DIFFERENTIAL EFFECT OF ACTIVATORS OF PROTEIN-KINASE-C ON CYTOSKELETALCHANGES IN MOUSE AND HAMSTER EGGS

Treatment of metaphase II-arrested hamster eggs with activators of pro tein kinase C has been reported to promote resumption of the cell cycl e, second polar body emission, and pronucleus formation (G. I. Gallica no, S. M. Schwarz, R. W. McGaughey, and D. G. Capco, 1993, Dev. Biol. 156, 94-106). In contrast, we have not observed these responses in mou se eggs obtained from CF-1 mice treated with these activators. In this report, we evaluated if this difference was due to differences in the technique used for PKC stimulation in the two different laboratories or due to species differences. Metaphase II-arrested hamster or mouse eggs were treated with phorbol diesters for 5 min or with a membrane-p ermeable diacylglycerol for 1 hr. Treatment of hamster eggs resulted i n (1) the formation of ''second polar body-like structures'' commencin g 5 min after treatment and reaching a maximum by 20-40 min; (2) a rem arkable increase in the staining of filamentous actin in the region of these polar body-like structures; and (3) the disassembly of spindle microtubules. A reduction in cdc2/cyclin B1 kinase activity, as assess ed by a decrease in H1 kinase activity, as well as progression from me taphase to anaphase were not observed. Treatment of mouse eggs from ei ther CF-1 or CD-1 mice with these activators of PKC did not result in the formation of these polar body-like structures, did not cause an in crease in filamentous actin, and did not result in a reduction in hist one H1 kinase activity. This treatment, however, did induce disassembl y of the spindle microtubules and the formation of multiple ''pronucle us-like structures'' that were more discernible in eggs from CD-1 mice . We conclude that the ''apparent'' activation of hamster eggs by acti vators of PKC is due to the effect of these agents on the cytoskeleton , which gives rise to structures that appear similar to polar bodies, but without any evidence of cell cycle resumption. The different respo nses seen in mouse and hamster eggs are mainly due to differences in t he sensitivity of the cytoskeleton to rearrangements induced by these agents. (C) 1995 Academic Press, Inc.