Presence of maturation-promoting factor in 17α,20β-dihydroxy-4-pregnen-3-one-induced oocytes of catfish, Clarias batrachus.

Full-grown immature Clarias batrachus oocytes respond in vitro to exogenous 17α,20β-dihydroxy-4-preg-nen-3-one ( 17α,20β-DP) by undergoing germinal vesicle breakdown (GVBD). Cytosolic extract (CE) prepared from 17α,20β-DP-induced oocytes has been shown to produce similar effect when microinjected into unstimulated immature oocytes of the same fish. A dose of ∼ 50 nl is enough to cause 100% GVBD after 4 h. Maturation-promoting factor was investigated from 17α,20β-DP-induced, immature and cycloheximide treated oocytes incubated in presence of [(35)S] methionine. When the proteins were extracted and analyzed on SDS-PAGE, two prominent bands corresponding to molecular weight 34- and 46-kDa were detected in the CE of mature oocytes. However, labelling of [(35)S] methionine was observed mainly in the region of 46 kDa protein band indicating de novo synthesis of this particular protein during l7α,20β-DP-induction. Further, immunoblotting study by using rabbit anti-cyclin B1 antibody has clearly demonstrated that the protein which is newly synthesized is highly homologous to Xenopus cyclin B1 and goldfish cyclin B.