocyte. it is bound to oskar protein which is transported via kinesin to the posterior pole of the embryo. it then anchors nanos to the membrane, allowing it to be translated

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15
Q

what protein facilitates the localisation of the oskar protein?

A

staufen

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16
Q

what traps the nanos in the posterior end of the oocyte?

A

oskar portein

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17
Q

if the mRNA of the maternal egg polarity genes are bound to the poles, how can the diffusion of their messages occur?

A

the protein products of the mRNA is not bound so this is free to form a diffusion gradient

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18
Q

how are hunchback and caudal localised in the cell and how do they become localised to a specific pole?

A

their mRNA is distributed evenly throughout the cell but nanos represses the translation of hunchback and bicoid inhibits the translation of caudal- so they can only be translated in certain poles

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19
Q

what is the affinity of the head gene promoters to bicoid and why?

A

has a low affinity so they are only activated in very high concentrations

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20
Q

what determines the expression of head genes?

A

bicoid and hunchback act together

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21
Q

what are the 4 types of genes involved in segmentation and the initial patterning of the anterior to posterior axis

A

maternal/ egg polarity genes, gap genes, pair rule genes, segment polarity genes.

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22
Q

what is the role of exuperantia and swallow? what occurs in their absence?

A

they keep the bicoid mRNA at the anterior pole, in their absence the bicoid diffusion gradient is larger

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23
Q

how do bicoid and hunchback interact?

A

bicoid acts as a transcription factor of hunchback

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24
Q

what is the general role of segmentation genes?

A

the transition from specification to determination in dros is mediated by segmentation gene that divide the early embryo into a repeating series of segmental primordia along the AP axis.

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25
Q

what are the 5 gap genes?

A

hunchback, kruppel, knirps, giant, tailless

26
Q

what is the suppressing relationship between the the gap genes? what occurs as a result of some of the interactions?

A

hunchback surpresses giant, which surpasses kniprs which surprises Kruppel.
- giant and cripples mutually repress
knirps and hunchback mutually repress hunchback
- however there are some overlapping regions e.g.. Knirps overlaps with kruppel

27
Q

how do bicoid and hunchback, nanos and caudal activate the gap genes?

A

the gap genes are activated by different gradients of each of the maternal proteins.

28
Q

what is the first indicator of segmentation in the fly embryo?

A

the expression of the pair rules genes

29
Q

how do the pair rules genes divide the embryo up?

A

the form the precursors of the segmental body plan.

30
Q

how are pair rule genes expressed across the larvae and what is the reason/ result of this?

A

there are 8 genes known to act as pair rule genes. each forms 7 stripes across the embryo

31
Q

how are pair rule genes expressed across the larvae and what is the reason/ result of this?

A

there are 8 genes known to act as pair rule genes. each forms 7 stripes across the embryo. however their stripes overlap so that each cell in the parasegment (there are 4 cells per parasegment)

32
Q

what is the layout of the enhancers for each pair rule gene? why is this?

A

the enhancers for each gene is thought to be modular so that expression of each stripe in controlled by a modulator of the enhancer. it is thought that because of this, different concentrations of gap genes determine the expression of each gene in a stripe

33
Q

what is an example of the special layout of a pair rule’s enhancer?

A

the modular layout of the pair rule gene’s enhancer can be seen in the even skipped gene. each unit regulates expression of the gene in a certain stripe due to the gap gene concentrations that are present at each stripe. the stripe 2 expression of even skipped is activated by bicoid and hunchback but repressed by giant and kruppel. therefore, the only time this can happen is where the area os stripe 2 is.. the enhancer region for this stripe contains binding sites for all 4, supporting the argument.

34
Q

how can the regulation of the pair rule expression be demonstrated in an experiment?

A

identify a sequence that looks like it might have transcriptor binding activity, clone or cut it out and make a trsnagene which consists of a promoter or a reproter gene such as lacZ gene. inject into fly embryo and see where it is. overlap with eve expression and see it is the same area. cut down til minimum about of sequence needed and this is cis regulatory element.

35
Q

how can the regulation of the pair rule expression be demonstrated in an experiment?

A

identify a sequence that looks like it might have transcriptor binding activity, clone or cut it out and make a transgene which consists of a promoter of a labelling gene such as lacZ gene. inject into fly embryo and see where it is expressed. overlap with eve expression and see it is the same area. cut down til minimum about of sequence needed and this is cis regulatory element.

36
Q

what is an example of the special layout of a pair rule’s enhancer?

A

the modular layout of the pair rule gene’s (cis regulatory elements) enhancer can be seen in the even skipped gene. each unit regulates expression of the gene in a certain stripe due to the gap gene concentrations that are present at each stripe. the stripe 2 expression of even skipped is activated by bicoid and hunchback but repressed by giant and kruppel. therefore, the only time this can happen is where the area os stripe 2 is.. the enhancer region for this stripe contains binding sites for all 4, supporting the argument.

37
Q

how are pair rule genes expressed across the larvae and what is the reason/ result of this?

A

there are 8 genes known to act as pair rule genes. each forms 8 stripes across the embryo. however their stripes overlap so that each cell in the parasegment (there are 4 cells per parasegment) - each has its own identity due to a combination of pair rule genes than any other in the segment

38
Q

how is ftz expressed? (what type of gene is it)

A

ftz is a secondary pair rule gene whose mRNA and its protein are seen throughout the segmented portion of the embryo however as the primary par-rule genes begin to interact with the fez anticancer, the fez gene is repressed in certain bands of nuclei to create an interstripe region. fez also induces its own expression

39
Q

what is the role of the segment polarity genes?

A

i far our discussion has described interactions between lolecules within the syncytial embryo. But once cells form, nteractions take place between the cells. These interactions
are mediated by the segment polarity genes, and they accomplish two important tasks.

40
Q

what occurs when wingless or hedgehog are mutated in the segments?

A

Mutations in these genes lead to defects in segmentation and in gene expres-
Dn pattern across each parasegment.

41
Q

what is the general pattern of expression of the segment polarity genes in a parasegment?

A

one row of cells must express hedgehog and one row must express wingless

42
Q

how is the expression of wg and hh in a parasegemnt initially triggered?

A

the engrailed gene expression which is activated in cells that have high levels of even skipped or ftz

43
Q

what does the expression of engrailed mark in each parasegment?

A

the anterior portion

44
Q

in what region of the parasegment is wg expressed? and where does this only occur?

A

in areas of the parasegment which have no evenskipped or ftz, this only occurs in the cell anterior to the engrailed cell

45
Q

how is the expression of wg and engrailed in adjacent cells maintained after pair rule genes stop being expressed?

A

in the cell transcribing the wingless gene, wingless mRNA is transported to the apex of the cell where it is translated and released. the cells expressing engrailed can bind this protein as they have frizzled receptor, this activates dishevilled which inhibits the activity if zw3 which normally activate armadillo (b-cat) which tags b cat for degradation when the wnt pathway isn’t activated. so when wnt activates the engrailed cell, armidillo can enter the nucleus and activate transcription of engrailed and hedgehog. engrailed then binds to patched and allows smoothened protein to activate cubits interruptus which activates wg transcription

46
Q

what does hh bind to on the wingless expressing cell? what does this activate?

A

patched, prevents patched from inhibiting smoothed protein. this then activates cubits interrupts which activates wingless

47
Q

what is the consequence of the interactions between the wingless expressing cells and the engrailed expression cells. how can this different identity be seen the in the segments?

A

a gradient of wingless and hedgehog forms across the parasegment. the gradients formed by this is thought to determine the identity of the cells in the parasegment.
- on the dorsal segments: 1° row of cells consists of large, pigmented spikes called denticles. Posterior to these cells, the 2° row produces a smooth epidermal cuticle. The next two cell rows have a 3° fate, making small, thick hairs; they are fol- lowed by several rows of cells that adopt the 4° fate, pro- ducing fine hairs

48
Q

what is the patterning of hairs on a dorsal segment?

A

1° row of cells consists of large, pigmented spikes called denticles. Posterior to these cells, the 2° row produces a smooth epidermal cuticle. The next two cell rows have a 3° fate, making small, thick hairs; they are fol- lowed by several rows of cells that adopt the 4° fate, pro- ducing fine hairs

49
Q

overall, what is the outcome of the expression of the segment polarity genes?

A

he resulting pattern of cell fates also changes the focus of patterning from parasegment to segment. There are now external markers, as the

50
Q

what suppresses engrailed?

A

odd-skipped and runt

51
Q

what activates engrailed?

A

even skipped and ftz

52
Q

where can the expression of wingless only occur?

A

in the cells anterior to the cell expressing engrailed

53
Q

what level of gene expression enable wingless to be expressed?

A

in areas containing no even skipped or ftz but no express sloppy

54
Q

where is the cell expressing wingless found in the parasegment?

A

the most posterior part

55
Q

what are the 4 regions of parasegments and how can these be used to show that hedgehog and wingless act as morphogens?

A

the first is randomly directed denticles, the second is smooth, the third is smooth cuticles, the fourth is directed denticles. when Use of a heat shock inducible hh transgene shows that high levels of Hh protein specify fate 1, lower levels fate 2 and very low levels fate 3

56
Q

how was hh shown to acts as a morphogen?

A

high levels of Hh protein specify fate 1, lower levels fate 2
and very low levels fate 3

57
Q

how is the expression of wingless and hedgehog prevented from spilling into surrounding parasegments?

A

Wg and hh signalling restrict the movement of, respectively, Hh and Wg protein.

58
Q

what are the two theories for how the hh and wingless signals acts as morphogens?

A

Either each signal acts in a graded manner to specify the fates of cells at a distance from these sources, or each signal acts locally on the neighboring cells to initiate a cascade of inductions

59
Q

what supports the theory that hedgehog is transmitted from cell to cell?

A

a study looking at sonic hedgehog signalling in limb bud formation found that actin based filapodia extended from the signalling cell and contain Shh, it is postulated that these extensions make contact with filopodia from the responding cell when Shh is released and interacts with the receptor. this mechanism could be used for hh signalling in the dros segment patterning

60
Q

what has been shown to occur when you knock out different gap genes?

A

they leak into each others areas showing that they repress each other

Biology of development (6 decks)

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