Hormonal Regulation of Casein Gene Expression in Normal and Neoplastic Cells in Murine Mammary Glands

Abstract

Contemporary advances of knowledge and technology in the areas of cellular and molecular biology have revealed that selective gene expression plays a definitive role in the regulation of cellular differentiation. In conventional terms, selective gene expression denotes a regulated transcription of different structural genes producing the respective mRNAs. During recent years it has also become evident that the physical structure of eukaryotic genes are composed of expressed (exons) and unexpressed (introns) segments along the DNA strand and this requires splicing and processing of the initial transcripts into the final mRNA (20), (50), (119). Moreover, post-translational processing of the polypeptides may also modify the final product and hence influence gene expression (108). Thus, selective gene expression during a developmental process may be subject to modulation at any of these complex series of events. Based on the observation that the insect steroid hormone, ecdysone, is capable of inducing specific puffs in polytene chromosomes of Drosophila larvae, Karlson (55) proposed that hormonal modulation of specific gene expression may influence developmental processes in the target tissue. Demonstration of ecdysone-induced synthesis of the enzyme, dopa decarboxylase in the larvae (101), correlation between transcription and puff formation in the polytene chromosomes (31), and cell-free translation of ecdysone-induced mRNA for dopa decarboxylase (56) now appear to corroborate Karlson’s original thesis.