Transcriptional Control of GH Expression and Anterior Pituitary Development*

Abstract

I. Introduction CASCADES of interacting regulatory genes controlling developmental pathways have been defined in organisms such as Drosophila (1–9) and the nematode Caenorhabditis elegans (10–12). The developmental regulators include transcription factors, kinases, phosphatases, growth factors,receptors, and cell-adhesion molecules. In Drosophila, products of maternally expressed genes control expression of zygotic segmentation genes, the products of which regulate homeotic gene expression; regulation is also exerted between genes of the same class. As a result, the embryo is divided into a meshwork of metameric units, each expressing a unique combination of homeotic genes. These genes contain a conserved homeobox, encoding a 60-amino acid homeodomain which functions in DNA binding. By acting as transcription factors, the homeodomain proteins orchestrate activation of a unique combination of target genes which makes the cells enter a specific morphogenetic pathway. The molecular mechanisms underlying regu...