Developmental pathways: Sonic hedgehog-Patched-GLI.

Developmental pathways are networks of genes that act coordinately to establish the body plan. Disruptions of genes in one pathway can have effects in related pathways and may result in serious dysmorphogenesis or cancer. Environmental exposures can be associated with poor pregnancy outcomes, including dysmorphic offspring or children with a variety of diseases. An important goal of environmental science should be reduction of these poor outcomes. This will require an understanding of the genes affected by specific exposures and the consequence of alterations in these genes or their products, which in turn will require an understanding of the pathways critical in development. The ligand Sonic hedgehog, the receptors Patched and Smoothened, and the GLI family of transcription factors represent one such pathway. This pathway illustrates several operating principles important in the consideration of developmental consequences of environmental exposures to toxins.