Overview Gene Function Sonic hedgehog (SHH) Involved in patterning along anterior-posterior axis Embryonic development of limbs, somites, gut formation and establishment of midline CNS produced in zone of polarizing activity (ZPA: collection of mesoderm cells at posterior border of apical ectodermal ridge on developing limb) secreted by notochord to control neural tube patterning Mutation in SHH pathway and/or haploinsufficiency can lead to holoprosencephaly, a developmental defect characterized by a failure of the early forebrain vesicle to divide into distinct halves WNT-7 Necessary for proper organization alongdorsal-ventral axis Development of midbrain and limb patterning produced at dorsal apical ectodermal ridge (AER: thickened ectoderm at distal end of each developing limb) FGF Stimulates mitosis and differentiation of underlying mesoderm provides for lengthening of limbsby maintainingprogress zone(progress zone: proliferating mesenchymal cells proximal to AER) produced atapical ectodermal ridge Controls anterior-posterior neural tube patterning Plays a role in somite segmentation, angiogenesis, and axon growth Homeobox(HOX) Involved in segmental organization in cranio-caudal direction production depends on combinatorial expression of SHH, WNT-7, and FGF controls rib development, cardiac patterning, and radioulnar differentiation of the upper extremity