Peptide hormone gene expression in heterogeneous tissues — The pro-opiomelanocortin system

The pro-opiomelanocortin (POMC) gene which codes for a polyhormone protein is regulated differentially in the lobes of the pituitary. The expression of the POMC gene can be modulated at the level of transcription, processing of heteronuclear RNA, and stabilization of messenger RNA. With recombinant DNA technology and the newly developed in-situ hybridization histochemistry, this system can be used advantageously in the study of peptide hormone gene regulation. Data obtained thus far point out two different types of regulation: gene activation or inactivation in corticotrophs and/or the change in number of POMC-producing cells. This paper will focus on the new approaches which may enable one to distinguish between the regulation of gene expression and the differentiation of cells due to hormonal induction.