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#limb specification

2 public questions tagged with this topic.

Limb Development -l

Which region of the limb is specified by Hoxa11 expression?

Segmental identity along proximodistal axis maps onto nested HoxA and HoxD cluster expression. Hoxa11 paralog specifically marks middle segment zeugopod encompassing radius and ulna in forelimb and tibia and fibula in hindlimb. Hoxa9-Hox10 dictate stylopod humerus-femur, Hoxa13 defines autopod wrist and digits. Compound Hoxa11 and Hoxd11 double mutants develop severely truncated dysmorphic zeugopod with fusions, while stylopod remains less affected. This precise mapping demonstrates temporal collinearity driving segmental limb architecture through Hox-controlled proliferation and differentiation programs and growth timing. Conserved across chick mouse human models, this mechanism illustrates classic embryological principles integrated with modern molecular genetics.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Hoxa11 and Hoxd11 – zeugopod specification and knockout phenotype.

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Limb Development -l

Which homeobox gene family controls stylopod, zeugopod, and autopod specification?

Proximal-distal regionalization into stylopod humerus-femur, zeugopod radius-ulna-tibia-fibula, and autopod hand-foot is governed by nested HoxA and HoxD clusters obeying spatial and temporal collinearity. Hox9 and Hox10 paralogs expressed early proximally confer stylopod identity, Hox11 marks zeugopod, Hox12-Hox13 mark autopod including carpals-tarsals and digits. Pax genes control eye and dermomyotome, Wnt governs dorsoventral axis, TGF-beta modulates growth broadly. Loss of specific Hox paralogs causes segment-specific deletions and homeotic transformations, confirming Hox code assignment of segmental identities and timing. Conserved across chick mouse human models, this mechanism illustrates classic embryological principles integrated with modern molecular genetics.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Hox genes collinearity – stylopod, zeugopod, autopod specification.

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