Coordinate and Non‐coordinate Estrogen‐Induced Expression of A and B Groups of Vitellogenin Genes in Male and Female Xenopus Hepatocytes in Culture

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Abstract
The concentration of mRNA transcribed from A and B groups of vitellogenin genes, induced by estrogen added to primary cultures of hepatocytes from male and female adult Xenopus, was measured by a technique of filter disc hybridization with cloned Xenopus vitellogenin cDNA probes. In cells from naive male Xenopus (i.e. not previously exposed to hormone in vivo or in vitro), the two groups of the multigene family were non‐coordinately expressed during the early stages of response to estradiol in vitro. Only B group transcripts could be detected for the first 2–3 h. At later times, or upon successive additions of estradiol to the male cell cultures, both A and B group mRNAs accumulated at the same rate and to the same extent. In female hepatocytes both groups of mRNAs accumulated in parallel at all stages of their response to estrogen, reaching levels 10‐fold higher than in naive male cells similarly exposed to the hormone. However, hepatocytes from male Xenopus that had received a single injection of estradiol 5 weeks before the cells were prepared, now exhibited identical rates and extent of accumulation of A and B groups of vitellogenin mRNAs to those observed in female cells. Pulse‐labeling of RNA in cultured male Xenopus hepatocytes confirmed that the coordinate and non‐coordinate accumulation of mRNAs were largely a function of differential or equal transcription of the A and B groups of vitellogenin genes. A phenomenon analogous to the hormone‐induced shift from non‐coordinate to coordinate expression of two groups of genes of the same multigene family has not been described previously, and we discuss possible mechanisms underlying the transition.