Leacture three limb bud formation Flashcards Preview

Advanced developmental biology > Leacture three limb bud formation > Flashcards

Flashcards in Leacture three limb bud formation Deck (29)
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1
Q

what are the three parts of a limb (p to D)

A

stylopod, zeygopod, autopod

2
Q

when does limb foration start in the chick

A

3 days

3
Q

when does kimb formation start in the mouse and when is it formed

A

10 daysto 14 days

4
Q

where doe the limb bud form

A

junctin between the dorsal and ventral ecotderm

in distinct position along the AP axis

5
Q

what experiment shows the AP axis is established very early

A

take presomiic mesoderm and graft back in incerted = somites form in reverse order
this shows cells have been predetermined with their positional identity

6
Q

how is fgf8 expressed

A

gradientwith highest at the posterior

7
Q

what is the expression attern of retinoic acid

A

is highest in the mid trunk of the embryo and declines both posteriorally and anteriorally

8
Q

what is the role of the fgf8 and RA gradients

A

give positional identity to cells along the AP axis

an address of where they are on it

9
Q

what other signally are also important in establishing the AP axis

A

WNts and BMPS expressed in posterior (WNT and BMPantagonists expressed in anterior)

10
Q

what is th eoutcome of the signalling gradients

A

RA/WNT3a and fgf8 activate TF (cdcxs) these then activate Hox genes
hox genes inv in AP patterning

11
Q

what are properties of HOx genes

A

homeotic TFs
evolutionary conserved
show colinearity
in their order along the chromosome and spatial/temporal pattern along the AP axis

12
Q

where are 3’ hox genes expressed

A

at the anterior

13
Q

what do the expression pattern of Hoxb genes show

A

shows anterior borders are distinct whilst posterior are not

14
Q

how does hox expression explain the difference in the number of cervical vertebrae on the mouse

A

the chick has twice as many as mouse

has a bigger hox 5 expression (=hox5/6 boundary is change in the type of rib)

15
Q

what does hox expression in the snake show

A

doesnt allow for limbs
as norm region anterior to hoxc6 becomes forelimb
in snake hoxc6 expressed thoroughout - no anterior region of its expression = no limb
expansion of hoxc6 and hoc8 expression correlates with the expasion of thoracic identitiy of skeleton as no act of necessary signalling pathways

16
Q

what is the role of fgf10 and how was this shown

A

in lpm
initiates limb bud formation
is expressed in the correct areas jus tprior to fomation
ectopic expression induces and ectopic limb
ko = no limb = is necessary

17
Q

what is the TF that activates fgf10

A

Tbx5

18
Q

what controls the position of fgf10

A

tbx5 activation
tbx5 expression is activated by the rostral hox code (hox4/5)
and tbx5 expression is repressed by caudal hox code expression

19
Q

where does the fgf10/hox/tbx signalling occur

A

in the lateral plate mesoderm

20
Q

what does fgf10 induce in the ectoderm of the limb bud

A

fgf8 expression

21
Q

what TF is expressed in the forelimb bud

A

tbx5

22
Q

what TF are expressed in the hindlimb bud

A

Tbx4 and Pitx1

23
Q

what does inducing an ectopic limb etween the two normal limb buds with a fgf10 bead show

A

in the ectopic limb there is chimeric expression of the tbx gnees = this is consistent with these genes being progeitors for the HL and FL

24
Q

in the chick what is the consequence of tbx4 overexpression and what is the consequence of tbx5 overexpression

A

tbx4 takes on HL identity (wt= FL)

tbx5 takes on FL identity (wt= HL)

25
Q

what do the overexpression expreiments of tbx genes in the chick show

A

confirms their role in the FL/HL identitiy

26
Q

what occurs in the mouse if KO the tbx genes

A

tbx4 - defect in hl

tbx5 - defect in fl

27
Q

what do conditional ko and rescue of tbx4 show

A

(KO tbx5 then put in tbx4) shows that tbx4 is not sufficient to give hindlimb identity in the mouse = ptype still resemble FL

28
Q

what do experiments with pitx1 show

A

misexpress in fl gives more hl id
ko = loss of hl feature
when do condtional ko of tbx5 then save with pitx1 = no limb = not sufficient
conditonal ko of tbx5 then rescue with tbx4 and pitx1 = partial hl therefore both imp for fl id

29
Q

what signalling pathway group do fgf belong to ?

A

tyrosine receptor kinases