Identification and characterization of maturation-promoting factor from catfish, Clarias batrachus

Maturation-promoting factor (MPF) extracted from maturing oocytes of catfishes (Clarias batrachus and Heteropneustes fossilis) and carp (Labeo rohita) induces 100% germinal vesicle breakdown (GVBD) when microinjected into Clarias immature unstimulated oocytes. The presence of a similar MPF activity has also been demonstrated in the active fractions collected after superose 12. SDS-PAGE analyses of cytosolic extracts (CE) prepared from immature and mature oocytes revealed the presence of 34- and 46 kDa proteins apart from a few others. Antibody against the PSTAIR sequence of p34(cdc2) recognized 32- and 34 kDa proteins of immature as well as mature oocytes while, 46 kDa protein of mature oocytes was recognized by anti-cyclin B1 antibody. Moreover, labelling of [S-35]methionine was observed mainly in the region of 46 kDa protein band indicating de novo synthesis of this particular protein. Anti-cyclin A antibody did not recognize any proteins of immature or mature oocytes. Cyclin B1 was absent in immature oocytes and ovulated eggs. These findings indicate the presence of p34(cdc2) homologs and cyclin B in the MPF of the catfishes and carp oocytes.