CHANGES IN THE ACTIVITY AND PROTEIN-LEVELS OF PROTEASOMES DURING OOCYTE MATURATION IN GOLDFISH (CARASSIUS-AURATUS)

Changes in the activity and protein levels of proteasomes were determi ned in goldfish oocytes during meiotic maturation induced in vitro by 17alpha,20beta-dihydroxy-4-pregnen-3-one (17alpha,20beta-DP), a natura lly occurring maturation-inducing hormone in this species. Both the ac tivity and protein levels of proteasome exhibited two peaks during the 17alpha,20beta-DP-induced oocyte maturation with a similar pattern of fluctuation. The first peak (a 2-fold increase) occurred before the m igration of germinal vesicle (GV) (within 1 h after 17alpha,20beta-DP treatment), followed by a gradual decrease towards GV breakdown (GVBD) , reaching the lowest level at 6 h. The second peak occurred immediate ly after GVBD (7 h after the treatment), followed by a sharp decrease at 8 h. The time of the second peak appears to correspond to the time of the first polar body extrusion, a time when maturation-promoting fa ctor (MPF) activity was shown to decrease transiently in goldfish oocy tes during the 17alpha,20beta-DP-induced meiotic maturation. Thus, it is suggested that proteasomes are involved in the decrease in MPF acti vity during the first polar body extrusion.