title: Gamma-ray exposure accelerates spermatogenesis of medaka fish, Oryzias latipes.
abstract: To examine the spermatogenesis (and spermiogenesis) cell population kinetics after gamma-irradiation, the frequency and fate of BrdU-labeled pre-meiotic spermatogenic cells (spermatogonia and pre-leptotene spermatocytes) and spermatogonial stem cells (SSCs) of the medaka fish (Oryzias latipes) were examined immunohistochemically and by BrdU-labeling. After 4.75 Gy of gamma-irradiation, a statistically significant decrease in the frequency of BrdU-labeled cells was detected in the SSCs, but not in pre-meiotic spermatogenic cells. The time necessary for differentiation of surviving pre-meiotic spermatogenic cells without delay of germ cell development was shortened. More than 90% of surviving pre-meiotic spermatogenic cells differentiated into haploid cells within 5 days after irradiation, followed by a temporal spermatozoa exhaust in the testis. Next, spermatogenesis began in the surviving SSCs. However, the outcome was abnormal spermatozoa, indicating that accelerated maturation process led to morphological abnormalities. Moreover, 35% of the morphologically normal spermatozoa were dead at day 6. Based on these results, we suggest a reset system; after irradiation most surviving spermatogenic cells, except for the SSCs, are prematurely eliminated from the testis by spermatogenesis (and spermiogenesis) acceleration, and subsequent spermatogenesis begins with the surviving SSCs, a possible safeguard against male germ cell mutagenesis.
authors.affiliation: Laboratory of Radiation Biology, Department of Biological Sciences, Graduate School of Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Tokyo 277-8562, Japan. ss07191@mail.ecc.u-tokyo.ac.jp
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Kuwahara
authors.forename: Atsuko
authors.initials: A
authors.lastname: Shimada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mitani
authors.forename: Akihiro
authors.initials: A
authors.lastname: Shima
mesh_terms: D000818:Animals; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D008297:Male; D009990:Oryzias / Q000502:physiology*; D013091:Spermatogenesis / Q000528:radiation effects*; D013737:Testis / Q000528:radiation effects