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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

Estrogen regulation of the biological activity of the avian oviduct progesterone receptor and its ability to induce avidin.

During primary estrogen stimulation of chick oviduct development, estrogen withdrawal, or secondary estrogen treatment, changes in the oviduct progesterone receptor ( PR) occur. The presence of estrogen appears to regulate not only PR concentration but also its biochemical activity, i.e. its capacity to bind to nuclear acceptor sites and alter RNA synthesis. This study reports that estrogen regulates the nuclear binding capacity of the PR even more rapidly than previously reported in fully developed oviducts of chicks that have been injected daily for 4 weeks with diethylstilbestrol (DES). Further, the nuclear binding capacity of the PR correlates with the ability of progesterone (P) to induce avidin protein concentrations in the oviducts in vivo. The PR concentration in the oviducts increases 2-fold within 8 h of the last injection and the decreases to a minimal value by 24 h. Injection of [3H]P into the chicks shows that the in vivo nuclear localization of the steroid increases almost 4-fold at 8 h, followed by a similar decrease to minimal values by 24 h. Cell-free nuclear binding assays, using PR isolated at various times after the last DES injection and oviduct nucleoprotein complexes, indicate that the capacity of the receptors to bind to nuclear acceptor sites is regulated by the estrogen. The enhanced nuclear binding capacity of the isolated PR increases to maximal values by 12-14 h after the last estrogen treatment and then begins to decrease to minimal values by 24 h. Similarly, the ability of P to induce in vivo avidin protein concentrations and to alter general RNA synthesis in the oviducts is reduced by 70% (of the estrogen non-withdrawn chick levels) by 24 h after the last estrogen injection. These changes over the 24-h period after the last DES treatment are not due to changes in the serum DES concentrations. The following 10-day period of estrogen withdrawal reveals a cyclic decaying pattern in the capacity of the PR for nuclear binding. The P induction of avidin and alteration of RNA polymerase II activity, using nuclear run-off experiments, also show a similar cyclic decaying pattern. By 6 days of estrogen withdrawal, the PR is incapable of any nuclear binding, and P cannot induce avidin protein concentrations in the oviducts. Serum DES concentrations over this 10-day period display only a gradual decay.(ABSTRACT TRUNCATED AT 400 WORDS)[1]


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