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#autopod

3 public questions tagged with this topic.

Limb Development -ll

Which molecule determines digit identity in the autopod?

Autopod digit patterning and identity along anterior-posterior axis depend on posterior-derived Sonic Hedgehog gradient from ZPA. Duration and concentration of SHH exposure differentially regulate Gli3 processing from repressor to activator and 5-prime HoxD expression, specifying digit one thumb anteriorly through digit five little finger posteriorly with distinct sizes. High prolonged SHH maintains posterior Hoxd13 and posterior identity, low transient yields anterior. BMP4 sculpts interdigits through apoptosis, Wnt3a governs dorsal-ventral polarity, TBX5 governs forelimb field. Thus SHH determines which morphological digit character forms in autopod and controls number.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: SHH determines digit identity.

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Limb Development -lll

Which Hox genes are primarily responsible for specifying the autopod?

Proximal-distal patterning follows temporal colinearity of HoxA and HoxD clusters. Early-expressed Hox9 paralogues mark stylopod progenitors forming humerus and femur, intermediate Hox10-11 specify zeugopod radius ulna tibia fibula, while late 5-prime genes Hox12 and Hox13 are activated distally under prolonged FGF exposure and repressed proximally by retinoic acid and Meis factors. Combined Hoxa13 and Hoxd13 activity is essential for autopod wrist ankle and digits. Deletion abolishes digits, whereas Hox9 or Hox11 mutants affect proximal segments, definitively defining autopod genetic code.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: Hox12-13 specify autopod patterning.

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Tetrapod

Which transcription factor is necessary for specifying the autopod?

Autopod encompassing carpals, tarsals, metapodials and digits is specified by distal Hox genes HOXA13 and HOXD13 activated during late phase after Hox11 downregulation. Hoxa13 deficient mice display hypoplastic carpals, absent distal condensations, fused digits. These transcription factors regulate EphA7, Sost, and BMP antagonists to establish hand-plate and digit periodicity. Enhancer topology at HoxA/D clusters switches from proximal to distal regulation via 5' enhancers. Therefore HOXA13 serves as definitive transcription factor necessary for autopod identity, distinguishing hand-foot from more proximal arm-leg segments.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: HOXA13 requirement for autopod specification and patterning.

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