Calmodulin-dependent protein kinase II mediates inactivation of MPF and CSF upon fertilization of Xenopus eggs

Abstract

In vertebrates, unfertilized eggs are arrested at second meiotic metaphase by a cytostatic factor (CSF), an essential component of which is the product of the c-mos proto-oncogene. CSF prevents ubiquitin-dependent degradation of mitotic cyclins and thus inactivation or the M phase-promoting factor (MPF). Fertilization or parthenogenetic activation triggers a transient increase in the cytoplasmic free Ca2+ (reviewed in refs 5 and 6), inactivates both CSF and MPF, and releases eggs from meiotic metaphase arrest. A calmodulin-dependent process is required for cyclin degradation to occur in cell-free extracts prepared from metaphase II-arrested eggs (CSF extracts) when the free Ca2+ concentration is transiently raised in the physiological micromolar range. Here we show that when a constitutively active mutant of calmodulin-dependent protein kinase II (CaM KII) is added to a CSF extract, cyclin degradation and Cdc2 kinase inactivation occur even in the absence of Ca2+, and the extract loses its ability to cause metaphase arrest when transferred into embryos. Furthermore, specific inhibitors of CaM KII prevent cyclin degradation after calcium addition. Finally, the direct microinjection of constitutively active CaM KII into unfertilized eggs inactivates Cdc2 kinase and CSF, even in the absence of a Ca2+ transient. The target for Ca(2+)-calmodulin is thus CaM KII.

An ATM- and ATR-dependent checkpoint inactivates spindle assembly by targeting CEP63

“…Or alternatively, CSF arrest can be determined through the detection of Cyclin B (data not shown). The presence of low calcium concentration activates Cyclin B destruction driving mitosis exit Kobayashi et al, 1992;Lorca et al, 1993). It is worth reiterating at this point that CSF arrested extracts are meiotic (meiosis II), but enable relevant insights by mimicking mitosis.…”

Cdc2 and Mos Regulate Emi2 Stability to Promote the Meiosis I–Meiosis II Transition

“…In addition to playing a role in MI, Mos kinase is a critical component of cytostatic factor (CSF), an activity required for arrest in MII (Masui and Markert, 1971;Lorca et al, 1993). Although Mos has been long known to act as a constituent of CSF (through activation of the MAPK pathway, as in MI; Sagata et al, 1989;Haccard et al, 1993), its precise mechanism of action was not clear.…”

Ca2+ signaling differentiation during oocyte maturation

“…The fertilization-induced Ca 2þ signal also mediates the completion of meiosis II with the extrusion of the second polar body and entry into mitosis, through Ca 2þ -calmodulin dependent protein kinase II (CaMKII) activation (Lorca et al, 1993). CaMKII mediates the meiotic to mitotic transition by inactivating both maturation promoting factor (MPF) and cytostatic factor (CSF; Lorca et al, 1993;Morin et al, 1994;Knott et al, 2006).…”

“…CaMKII mediates the meiotic to mitotic transition by inactivating both maturation promoting factor (MPF) and cytostatic factor (CSF; Lorca et al, 1993;Morin et al, 1994;Knott et al, 2006). CaMKII mediates this effect by phosphorylating the APC inhibitor XErp1/Emi2 (Liu and Maller, 2005;Rauh et al, 2005;Hansen et al, 2006).…”