Development of limbs Flashcards
What is the origin of muscle in the extremities
paraxial mesoderm –> somite
dermamyotome –> myotome –> hypomere –> dorsal lateral hypomere cells migrate to limbs
What is the fate of migrating hypomere cells
become dorsal and ventral muscle masses
what is the fate of the dorsal muscle mass?
becomes extensors/supinators/abductor muscles of the limbs
what is the fate of the ventral muscle mass?
becomes flexors/pronators/ abductors
What are the tendons and bones of the extremities derived from?
the lateral plate mesoderm
know this cause it was highlighted heavily on slides
how is bone in the extremities formed? when does it begin
lateral plate mesoderm begins the process of endochondral ossification during week 5
What happens during week 5 6 and 7-9 during bone formation
week 5-begins
week 6-limb cartilage forms
week 7-9-osteogensis creating long bones
When do limb buds appear?
week 4
When does the hand/foot plate appear as well as the beginning of chondrification?
week 5
When do the digital rays of the hand form? also limb skeleton is cartilaginous
week 6
when do the digital rays of the feet form?
week 7
when does osteogenesis take place?
week 7
when does limb rotation occur
week 7
when are separate digits formed?
week 8
what occurs during week 12?
primary ossification
What direction are the limbs facing before rotation?
ventral surface facing medially
dorsal surface facing laterally
What occurs during rotation of the upper limb?
rotates laterally so flexor compartment faces anteriorly and extensor faces posteriorly
what occurs during rotation of the lower limb?
rotates medially so flexor compartment faces anteriorly and extensor faces posteriorly
What week do axons from ventral rami innervate muscle? what is this followed by?
week 5
sensory axons follow it
NCC turned schwann cells myelinate it
What muscles do axons cranial to the limb innervate?
dorsal muscles
What muscles do axons caudal to the limb innervate?
ventral muscles
blood supply
idk look it up cause i dont get it
What are the 3 parts of the growing arm? which is proximal which is distal?
stylopod –> zeugopod –> autopod (proximal to distal)
What is secreted by lateral plate mesoderm that begins the process of budding?
Fgf10
What does Fgf10 do?
activates WNT signaling, promotes distal extension of AER and causes it to secrete Fgf8
What occurs when WNT signaling is turned on?
AER secretes FgF8 –> positive feedvack loop for more Fgf10
what is the AER?
apical ectodermal ridge (part that moves distally during budding)
What occurs if you remove the AER?
no limb growth
what happens if you have extra AER?
extra limb growth, winging
what happens if you replace arm mesenchyme with leg mesenchyme but keep the AER intact?
you get a normal leg where the arm is supposed to be
what happens if you replace arm mesenchyme with non limb mesenchyme?
AER regresses and nothing grows
what happens if you replace AER with an FGF bead?
normal limb growth
What causes differentiation into the 3 sections? what happens if one of these is knocked out?
HOX genes, if the HOX gene is knocked out that part doesnt form
What is the HOX gene for the sytlopod?
HOX 9-10
What is the HOX gene for the zeugopod?
HOX11
What is the HOX gene for the autopod?
HOX12-13
What causes a limb to differentiate cranial from caudal?
a ZPA region that is present before budding occurs
What does the ZPA region secrete? what does this do?
SHH, causes pinky formation, as you move down the gradient it causes other fingers to form
What happens if you have too much SHH or an extra ZPA region?
polydactyly (multiple fingers) usually an extra pinky
You have an extra pinky. What was there too much of during your development?
SHH secreted from the ZPA region
You knocked out HOX9-10, what doesnt form,?
stylopod
you knocked out HOX11, what doesnt form?
zeugopod
You knocked out HOX12-13 what doesnt form
autopod
What causes dorsal vs ventral differentiation?
Lmx1B activates Wnt7a that causes dorsal differentiation
How do you form individual digits?
BMP signaling causes apoptosis in cells between digits
You have decreased BMP expression and are now a good swimmer, why is this?
you have webbed fingers you freak (syndactyly)
What is meromelia and what causes this?
absence of PART of a limb
late or partial loss of FGF signaling
what is amelia? cause?
total loss of a limb
early or complete loss of FGF signaling
What is polydactyly? cause?
extra digits (usually pinky) over-expression of SHH, lacks muscle tho
What is syndactyly? types? cause of each?
fusion of digits
cutaneous (lack of BMP)
osseous (bones, fuse) BMP or HOXD13 mutation
what is phacomalacia?
absence of long bones
what causes phacomalacia that is no longer given to females of child bearing age?
thalodimide
What does thalodimide do?
decreases FGF or HOX signaling
what causes split hand/lobster claw/ectrodactyly?
decreased FGF8 expression in part of the AER but the rest remains so its split
what can cause physical deformities?
adhesion between amnion and fetal structures, club foot and stuff
