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#SHH

8 public questions tagged with this topic.

Regeneration -l

What is the role of SHH in limb regeneration?

Sonic hedgehog family member secreted from posterior mesenchyme establishes anterior-posterior pattern in developing and regenerating limbs. During salamander and chick limb regeneration, SHH expressed in posterior blastema activates downstream Gli transcription factors, with gradient high posteriorly specifying digit five to four to three identities and low anterior leading to thumb. Ectopic SHH beads anteriorly duplicate digits mirror-symmetrically, while SHH blockade produces digit loss and shortened limbs. Beyond digit specification SHH promotes cell cycle progression and survival of blastema cells, regulates blood vessel formation secondarily, but canonical role is promoting digit formation and posterior pattern rather than suppressing growth.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: SHH in limb regeneration - ZPA and digit specification.

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Tetrapod

Which axis is specified by the interaction of SHH and the AER?

Anterior-posterior axis specification depends on coordinated interaction between posterior SHH from ZPA and distal FGFs from AER. FGF signals maintain SHH expression via Gremlin1-mediated BMP antagonism, while SHH maintains FGF expression. Duration and strength of this SHH-FGF-Gremlin feedback loop encodes positional information along AP axis, controlling digit number and identity via Gli3 activator/repressor balance and Hand2 induction. Removal of either center prematurely truncates pattern, while ectopic graft prolongs signaling causing duplications. Hence AP axis emerges from integrated SHH and AER cross-talk rather than independent single signal.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: SHH-FGF interaction specifying anterior-posterior axis.

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