Lecture 1: Limb Development Flashcards
limb field definition
hox genes determine in which position each of the 4 limb buds will form in vertebrates
what substance plays an important role in initiating limb bud outgrowth
retinoic acid
what 4 developmental tissues/cells give rise to forelimb and hindlimb
ectoderm
dermatome
myotome
somatic lateral plate mesoderm
what determines the timing of limb development
different hox genes expressed at different times
how do limb elements develop (in what direction)
proximal to distal
T box genes determine
limb identity (pectoral vs thoracic)
what do hox genes determine (2)
where limb buds will form
what limb will develop at specific location
what forms the core of the limb field
mesenchyme (undifferentiated tissue)
3 early development steps: limb field to limb bud
induction of limb development –> establishment of AER and ZPA signaling centers –> promotion of outgrowth and patterning in established limb bud
origination of limb buds (what/where)
ridges in ventrolateral body wall
2 types of limb buds
forebud
hindbud
which limb bud develops first
forebud
3 axes where limbs develop simultaneously
proximodistal
dorsoventral
craniocaudal
AER/apical ectodermal ridge: definition
thickened, specialized epithelium
what does AER induce proliferation of
limb bud mesenchyme through progress zone
progress zone: definition, function
area of mesenchyme just proximal to AER
encourages growth
proximodistal axis determined by
fibroblast growth factor acting at the AER
dorsoventral axis determined by
non AER dorsal ectoderm
folding initiated by Wnt7a
craniocaudal axis determined by
sonic hedgehog genes acting at zone of polarizing activity
feedback loop of limb development and continued AER growth
lateral plate mesoderm expressing fibroblast growth factors to create more growth at AER
what happens to each limb bud once acquiring terminal length
terminal portion flattened to form hand and foot plates
what divides portion of each limb bud once they’ve become hand and foot plates
2 constrictions
proximal-distal development steps (3/4)
formation of hand and foot plates
2 constrictions
limb bud with 3 main segments = stylopod, zuegopod, autopod
mesenchyme condenses into cartilage for future long bones
stylopod
arm/thigh
zeugopod
forearm/leg
autopod
hand/foot
what directs pattern formation in dorsal ventral axis
non AER ectoderm
what gene expression initiates limb forming interactions between ectoderm and mesoderm
Fgf 10
how are final constrictions and separation of digits formed (what process)
apoptosis/programmed cell death
dorsal and ventral aspects of limb follow what process
lateral folding of embryo
what is dorsal-ventral axis important for
patterning muscles
where does D/V (dorsal/ventral) center reside
dorsal ectoderm
result of AER signaling in cranial-caudal axis
Shh (sonic hedgehog) expression and formation of ZPA
what is the origin of all nerves
ventral primary ramus
what nerves follow growing muscle and provide motor innervation
ventral and dorsal branches of ventral ramus
what cells express retinoic acid and sonic hedgehod
ZPA cells
what 2 inputs are required for ZPA and sonic hedgehog expression
AER
dorsal ectoderm
homology definition
existence of shared ancestry between a pair of structures or genes in different species
pentadactyl limb
ancestral 5 digit condition
digit reduction is the result of what
species specific evolutionary history
2 types of patterning changes of cell death
patterning
post patterning
post patterning changes: starting condition, order to digit reduction
initial limb segments laid out in cartilage
digits I and V eliminated
digits II and IV reduced
what 2 mammals have post patterning changes
horses
camels
patterning changes: starting condition, order of digit reduction
never start with a pattern
digit loss and shift of central axis of foot between digits III and IV (loss occurs at SAME time as pattern formation)
order to digit loss
I, V, II, IV
what directions do forelimb and hindlimb rotate leading to final limb position
forelimb rotates dorsally
hindlimb rotates ventrally
Cingulum, stylopodium, zeugopodium and autopodium in forelimb
Scapula and clavicle —> humerus —> radius and ulna —> carpal bones, metacarpal bones and phalanges
Cingulum, stylopodium, zeugopodium and autopodium in hindlimb
Ox coxae/hip (ileum, pubis, ischium) —> femur —> tibia and fibula —> tarsals, metatarsals and phalanges
