Effect of estradiol and progesterone on c-myc expression in the sea star testis and the seasonal regulation of spermatogenesis.
Analysis of the expression of cell cycle control genes provides a sensitive assay for mitotic and meiotic progression under experimental conditions. Transcription of the c-myc proto-oncogene and thymidine incorporation into DNA were both used to assay the mitogenic effects of estradiol and progesterone on the testicular germinal epithelium of the starfish Asterias vulgaris. Experimental in vitro studies during the annual spermatogenic cycle show that testes are not sensitive to mitotic stimulation by estradiol alone, whereas progesterone alone is mitotically inhibitory. The germinal epithelium can only be mitotically stimulated by estradiol after pretreatment with progesterone. The net increase in mitotic activity following a progesterone to estradiol transfer is dependent on the length of progesterone pretreatment. Overall, the seasonal pattern of testicular estradiol and progesterone levels evident in field populations of A. vulgaris (Hines et al., 1992a: Endocrinology 100:1468-1471) do not appear to be responsible for initiating spermatogonial mitosis at the onset of the annual spermatogenic cycle. Expression rates of the c-myc proto-oncogene are substantially more sensitive than thymidine incorporation in quantifying mitotic activity. Measuring proto-oncogene expression provides an ideal experimental approach to investigations of the regulatory mechanisms that control growth and reproduction in marine organisms.
Marsh
A G
AG
Department of Zoology, University of New Hampshire, Durham 03824.
Walker
C W
CW
D000818:Animals; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D004958:Estradiol / Q000494:pharmacology*; D016259:Genes, myc / Q000187:drug effects*; D008297:Male; D011374:Progesterone / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012621:Seasons; D013091:Spermatogenesis / Q000187:drug effects* / Q000235:genetics* / Q000502:physiology; D013215:Starfish / Q000187:drug effects / Q000235:genetics*; D013737:Testis / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism
D012333:RNA, Messenger; D011374:Progesterone; D004958:Estradiol; D004247:DNA; D013936:Thymidine