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

beta-adrenoceptor antagonists reinitiate meiotic maturation in Clarias batrachus oocytes

Effects of beta-adrenoceptor antagonists propranolol and alprenolol in the oocyte maturation of the catfish (Clarias batrachus) were investigated under in vitro. Cyclic AMP (cAMP) levels were also measured in the control, propranolol and phosphodiesterase (PDE) inhibitor treated oocytes. When full-grown folliculated oocytes were cultured in vitro in the presence of different concentrations of propranolol or alprenolol, both the substances induced germinal vesicle breakdown (GVBD) in a dose-dependent manner. The maturational effect of alprenolol at the concentration of 1.0 mM was similar to that of the 1.5 mM dose of propranolol inducing more than 88% GVBD. In the time course study, when the oocytes were treated with 1.5 mM propranolol or with 1.0 mM alprenolol for various times, both the antagonists induced more than 80% GVBD after 4 h of incubations and this induction gradually increased with the increased duration of treatments. On the other hand, 1.5 mM propranolol treatment caused a significant decrease in oocyte cAMP which was maintained upto the duration of the study (36 h). When the oocytes were first stimulated by 1.5 mM propranolol or 1.0 mM alprenolol for 4 h and then treated with various doses of cAMP or PDE inhibitors (IBMX and theophylline), all these substances effectively blocked beta-adrenoceptor antagonist-induced GVBD. Both these PDE inhibitors promoted the accumulation of cAMP in the oocytes. These results provide the first example of an existence of a cAMP-mediated mechanism of action of beta-adrenoceptor antagonists in the induction of oocyte maturation in fish.

Partial purification of maturation-promoting factor from catfish, Clarias batrachus: identification as the histone H1 kinase and its periodic activation

Maturation-promoting factor (MPF) has been demonstrated in the 100,000 g supernatant of 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha, 20 beta-DP)-induced catfish, Clarias batrachus oocytes using DEAE-cellulose and sephadex G-200 chromatography. Partially purified MPF molecule eluted as a single peak on sephadex G-200 with molecular mass of approximately 200 kDa in native PAGE. SDS-PAGE analysis showed the presence of five proteins of 32, 34, 45, 46 and 48 kDa. Antibody against the PSTAIR sequence of p34cdc2 recognized 32 and 34 kDa proteins, whereas rabbit anti-cyclin B1 and B2 crossreacted with 46 and 48 kDa proteins, respectively. Cyclin B was absent in immature oocytes and appeared after 7 h of 17 alpha, 20 beta-DP stimulation, coinciding with the histone H1 kinase (HH1K) activity and start of germinal vesicle breakdown (GVBD). Our data indicate that C. batrachus MPF is a complex of cdc2 kinase and cyclin B molecules. A close relationship between HH1K activity and catfish oocyte maturation has been demonstrated using cycloheximide, cytochalasin B and colchicine. HH1K activation was inhibited by cycloheximide, while cytochalasin B and colchicine were ineffective. These finding suggests that the activation of HH1K depends on protein synthesis, whereas disruption of microfilaments influences only nucleus migration without effect on GVBD or HH1K activation. An increase of phosphorylated proteins after activation of catfish oocytes with 17 alpha, 20 beta-DP has also been observed.