Practice question

Hindlimb initiation and distal patterning integrate Tbx4-Pitx1 selector program with posterior Hox inputs. While Tbx4 and Pitx1 are primary determinants imposing leg identity, posterior distal Hox genes such as Hoxd13 reinforce hindlimb autopod expansion, digit morphogenesis, and maintenance of hindlimb-specific enhancers downstream of Pitx1. Pitx1 activates Tbx4 and represses forelimb program, FGF10 initiates outgrowth, Tbx5 marks forelimb. Among provided choices, Hoxd13 represents distal hindlimb patterning component linked to hindlimb stylization, consistent with its posterior-restricted function in leg morphogenesis and digit development.