Direct induction of vitellogenin production in cultured male amphibian hepatocytes by estradiol-17 beta has been accomplished. Liver cells were isolated from adult male bullfrogs by collagenase perfusion and maintained as monolayers in serum-free medium containing insulin and estradiol. Vitellogenin production was measured by direct immunoprecipitation from radioactively labeled secreted protein with a specific antiserum against vitellogenin. Significant quantities of vitellogenin were detected in the exported protein on the second day of hormone treatment. Vitellogenin production increased with duration of culture in the presence of estradiol until by the eighth day approximately 90% of secreted protein was vitellogenin. This response is largely comparable to that obtainable in vivo. Indirect immunofluorescence microscopy was used to identify cells synthesizing vitellogenin in response to estradiol. An increase in cytoplasmic fluorescence could be seen in cells throughout the cultures, with increasing time in the presence of estradiol. By the sixth day of treatment, the majority of cells showed significant fluorescence labeling. The results suggest that studies on the mechanisms underlying the primary activation of the vitellogenin gene may now be conducted under well defined conditions in a monolayer liver cell culture system.

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