1 Limb development Flashcards
What are the three germ layers?
Ectoderm.
Mesoderm.
Endoderm.
How do the limb buds form?
Core derived from lateral plate mesoderm. Covered by ectoderm. Mesoderm core differentiate into mesenchyme.
What does the paraxial mesoderm form either side of the neural tube?
Somites.
Describe somite differentiation:
Ventral - sclerotome - vertebral column.
Dorsolateral - dermomyotome - divides - dermis and skeletal muscles.
Describe myotome differentiation:
Dorsal epimere - back muscles.
Ventral hypomere - muscles of thoracic + abdo wall.
The ventral hypomeres migrate to the limb buds and form:
Posterior condensation.
Anterior condensation.
When does limb rotation occur?
What is the rotation?
6-8 weeks.
Upper: 90o laterally.
Lower: 90o medially.
How is proximodistal limb growth controlled?
Lateral plate mesoderm secretes fibroblast growth factor (Fgf 10).
This induces apical ectodermal ridge (AER). AER secretes Fgf 4+8. Cause proliferation in progress zone.
How is dorsoventral patterning controlled?
Dorsal ectoderm expresses Wnt7.
Ventral ectoderm expresses Engrailed-1, inhibiting Wnt7.
How is craniocaudal patterning controlled?
Zone of polarising activity (ZPA) expresses sonic hedgehog (Shh). this diffuses cranially. High conc induces caudal structure formation.
When and how does digit formation occur?
Week 6.
Apoptosis in AER splits it into 5.
Differentiate between Amelia and Meromelia.
Amelia: complete absence of limb.
Meromelia: partial absence of limb.
What is phocomelia?
Example teratogen?
Premature digit development and proximal limb missing.
Thalidomide inhibits Fgf 10+8.
Differentiate between syndactyly, polydactyly and ectrodactyly:
Syndactyly: fused digits.
Poly: extra digits (too much Shh).
Extra: split hand/foor - failure of AER formation.
