Regulation Of Specific Gene Expression Research Articles

Hormonal regulation of specific gene expression

Hormonal regulation of specific gene expression

Steroid Hormone Regulation of Specific Gene Expression

This chapter describes the steroid hormone regulation of specific gene expression. A large number of proteins have been reported to increase in concentration or activity after steroid hormone treatment. In the chick, the administration of estrogen induces growth and differentiation and the synthesis of a number of egg white proteins, the major one of which is ovalbumin. The weight of the oviduct increases several hundredfold, and there is a massive proliferation of tubular gland cells. The oviduct proteins regulated by estrogen include conalbumin, ovomucoid, and lysozyme. The synthesis of these proteins, however, is not strictly coordinated, and each is synthesized more or less independently in response to estrogen. The rapidity of the vitellogenin response and the absence of any detectable vitellogenin messenger RNA (mRNA) in the untreated liver in both the xenopus and the rooster suggest a primary effect at the transcriptional level. The anamnestic response, on the other hand, is an observation that could be explained by a persistent change in the conformation of the vitellogenin gene and a permanent change in the estrogen-receptor generation or response.

Nuclear proteins of rat liver and of an aminoazo‐dye‐induced hepatoma

Nuclear proteins of rat liver and rat ascites hepatoma were fractionated by extraction in solutions of different salt concentration and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The difference between the electrophorograms of the different fractions of nuclear proteins isolated from liver and from hepatoma was found in the bands which have the same electrophoretic mobility as the main proteins of informofers and are extracted from nuclei at salt concentrations which extract informofers. These changes in the electrophoretic patterns of proteins with the solubility and mobility of the proteins of informofers could be related to the defective processing of heterogeneous nuclear RNA in the hepatoma. In addition the identity of electrophorograms of nuclear proteins isolated from liver and from hepatoma and the identity of most bands in the electrophorograms of nuclear proteins which are soluble in 0.35 M NaCl and chromosomal proteins which are not soluble at this salt concentration support the notion that these nonhistone nuclear proteins which can be identified as the major bands in electrophorograms of chromosomal proteins are not the specific regulators of gene expression.

Regulation of specific gene expression during embryonic development: Synthesis of globin messenger RNA during red cell formation in chick embryos

Globin mRNA from chick red blood cells at various stages of embryonic development have been isolated and characterized physically and functionally by translation in a cell-free system. Also described is the preparation and use of “cDNA” complementary to mRNA in the study of globin mRNA synthesis during the early stages of erythroid cell differentiation.

Mechanisms of hormonal induction of enzymes

The study of enzyme induction by hormones has provided an important experimental model for the investigation of both the molecular mechanisms of hormone action as well as the regulation of specific gene expression in higher organisms. The exact mechanisms by which hormones induce enzymes are as yet unknown. The ability to study enzyme induction in relatively simple experimental systems such as cells in tissue culture allows the investigator to assess unequivocally the role of single hormones and to pose mechanistic questions. It is hoped that advances in genetic approaches to enzyme induction will accelerate progress in understanding these mechanisms. Studies of tyrosine aminotransferase induction by glucocorticoids in the HTC cell system have led to a model of enzyme induction in which the inducing steroids are thought to antagonize the action of a posttranscriptional repressor. The emphasis of this model, in contrast to those based on bacterial models, is that regulation of specific gene expression need not operate at the genetic or transcriptional level; i.e., by stimulating specific mRNA synthesis. Transcripitonal controls surely exist in animal cells, but their role in specific enzyme induction remains to be established. In addition to glucocorticoids, several other hormonal factors including insulin, a macromolecular factor in serum, and dibutyryl cyclic-AMP, can also enhance TAT synthesis, all probably affecting separate and distinct posttranscriptional steps in the synthesis of a single protein.