090914 dev of limb Flashcards
limb precursor tissues
limb mesenchyme (somatic mesoderm, somitic mesoderm which is from the somite and forms the abaxial compartment)
surface ectoderm
limb development times differ btwn upper and lower limb by
upper limb is ahead of lower limb by 1-2 days
when does establishment of the limb field occur?
week 4
budding is an inherent property of
mesoderm-the somatic mesoderm
apical ectodermal ridge
ectoderm thickening at dorsal and ventral interface
what occurs during wks 5-9 w/ regards to limb development
elongation of the limb
tissue formation and organization
what does elongation result from?
epithelial-mesenchymal interactions at the AER and mesoderm interface
differentiation occurs in what direction
proximal to distal
time wise, how does limb development occur in each of the three axes?
simultaneous along all three
how does development along the proximal distal axis occur
ectoderm and mesoderm reciprocally signal to each other (Fgf 10, Fgf 8)
proximally, there’s more retinoic acid and distally, there’s more Fgf and Wnt (molecule gradients)
roles of the mesenchyme
induces and sustains AER
determines whether it’s upper or lower limb
roles of AER
maintains proliferating pool of mesenchyme with Fgf8
maintains ZPA
interacts with proximal-distal and anterior-posterior specific proteins to give mesenchymal cells positional information
if you remove the AER what happens
elongation stops; limb is truncated
amelia
no limb
meromelia
partial limb
congenital constrictive band syndrome
when amniotic bands tighten around body parts
failure of formation of parts in the transverse direction
amputation along the proximal distal axis
a failure of communication btwn AER and mesoderm
what controls anterior posterior patterning
zone of polarizing activity (ZPA), which is at the posterior border of the limb
sonic hedgehog (shh)- (retinoic acid also has the same effect). if provide retinoic acid bead, you get more digits forming along A-P axis
gradient of Shh causes Hox gene combinatorial expression
failure of formation of parts in lognitudinal direction
amputation along A-P axis
phocomelia
shortened limbs-along A-P axis
seal hands
phocomelia
linked often to thalidomide drug exposure
what role does apoptosis play in limb development
separation of digits
absence of distal phalanx of large digit
the apoptosis is caused by disappeared of the AER
syndactyly
when digits are fused due to failure of separation
sirenomelia
legs are fused together developmentally
development along the dorsal ventral axis influences what?
skeletal muscles (myoblasts organize into dorsal and ventral premuscle masses)
neural and vascular structures
limb compartmentalization
mediators of dorsal ventral patterning
factors like Wnt 7a
transcription factor En
sprengel deformity
scapula descended in devleopment when it shouldn’t have
cleidocranial dysplasia
abnormal development of limb girdles
missing clavicle
talipes equinovarus
turned in hindfoot
adduction of forefoot
plantar flexion of foot
significant crease in instep
unknown what causes it
what is the critical period for limb development
wk 4-9
somatic mesoderm gives rise to
dermis and connective tissue
