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The mechanism by which prolactin, a peptide hormone, regulates casein gene expression has been studied in mammary gland organ culture. After prolactin addition, a 2-4 fold increase in the rate of casein mRNA transcription was observed within 1 hr and maintained for at least 24 hr. This increased rate of transcription is not sufficient to account for the mass accumulation of casein mRNA. The half-life of casein mRNA is also increased 17-25 fold in the presence of prolactin. This change in casein mRNA half-life, coupled with a 2-4 fold increase in the rate of transcription, can account for the normal accumulation of casein mRNA observed after prolactin addition. This hormone-induced change in casein mRNA half-life appeared to be selective, since prolactin was found to exert only a slight effect (1-4 fold) on the half-life of poly(A) RNA determined under identical pulse-chase conditions. The hormonal regulation of casein gene expression thus does not app-ar to be an "all or none" process occurring only at the transcriptional or post-transcriptional levels, but rather may involve a coordinated response at several levels to permit the efficient expression of specialized differentiated functions.
It has been well established that heterologous antisera against whole rat kidney homogenate when injected into pregnant rats during the embryonic organogenetic period may induce abnormal embryonic development. Attempts were made to isolate the active components from soluble rat kidney extract by ammonium sulfate precipitation, anion-exchange chromatography, and concanavalin A-Sepharose 4B affinity chromatography. The glycoproteins isolated were capable of stimulating the production of potent rabbit antisera. When injected ip into the 9th day pregnant rats, these antisera induced embryonic death, congenital abnormalities, and fetal growth retardation. Eighty-four surviving fetuses were examined, all of them were malformed. The most frequently observed congenital defects were anophthalmia and microphthalmia. Attempts were made to analyze the glycoprotein fraction by discontinuous and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The results indicate that the glycoproteins were of high molecular weight and could be dissociated by SDS into a multitude of molecules or subunits. Although double immunodiffusion indicated that there were one major and two minor antigens in the glycoprotein fraction, attempts to identify the antigens as to their size by analytical gel electrophoresis have not been successful. Electron microscopic study seemed to suggest that the glycoproteins might tend to aggregate to form particulates. The underlying mechanism whereby the antisera to these glycoproteins induce abnormal embryonic development is not understood. The hypotheses to explain the possible sites of teratogenic antibody interaction are discussed.
Epidermal growth factor (EGF) binds to JEG-3 cells, a tissue culture line of human choriocarcinoma. EGF also stimulates secretion of human chorionic gonadotropin (hCG) and to a lesser extent the secretion of free hCG-alpha.
The ability of adrenocorticotrophic hormone (ACTH) to induce lung maturation was evaluated in fetal lambs. One member of 14 twin pairs between 114 and 138 days of gestation was infused intravenously with 0.5 mg ACTH over 5 days. The lungs of treated versus control lambs were judged more mature by morphologic criteria by the use of light and electron microscopy and by biochemical criteria by the use of lamellar-body-rich cell fractions. None of 5 premature lambs treated with ACTH and allowed to breathe showed evidence of hyaline membrane disease, while 3 untreated control lambs showed typical hyaline membranes.
Membrane glycoproteins have been studied in the normal lactating mammary gland and R3230 AC mammary tumor of the rat. Plasma membrane-enriched fractions were obtained from these tissues by discontinuous sucrose gradient centrifugation of a microsomal preparation from the tissue homogenates. The lightest membrane fractions (F-1 and F-2) have the greatest enrichment of plasma membrane markers, with a 14- to 20-fold purification of 5'-nucleotidase and Na+-K+ -adenosine triphosphatase over the homogenate values in both tumor and normal tissues for F-1. Electron microscopy shows smooth membrane vesicles for these fractions. Polypeptide analysis by acrylamide gel electrophoresis shows essentially the same patterns for F-1 and F-2 and only relatively minor differences between membrane components of tumor and normal tissues. Glycoprotein analysis of the polyacrylamide gels by periodate-Schiff staining indicates more dramatic differences. Membrane Fraction F-1 from normal tissue contains two major glycoproteins, GP-II and GP-III, while Fractions F-2 and F-3 contain an additional glycoprotein, GP-I, with a higher apparent molecular weight. In the tumor, the component corresponding to GP-III is decreased or absent and a new component GP-IV is seen at a lower apparent molecular weight.