Cyclin B in fish oocytes: Its cDNA and amino acid sequences, appearance during maturation, and induction of p34cdc2 activation

Authors:
Publisher website
Google Scholar
Abstract
Under the influence of maturation‐inducing hormone (MIH) secreted from follicle cells, oocyte maturation is finally triggered by maturation‐promoting factor (MPF), which consists of a homolog of the cdc2+ gene product of fission yeast (p34cdc2) and cyclin B. Two species of cyclin B clones were isolated from a cDNA library constructed from mature goldfish oocytes. Sequence comparisons revealed that these two clones are highly homologous (95%) and were found to be similar to Xenopus cyclin B1. Using monocional antibodies against Escherichia coli produced goldfish cyclin B and the PSTAIR sequence of p34cdc2, we examined the levels of cyclin B and p34cdc2 proteins during goldfish oocyte maturation induced in vitro by 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (17α,20β‐DP), a natural MIH in fish. Protein p34cdc2 was found in immature oocyte extracts and did not remarkably change during oocyte maturation. Cyclin B was not detected in immature oocyte extracts and appeared when oocytes underwent germinal vesicle breakdown. Cyclin B that appeared during oocyte maturation was labelled with [35S]methionine, indicating its de novo synthesis. Introduction of E. coli‐produced cyclin B into immature oocyte extracts induced p34cdc2 (MPF) activation. Although the possibility that immature goldfish oocytes contain an insoluble cyclin B is not completely excluded, these results strongly suggest that 17α, 20β‐DP induced oocytes to synthesize cyclin B, which in turn activates preexisting p34cdc2, forming active MPF.

This publication has 47 references indexed in Scilit: