Effects of actinomycin D and cycloheximide on gonadotropin- or 17α., 20β-dihydroxy-4- pregnen-3-one-induced in vitro maturation in oocytes of the catfish, Clarias batrachus.

ABSTRACT

The effect of inhibitors in the oocyte maturation of Clarias batrachus, was investigated in vitro using actinomycin D and cycloheximide. Full-grown immature oocytes incubated with salmon gonadotropin (SG-G100) and 17α, 20ß-dihydroxy-4-pregnen-3-one at the concentration of 1 μg/ml induced 86·0 ± 1·2% and 91·3 ± 2·4% of germinal vesicle breakdown, respectively. When the oocytes were incubated with SG-G100 (1 μg/ml) + different concentrations of actinomycin D or cycloheximide, a significant drop in the frequency of germinal vesicle breakdown was observed. Thus, gonadotropin-induced maturation was inhibited by both transcriptional and translational inhibitors. When the oocytes were incubated with 17α, 20ß-dihydroxy-4-pregnen-3-one (1μg/ml) + different concentrations of cycloheximide, a significant inhibition of germinal vesicle breakdown was recorded. However, the maturation was not inhibited when the oocytes were incubated in the presence of 17α, 20ß-dihydroxy-4-pregnen-3-one (1 μg/ml) and different concentrations of actinomycin D. This suggests that mRNA synthesis is not obligatory for 17α, 20β- dihydroxy-4-pregnen-3-one induced oocyte maturation. Based on the time course experiment, it was observed that the inhibition of maturation in cycloheximide treated oocytes extends up to 12 h after which the effect becomes slowly subdued.