TRANSLATIONAL REGULATION OF THE GRADUAL INCREASE IN HISTONE H1 KINASE-ACTIVITY IN MATURING MOUSE OOCYTES

In maturing mouse oocytes, p34(cdc2)-associated histone H1 kinase acti vity gradually increases until it reaches its maximum at metaphase I ( Choi et al., 1991: Development 113:789-795). In this study, treatment of oocytes with cycloheximide resulted in a failure to increase the le vel of histone H1 activity above that detected at approximately the ti me of germinal vesicle breakdown (GVB), which is similar to 20-30% of the level normally achieved at metaphase I. Cyclin B was detected in G V-stage oocytes, but there was a 2-2.5-fold increase in the amount of cyclin B in maturing oocytes from GV-stage to metaphase I and a burst of cyclin B synthesis during the first 3 hr of maturation. Okadaic aci d-treatment of mouse oocytes did not accelerate activation of histone H1 kinase but rather arrested its activity at the same level observed in cycloheximide-treated oocytes. Thus the components of the p34(cdc2) kinase activating system in mouse oocytes are apparently not present in GV-stage oocytes in an amount or configuration that would allow max imum kinase activation when meiosis is reinitiated by okadaic acid. Im portantly, okadaic acid-treatment dramatically inhibited protein synth esis. Therefore, the inhibition of protein synthesis by okadaic acid p robably abrogates the possibility of de novo synthesis of the regulato rs of p34(cdc2) kinase required to drive its activity to the maximum l evel normally achieved by metaphase I. It is concluded that there is a critical point in driving the continued activation of histone H1 kina se that occurs at approximately the time of GVB. Progression beyond th is point requires de novo protein synthesis. Since newly synthesized c yclin B is immediately complexed with the p34(cdc2) kinase in maturing mouse oocytes, cyclin B is a candidate for one of the proteins whose synthesis is required to drive the continued increase in histone H1 ki nase activity after the time of GVB. (C) 1995 Wiley-Liss, Inc.