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#body axis

2 public questions tagged with this topic.

Limb Development -l

Which factor ensures proper positioning of the limb bud along the body axis?

Proper positioning of limb buds along rostrocaudal axis is instructed by combinatorial Hox gene expression in lateral plate mesoderm encoding limb field location. Hox4-Hox5 paralogs define cervical region, Hox6-Hox9 cervicothoracic transition permits Tbx5 activation for forelimb, Hox10-Hox11 lumbosacral region permits Tbx4 and Pitx1 for hindlimb. Transplanting lateral plate mesoderm retains Hox-encoded positional memory forming limb at ectopic site with original Hox identity. Wnt3a initiates ridge, BMP4 regulates apoptosis, Pax6 controls eye, confirming Hox genes as axial blueprint coordinating limb emergence at somitic levels.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Hox genes axial positioning of forelimb and hindlimb fields.

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Regeneration -l

Which factor is responsible for inducing the formation of a new body axis in hydra?

Induction of supernumerary body axis requires ectopic organizer activity capable of redirecting surrounding tissue. In Hydra this occurs when Wnt3 is experimentally upregulated in gastric column via transgenesis or lithium chloride activating beta-catenin. Small cluster of Wnt3-expressing cells autoactivates downstream organizer genes including Brachyury, goosecoid, and BMP inhibitors, establishing new oral pole that evaginates tentacles and forms second hypostome. SHH homolog absent, beta-catenin is intracellular effector not secreted inducer, Pax6 controls eye specification. Thus Wnt3 ligand itself acts as primary axis-inducing morphogen initiating positive feedback loop that generates long-range patterning and complete secondary head structure during budding and regeneration.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Wnt3 induces new body axis in Hydra budding and regeneration.

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