Isolation of differentially expressed mRNA in ovaries after estrogen withdrawal in hypophysectomized diethylstilbestrol-treated rats: increased expression during apoptosis.

Ovarian follicular atresia occurs throughout follicular development and involves apoptosis. In addition to regulation by various hormones and growth factors, ovarian granulosa cell apoptosis was shown to be dependent on transcription and translation since the spontaneous onset of DNA degradation in incubated rat granulosa cells was inhibited by actinomycin-D or cycloheximide. Using differential display of mRNA, five transcriptionally upregulated cDNA clones were isolated in the ovary after withdrawal of the anti-apoptotic factor, estrogen. Two of these estrogen-regulated genes, designated ARG-33 and ARG-40, were further characterized using Northern blot hybridizations. ARG-40 showed increased mRNA expression during apoptosis after estrogen withdrawal in the ovary, and after androgen withdrawal in the prostate, while ARG-33 was upregulated during apoptosis only after estrogen withdrawal. This suggests that the two cDNA clones are regulated by steroids, and may be involved in apoptosis in these tissues. ARG-40 showed high homology to cytochrome b, while ARG-33 was novel.