Hormonal regulation of RNA synthesis and specific gene expression in Xenopus oviduct cells in primary culture

The studies described in this report were carried out as a first step towards the elucidation of mechanisms underlying the tissue specificity of regulation of gene expression by estrogen. Using a procedure established earlier in our laboratory for primary culture of Xenopus hepatocytes, we have characterized how estradiol-17 beta and progesterone affect the rate of synthesis of total RNA and that of accumulation of two oviduct-specific mRNAs in Xenopus oviduct cells in primary culture. In cells that had recovered from 'culture shock' 3 days after they were plated out, both hormones had only a slight or no effect on the overall rate of labelling of newly synthesized RNA over 24 h. Cloned cDNA probes for two mRNAs, termed 7F and 6G and specifying as yet unknown proteins expressed in the oviduct and not in the liver, were used to quantify the two mRNAs. The levels of both mRNAs declined for the first 2 days in culture after which they were stabilized. When added to the oviduct cell cultures 3 days after they were plated out, estradiol increased the steady-state concentration (relative to total RNA) of 7F and 6G mRNAs by 3- to 7-fold after 60-80 h, but with different time-course and dose-response kinetics for the two messages. The antiestrogen tamoxifen also exerted different degrees of antagonist effect on the estrogen-induced accumulation of 7F and 6G mRNAs. Although the protein products of these two oviduct-specific mRNAs have not yet been characterized, these studies set the stage for comparing the regulation by estrogen of their genes with that of vitellogenin genes in primary cultures of Xenopus oviduct cells and hepatocytes.