Activation of Cell-Specific Expression of Rat Growth Hormone and Prolactin Genes by a Common Transcription Factor

In the anterior pituitary gland, there are five phenotypically distinct cell types, including cells that produce either prolactin (lactotrophs) or growth hormone (somatotrophs). Multiple, related cis-active elements that exhibit synergistic interactions appear to be the critical determinants of the transcriptional activation of the rat prolactin and growth hormone genes. A common positive tissue-specific transcription factor, referred to as Pit-1, appears to bind to all the cell-specific elements in each gene and to be required for the activation of both the prolactin and growth hormone genes. The data suggest that, in the course of development, a single tissue-specific factor activates sets of genes that ultimately exhibit restricted cell-specific expression and define cellular phenotype.