Making a Limb Bud Flashcards
What day is the body plan established in chicks
day 2
Describe the body plan of a homozygous hox5b knockout mouse
forelimbs develop at more anterior level
What do hox genes restrict
expression of fibroblast growth factors
What are fibroblast growth factors required for
limb bud outgrowth
What do hox genes control
where FGF is expressed
What are FGFs
secreted signalling molecules
What happens to homozygous knockout mice of FGFs
embryos lack limb buds
What is the function of FGFs
sufficient and required for limb bud formation
Describe the effect of a local application of FGF to a chick
Forms an ectopic limb bud which expresses sonic hedgehog
Describe the apical ectodermal ridge in chicks
rigid ridge of thickened epithelium around lip of limb bud
What is the function of the apical ectodermal ridge
maintains progress zone, important in developing limb
What does removal of the apical ectodermal ridge cause
truncation of the limb - but some patterning still continues
What does the apical ectodermal ridge secrete
signalling molecules
What can substitute for the AER
FGFs - which restore near normal growth
Where is the progress zone located
most distal region of limb bud
what are the cells in the progress zone derived from
mesoderm
Describe the cells in the progress zone
undifferentiated rapidly dividing cells
What does the length of time the cells stay in the progress zone determine
cell fate along the proximal-distal axis
What experiment tests the role of the progress zone
heterochronic graft
Describe the zone of polarising activity
region of posterior limb bud mesenchyme
What is the effect of transplanting the ZPA underneath anterior AER
induces symmetrical duplications of limb about the AP axis
What does the ZPA form
AP axis of limb
Where is sonic hedgehog mRNA expressed
Zone of polarising activity
What happens when sonic hedgehog mRNA is translated
influences pattern across whole limb bud
what is shh
morphogen
Is shh necessary or sufficient to pattern axis of limb
sufficient
Describe the expression of shh
very localised to ZPA
Which region of the limb bud acts as an organising centre
ZPA
What type of signal is shh
long range signal
What is needed for the formation of digits
apoptosis, programmed cell death, differential growth & proliferation
What germ layer determines the pattern of cell death
mesoderm
