Regulation of Protein Synthesis in Chick Oviduct: IV. ROLE OF TESTOSTERONE

Abstract

Abstract Dihydrotestosterone acts synergistically with estrogen to stimulate the growth of the magnum portion of the chick oviduct which synthesizes the egg white proteins, but it is inactive when administered alone. The stimulation of growth is attributable to an increased number of magnum cells and an increased rate of protein synthesis per cell. The mechanisms by which protein synthesis could be enhanced were investigated. There was no significant change in the rate of polypeptide elongation or initiation when dihydrotestosterone was administered along with estrogen. There was, however, an increase in the amount of ribosomes and messenger RNA per cell; an increase in ovalbumin mRNA per cell was shown directly using a cell-free protein-synthesizing system. The relative rates of synthesis of ovalbumin, conalbumin, and lysozyme were similar after treatment with either estrogen and dihydrotestosterone or estrogen alone, suggesting that the concentrations of these mRNAs were increased proportionately; however, there was a 2-fold increase in the relative rate of ovomucoid synthesis. Dihydrotestosterone did not affect the rate of ovalbumin or ovomucoid mRNA degradation. Thus, we conclude that dihydrotestosterone stimulates some aspect of mRNA transcription, maturation, or transport to the cytoplasm. Ribosomal RNA synthesis was shown to be enhanced by dihydrotestosterone as well. Nuclei isolated from the magnum of chicks treated with estrogen and dihydrotestosterone had a higher rate of RNA synthesis than those from chicks treated with estrogen alone. The activity of both the A and B forms of RNA polymerase was enhanced, and this was not due to differential RNase activity or differences in nucleotide pool sizes. The rate of RNA chain elongation was found to be similar in both nuclear preparations, and there was negligible initiation of RNA chains in either preparation as judged by the use of rifampicin AF/013. Thus, the different RNA polymerase activities probably reflect the number of transcribing polymerase molecules. Dihydrotestosterone did not affect the total extractable RNA polymerase activity (Form A or B), suggesting that this enzyme is not rate-limiting. We conclude that dihydrotestosterone probably stimulates the rate of RNA polymerase initiation on genes activated by estrogen.