Practice question

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.