Lecture 1: Limb Development Flashcards
stylopod
humerus
femur
zeugopod
ulna and radius
tibia and fibula
autopod
wrist and fingers
ankle and toes
what cells gives rise to the fore and hind limb
- ectoderm cells
- hypaxial part of myotome
- somatic part of lateral plate mesoderm
what does the lateral plate mesoderm give rise to
cartilage, bone, CT
what does the paraxial mesoderm give rise to
somites and skeletal muscle
what does the ectoderm give rise to
out pocketing of ventral body wall: epidermis of skin, hair, nails
spinal nerves form nervous plexuses
what determines the timing of limb development
Hox genes
- determine where limb bud will form and what limb will develop where
what is the role of T-box genes in limb development
they have a role in limb identity
what occurs at the limb field
induction of limb development
establishment of AER and ZPA
what transcription factors induce formation of the limb bud
fibroblast growth factors
T-box transcription factors
where do limb buds originate
as ridges in the ventrolateral body wall
the forebud ridge appears first, followed by ?
hindbud ridge
what 3 axes do the limbs develop along simultaneously
proximodistal
dorsoventral
craniocaudal
at what growth axis does the apical ectodermal ridge (AER) direct pattern formation
proximal distal axis
what is the progress zone (PZ)
area of mesenchyme (undifferentiated tissue) proximal to the AER
what induces proliferation of the limb bud mesenchyme
AER
limb development depends on the interaction between what two components
limb bud mesenchyme and apical ectodermal ridge
the terminal portion of each limb bud becomes flattened to form ______
hand and foot plates (that eventually become fore and hindlimb)
two constrictions divide the limb bud into what 3 main segments
stylopod (arm/thigh)
zeugopod (forearm/leg)
autopod (hand/foot)
the dorsal-ventral axis follows what folding pattern
the lateral folding of the embryo
what directs the pattern of formation of the cranial-caudal axis
the zone of polarizing activity (ZPA) = area of mesenchyme
what do ZPA cells express
sonic hedgehog (Shh)
The ZPA (and Shh expression) requires input from what two things
input from apical ectodermal ridge (AER) and the dorsal ectoderm
essentially the ZPA doesn’t work alone
final limb morphology is the product of ?
apoptosis
what is the role of AER in the number of digits and limb segmentation
AER breaks up and only covers emerging digital rays
interdigital spaces lose AER and are sculpted by apoptosis
what is the pentadactyl limb
the ancestral 5-digit condition
is digit loss random
no, it follows a pattern
the final position of the limbs is a result of what
limb rotation
forelimb rotates dorsally
hindlimb rotates ventrally
what induces myoblasts to migrate out from somites and enter the limb bud
lateral plate mesoderm
how is the apical ectodermal ridge formed
by interaction of fibroblast growth factors that create a feedback loop to maintain growth
