Calcium/calmodulin-dependent protein kinase II and calmodulin: Regulators of the meiotic spindle in mouse eggs

Elevation of intracellular free calcium causes egg activation by initiating a cascade of interacting signaling pathways that, in unison, act to remode l the cytoplasmic compartment and the nuclear compartment of the egg. We sh ow here that calcium/calmodulin-dependent protein kinase II (CaM kinase II) is tightly associated with the meiotic spindle and that 5 min after egg ac tivation there is a transient, tight association of calmodulin (colocalized with CaM kinase II) on the meiotic spindle. These correlative observations caused us to test whether activation of CaM kinase II mediated the chromos omal transit into an anaphase configuration. We demonstrate that calcium an d calmodulin, at physiological levels, along with ATP were capable of drivi ng the spindle (with its associated CaM kinase II) into an anaphase configu ration in a permeabilized egg system. The transit into anaphase was depende nt on the presence of both calcium and calmodulin and occurred normally whe n they were present at a ratio of 4 to 1. Peptide and pharmacologic inhibit ors of CaM kinase II blocked the transit into anaphase, both in the permeab ilized egg system and in living eggs (inhibitors of protein kinase C did no t block the transit into anaphase). Using a biochemical approach we confirm that CaM kinase II increases in activity 5 min after egg activation and th at a second increase occurs 45 min after activation at the approximate time that the contractile ring of the second polar body is constricting. This c orresponds to the approximate time when calmodulin and CaM kinase II coloca lize at several points in the activated egg including the region containing midzone microtubules. CaM kinase II appears localized on midzone microtubu les as soon as they form and may have a role in specifying the position of the contractile ring of the second polar body. (C) 1998 Academic Press.