Calmodulin triggers the resumption of meiosis in amphibian oocytes.

Abstract

The calcium-binding protein, caimodulin, has been purified from Xenopus laevis oocytes. This 18,500-dalton protein, pl 4.3, has two high-affinity calcium-binding sites per mole protein having a dissociation constant of 2 .8 X 10 -6 M .Full-grown Xenopus oocytes, arrested in late G2 of the meiotic cell cycle, resumed meiosis when microinjected with 60-80 ng (3-4 pmol) of calmodulin in the form of a calciumcalmodulin complex . The timing of the meiotic events in these recipient oocytes was the same as that normally induced by progesterone .Xenopus ovarian calmodulin stimulated bovine brain phosphodiesterase (PDE) 3-to 10-fold in a calcium-dependent manner, but it had no apparent effect on ovarian PDE activity . A calcium-calmodulin-dependent protein kinase has been isolated from Xenopus oocytes using a calmodulin-Sepharose 413 affinity column . The possible role for this kinase in regulating the G2-M transition in oocytes has been discussed .Amphibian oocytes, arrested in late prophase of meiosis (G2), resume meiosis in response to progesterone (26,31) . This resumption leads to the dissolution of the nuclear membrane, followed by chromosome condensation and the meiotic divisions up to the second metaphase . Several observations have led to the suggestion that a progesterone-induced increase in intracellular free calcium may be a necessary first step for the resumption of meiosis (1,15,17,30) . Recently, we have demonstrated directly, using the calcium-specific photoprotein aequorin, that progesterone does cause a rapid, but only transient increase in the free calcium level in oocytes (32) . The mechanism by which an increased calcium activity might regulate the G 2 -M transition remains unsolved at this time .Increasing evidence indicates that a calcium-binding protein, designated calmodulin, plays a key role in regulating many calcium-dependent processes . Calmodulin is a highly conserved protein that has been identified in a variety of cell types; we have presented preliminary evidence suggesting that Xenopus oocytes also contain this protein (27) . In the current study, we have more fully characterized oocyte calmodulin with respect to its physical and biological properties . More significantly, we demonstrate that oocyte calmodulin, in the form of a calcium-calmodulin complex, can trigger the resumption of THE JOURNAL OF CELL BIOLOGY " VOLUME 89 JUNE 1981 389-394 ©The Rockefeller University Press -0021-9525/81/06/0389/06 $1 .00 meiosis (oocyte maturation) when injected into full-grown Xenopus oocytes.We have attempted to elucidate the mechanism by which calmodulin induces the resumption of meiosis in oocytes. The results indicate that oocyte calmodulin does*not regulate ovarian phosphodiesterase but may be involved in the activation of oocyte protein kinases . MATERIALS AND METHODS Isolation of Calmodulin from Xenopus Oocytes and Bovine BrainApproximately 75 g (wet wt) of Xenopusovary were processed as described by Dedman et al . (5) for the preparation of rat testis calmodulin, with the following m...

Effects of protein kinase inhibitors on pig oocyte maturation in vitro

“…Therefore it seems that in the mouse the CaM antagonist W7 inhibits oocyte maturation at the G2-to Mphase border and the first cleavage at the G1-to S-phase transition. In murine (Kaplan et al, 1982;Bornslaeger et al, 1984) and Xenopus oocytes (Cartaud et al, 1980;Wasserman and Smith, 1981) as in somatic tissues (Means et al, 1982) (Huchon et al, 1981;Foulkes and Maller, 1982;Rime et al, 1990). In contrast to the findings in the mouse, W7 at concentrations up to 200 fl M had no effect on pig oocyte maturation in vitro (table IV).…”

Role of calmodulin in blastocyst formation in the mouse

“…However, while extracellular calcium appears to be necessary for the induction and continuous maintenance of compaction (Wales, 1970;Whitten, 1971;Ducibella & Anderson, 1975 ;Bilozur & Powers, 1982) (Schultz, Heller & Buklad, 1983). Calmodulin has been implicated in oocyte maturation in non-mammalian species (Meijer & Guerrier, 1981;Wasserman & Smith, 1981;Hollinger & Alvarez, 1982). Of several possibilities, calmodulin-dependent adenylate cyclase does not appear to play any role in the compaction process (Bilozur & Powers, 1982).…”

Evidence for Involvement of Protein Kinase C in Germinal Vesicle Breakdown in Chaetopterus

“…Further support for this conclusion was obtained in studies in which oocytes were simultaneously treated with TPA and the Ca2+ channel blocker, verpamil. Verapamil blocked NSW-induced GVBD, but not TPA-induced GVBD Calmodulin antagonists inhibit GVBD in all species investigated (18,27,(34)(35)(36). However, most CaM antatgonists also inhibit C-kinase activity at similar concentrations, so the conclusion that CaM is involved in GVBD based on the results cited above must be considered tentative (cf.…”