Translational regulation of cyclin B mRNA by 17α,20β-dihydroxy-4-pregnen-3-one (maturation-inducing hormone) during oocyte maturation in a teleost fish, the goldfish (Carassius auratus)

17 alpha,20 beta-Dihydroxy-4-pregnen-3-one (17 alpha,20 beta-DP) was identified as maturation-inducing hormone (MIH) in several teleost fishes. In goldfish (Carassius auratus), 17 alpha,20 beta-DP induces oocyte maturation by stimulating the de novo synthesis of cyclin B, a regulatory subunit of maturation-promoting factor (MPF). In this study, we examined the control mechanisms of 17 alpha,20 beta-DP-induced de novo synthesis of cyclin B protein in oocytes, which is a prerequisite step for MPF activation during oocyte maturation in goldfish. Cycloheximide-treated oocytes failed to undergo meiotic maturation in response to 17 alpha,20 beta-DP; in this group neither cyclin B nor 34-kDa active cdc2 was detectable in oocytes. In contrast, oocytes exposed to actinomycin D plus 17 alpha,20 beta-DP or 17 alpha,20 beta-DP underwent maturation; in these groups both cyclin B and 34-kDa cdc were present. Northern blotting showed that cyclin B mRNA is present in both immature and mature oocytes.-Sequence analysis revealed that goldfish cyclin B mRNA contains four copies of cytoplasmic polyadenylation element (CPE)-like motifs in the 3' noncoding region, suggesting that the initiation-of cyclin B synthesis during oocyte maturation may be controlled by the elongation of poly (A) tail. We then examined the polyadenylation state of cyclin B mRNA during 17 alpha,20 beta-DP-induced oocyte maturation by means of a PCR poly (A) test, and found that cyclin B mRNA is polyadenylated during oocyte maturation. Polyadenylation of cyclin B mRNA occurred at the same time of germinal vesicle breakdown. Furthermore, cordycepin, an inhibitor of poly (A) addition of mRNA, prevented 17 alpha,20 beta-DP-induced oocyte maturation. These findings suggest that,in goldfish oocytes, the synthesis of cyclin B protein is under translational control and that cytoplasmic 3' poly(A) elongation is involved in 17 alpha,20 beta-DP-induced translation of cyclin B mRNA. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.