Podlasek, C.A.: POSTERIOR HOX GENE EXPRESSION IN DEVELOPING GENITALIA

The process of development requires complex interactions of mesenchyme and epithelium to specify tissue identity and unique organ specific morphology. The Hox family of homeobox genes encode transcriptional regulators that are crucial for specification of positional identity during embryogenesis and which are expressed in a colinear manner in regionalized domains along the main body axis, limb, lung, and gut. Conserved mechanisms of gene expression and regulation are apparent during embryogenesis and postnatal morphogenesis of these organ systems, with minimal variation evident across species. A rudimentary pathway of essential developmental genes has been defined in the limb, which includes both positive and negative growth regulators such as Hox genes, Sonic hedgehog (Shh), and Bone morphogenetic proteins 2 and 4. These same genes are abundantly expressed in the primary and accessory sex organs during development and targeted loss of a specific member of the pathway results in genital abnormalities. It is proposed that vertebrate genitalia represent another developmental axis, similar to the limb, and that mechanisms that define positional identity and control proliferation in the limb, lung and gut are also crucial for normal specification and morphogenesis of the primary and accessory sex organs.