Steroid- induced meiosis in Rhinella arenarum oocytes: MPF activation?.

ARIAS TORRES, AJ; BUHLER, MI; ZELARAYÁN, LI

Tucumán

Jornada; XXXI Jornadas Científicas Asociación de Biología de Tucumán; 2014

Asociación de Biología de Tucumán

STEROID-INDUCED MEIOSIS IN Rhinella arenarum OOCYTES: MPF ACTIVATION   Arias Torres A.J, Bühler M.I,  Zelarayán, L.I.   Instituto Superior de Investigaciones Biológicas (INSIBIO), CONICET-UNT, Inst. de Biología, Fac. de Bqca., Qca. y Fcia, UNT. Tucumán.  anajoarias@hotmail.com   There is controversy about the role of steroids in amphibian oocyte maturation and no direct evidence exists of progesterone (P4) being the natural inducer steroid. However, androgens may induce oocyte maturation in other taxa. The oocyte maturation is regulated by Maturation Promoting Factor (MPF). The pre-MPF activation depends on its dephosphorylation by cdc25 phosphatase that catalyzes its conversion to active MPF. This paper analyzes the effect of various steroids on in vitro maturation of R. arenarum oocytes and the participation of MPF in this process. Mature females of R. arenarum harvested over all the year in Tucumán. Dose (10-9-10-5 M) and time response curves with 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 steroids induced oocyte maturation was analyzed by inhibition of the cdc25 phosphatase with NaVO3 (0.1-1.0 mM) and through cytoplasmic microinjection experiments. The results indicate that the tested steroids induce follicle and oocyte GVBD in a dose and time dependent. During the breeding season P4 and P5 were the most effective drugs (EC50 = 7 and 25 nM respectively). During the non-reproductive period oocyte response to all steroids was markedly lower. While the response to androgens was variable in no case exceeded induced P4. Inactivation of cdc25 with NaVO3 inhibited GVBD induced by steroids in a dose dependent manner. Microinjection of cytoplasm matured with DHEA, AD or T induced maturation of immature oocytes. In R. arenarum oocytes the androgens may induce resumption of meiosis and can activate the MPF. Nevertheless P4 sensitivity is higher, especially during the breeding season.