Enhanced c-myc transcript abundance has been observed in a variety of human malignancies, in normal liver tissue induced to proliferate in vivo by partial hepatectomy and in cells in culture induced to proliferate with the addition of protein hormones and growth factors. Little is known, however, about the expression of cellular proto-oncogenes in cells induced to proliferate in vivo by steroid hormones. Experiments reported here indicate that when cells of the immature chicken oviduct are induced to undergo rapid in vivo proliferation by application of the estrogen hormone 17 beta-estradiol, the onset of this proliferation is associated with a rapid, large, and transient increase in c-myc transcript abundance. When estrogen is administered to chickens in which the oviduct has already differentiated, neither massive cell proliferation nor large increases in c-myc transcript abundance are induced. We conclude that the abundance of c-myc transcripts in vivo correlates well with the degree of cell proliferation induced by steroid hormone.

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