CONICET | Buscador de Institutos y Recursos Humanos

STEROID-INDUCED MEIOSIS IN Rhinella arenarum OOCYTES:MPF ACTIVATION AriasTorres AJ; Bühler MI; Zelarayán LI. Instituto Superior de InvestigacionesBiológicas (INSIBIO), CONICET-UNT, Inst. de Biología, Fac. de Bqca., Qca. yFcia, UNT. Tucumán. E-mail:anajoarias@hotmail.com There is controversy about the role of steroids inamphibian oocyte maturation and no direct evidence exists of progesterone (P4)being the natural inducer-steroid. However, androgens may induce oocytematuration in other taxa. The oocyte maturation is regulated by Maturation PromotingFactor (MPF). The pre-MPF activation depends on its dephosphorylation by cdc25phosphatase that catalyzes its conversion to active MPF. This work analyzes theeffect of various steroids on in vitro maturation of R. arenarum oocytesand the participation of MPF in this process. Mature females of R. arenarum harvestedthroughout the year in Tucumán. Dose (10-9-10-5 M) and time response curveswith oocytes or follicles in the presence of different steroids (P4, T =testosterone, DHEA = dehidroepiandrostenodione, AD = androstenedione, and P5 =pregnenolone) were performed. The MPF participation on steroid-induced oocytematuration was analyzed by inhibition of the cdc25 phosphatase with NaVO3 (0.1-1.0mM) and through cytoplasmic microinjection experiments. The results indicate that the tested steroids inducefollicle and oocyte GVBD in a dose and time dependent manner. During thebreeding season P4 and P5 were the most effective drugs (EC50 = 7 and 25 nMrespectively). During the non-reproductive period oocyte response to allsteroids was markedly lower. While the response to androgens was variable in nocase did it exceed that induced by P4. Inactivation of cdc25 with NaVO3 inhibitedGVBD induced by steroids in a dose-dependent manner. Microinjection ofcytoplasm matured with DHEA, AD or T induced maturation of inmature oocytes.In R. arenarum oocytes the androgens may induceresumption of meiosis and can activate the MPF. Nevertheless P4 sensitivity ishigher, especially during the breeding season.