Limb Development Flashcards
Why are limbs important?
To break it down in da club after QUARANTINE!
When do upper and lower limb buds form?
4th week
Upper - 24 days
Lower- 25-26 days
What is the apical ectodermal ridge (AER)?
What happens there?
A thick band of ectoderm where limb buds form.
Mesenchyme proliferate and grow from ateral plate mesoderm (limb buds now bulge)
Regions of limb outgrowth
Stylopod- humerus or femur
Zeugopod- radius and ulna; tibia and fibula
Autopod- hands/ feet
Axes of limb bud?
Proximal-Distal (Shoulder-Digits) FGF signalling & HOX
Cranial-Caudal (Hallu- Phalanx V) SHH & HOX
Dorsal-Ventral (Dorsum-Palm) Wnt7a and Engrailed (En1)
What growth factor induces AER?
FGF10
What does AER secrete?
FGF8 (bc positive feedback from FGF10)
FGF and AER make what axis?
Proximodistal
Manipulating AER (early, late, and transplant)
Early removal: only 1st segment
Late removal: 1st and 2nd segments
Transplanting: supernumerary digits
Meromelia
‘partial-limb’
intermediate to late loss of FGF
Amelia
‘no-limb’
early loss of FGF signaling
Phocomelia
‘seal’s-limb’ loss of long bones
Partial loss of FGF signalling
OR thalomide disrupting HOX
**thalomide used to be taken during pregnancy
Adactyly
Absent digits
Late loss of FGF
Ectrodactyly
Split hand. ‘Lobster claw’
Partial absense of FGF8 from AER
1.5:100,000
(EEC)- ectrodactly- ectodermal dysplasia, cleft palate
Zone of Polarizing Activity (ZPA) makes ___ axis?
By expressing what?
craniocaudal
SHH
What digit is most likely to form in absence of SHH?
Digit 1 (cranial end)
How does Polydactyly occur?
Overexpression of SHH causes 2nd ZPA to form (now in cranial and caudal end)
Extra digits lack normal musculature