Xenopus laevis oocyte calmodulin in the process of meiotic maturation.

A Cartaud,R Ozon,M.P Walsh,J Haiech,J.G Demaille

doi:10.1016/s0021-9258(19)70576-6

Abstract

Calcium ions are postulated to be involved in the process of meiotic maturation of amphibian oocytes. Since several of the calcium effects in eukaryotic cells are mediated by calmodulin, the present study was undertaken to assess the presence and level of calmodulin in Xenopus laevis oocytes before and after progesterone treatment. Calmodulin was shown to be present at a concentration of approximately microM in control oocytes cytosol. This level remained stable for 2 h when the maturation promoting factor appeared, and increased to approximately 44 to 59 microM at the time of the germinal vesicle breakdown. Maturation is therefore associated with calmodulin synthesis. Xenopus calmodulin was isolated from oocyte cytosol after heat treatment, anion exchange chromatography, and gel filtration, with a yield of approximately 23%. When compared to mammalian calmodulins, the amphibian protein exhibited the same ultraviolet absorption spectrum, a similar amino acid composition with 1 residue of trimethyllsine, and the same shape conformers in the absence or presence of divalent metals, as shown by different mobilities upon dodecyl sulfate-polyacrylamide gel electrophoresis. The protein migrated faster in the presence than in the absence of Ca2+ ions, Mn2+ and Mg2+ being less effective. It was able to activate calmodulin-deficient myosin light chain kinase. Its high serine content and the tryptic peptide maps obtained after high performance liquid chromatography point, however, to minor differences in the primary structures of mammalian and amphibian calmodulins.

Highlights

Calcium ions are postulated to be involved in the postulated that calcium ions are released under these condiprocess of meiotic maturation of amphibian oocytes. tions from intracellular stores [2]
Since several of the calcium effects in eukaryotic cells cently demonstrated that progesterone induces a rapid inare mediated bycalmodulin, the present study was crease in intracellular free calcium level in Xenopus luevis undertaken to assess thepresence and level of calmod- oocytes and suggested a possible role for calmodulin in the ulin in Xenopus Zaevis oocytes before and afterproges- maturation process
Ca2+fluxes and/orintracellular exchanges are probably involved in the meiotic maturation process

Summary

Xenopus laevis Oocyte Calmodulinin the Processof Meiotic Maturation*

Annie Cartaud andRene Ozon From the Laboratoire dePhysiologie de la Reproduction, Groupe Steroiiz'es, ERA CNRS 694, Universite Pierre et Marie. Terone treatment.Calmodulin was shown to be present Calcium ions will only act through binding to intracellular at a concentration of -34 p~ in control oocytes cytosol. The oocyte cytosol was found to contain high affinity calcium-bindingsites [9].When examinedby radioelectrophoresis [10] in the presence of45CaC12, the cytosoliccalciumbinding activity migrated essentially with the same RF as phibian protein exhibited the same ultraviolet absorp- calmodulii.' These observations prompted, on the one hand, tion spectrum, a similar amino acid composition with the isolation and characterization of X . Protein concentration was involved in the progesterone-induced maturation of amphib- measured by the Coomassie Blue technique [15].Amino acid analyses ian oocytes [1,2,3].

RESULTS

Calmodulin concentration in oocytes during meiotic maturation

Bovine brain"

Findings

DISCUSSION