Practice question

Morphological distinction between forelimb and hindlimb including muscle, tendon, bone patterns is orchestrated by Pitx1 homeodomain factor restricted to posterior lateral plate mesoderm and hindlimb buds. Pitx1 directly activates Tbx4, Hoxc10, and influences cell adhesion, cartilage nodule organization. Transgenic misexpression of Pitx1 in forelimb induces hindlimb-like musculature and skeletal transformations, upregulates hindlimb markers, whereas Tbx4 misexpression alone insufficient for full conversion. Pitx1 knockout causes hindlimb to acquire forelimb-like features including patella loss. Thus Pitx1 functions as master determinant distinguishing hindlimb identity.