Activation of maturation promoting factor and 26S proteasome assembly accelerated by a high concentration of 1-methyladenine in starfish oocytes

In the oocyte maturation process of the starfish Asterina pectinifera, the extent of inhibition of germinal vesicle breakdown (GVBD) by the proteasome inhibitor MG115 (benzyloxycarbonyl-leucyl-leucyl-norvalinal), as well as t he timing of activation of pre-MPF (inactive maturation promoting factor) a nd 26S proteasome assembly, were found to be dependent on the concentration of the maturation-inducing hormone 1-methyladenine (1-MeAde). Activation o f pre-MPF was accelerated by increasing the concentration of 1-MeAde, while there was little effect on the time required far GVBD, Assembly of the 26S proteasome was also accelerated by increasing the concentration of 1-MeAde . These results indicate that a higher concentration of 1-MeAde triggers ac celeration of the assembly and increase in the activity of the 26S proteaso me, which results in activation of pre-MPF, although there is little effect on the timing of GVBD. It was also clarified that the timing of GVBD is co ntrolled by a rate-liming step after MPF-activation.