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Ca²⁺ Homeostasis Regulates Xenopus Oocyte Maturation¹

Departments of Physiology & Biophysics,³ Neurobiology & Developmental Sciences,⁴ Geriatrics⁵ and Immunology & Microbiology,⁶ and the Arkansas Cancer Research Center,⁷ University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205 CNRS UMR6061,⁸ Genetique et Developpement, Universite de Rennes 1, 35043 Rennes, France

ABSTRACT

In contrast to the well-defined role of Ca²⁺ signals during mitosis, the contribution of Ca²⁺ signaling to meiosis progression is controversial, despite several decades of investigating the role of Ca²⁺ and its effectors in vertebrate oocyte maturation. We have previously shown that during Xenopus oocyte maturation, Ca²⁺ signals are dispensable for entry into meiosis and for germinal vesicle breakdown. However, normal Ca²⁺ homeostasis is essential for completion of meiosis I and extrusion of the first polar body. In this study, we test the contribution of several downstream effectors in mediating the Ca²⁺ effects during oocyte maturation. We show that calmodulin and calcium-calmodulin-dependent protein kinase II (CAMK2) are not critical downstream Ca²⁺ effectors during meiotic maturation. In contrast, accumulation of Aurora kinase A (AURKA) protein is disrupted in cells deprived of Ca²⁺ signals. Since AURKA is required for bipolar spindle formation, failure to accumulate AURKA may contribute to the defective spindle phenotype following Ca²⁺ deprivation. These findings argue that Ca²⁺ homeostasis is important in establishing the oocyte's competence to undergo maturation in preparation for fertilization and embryonic development.

Aurora kinase A, calcium, gamete biology, meiosis, oocyte development

¹Supported by National Institutes of Health grants GM-61829 (K.M.), HD35688 (A.M.M.), AG13081 (U.P.), and RR20146 (A.C.). C.P. is funded by grants from the CNRS and LNCC (équipe labellisée).

Correspondence: ²Khaled Machaca, Department of Physiology & Biophysics, 4301 West Markham St., Slot 505, University of Arkansas for Medical Sciences (UAMS), Little Rock, AR 72205. FAX: 501 686 8167; e-mail: kamachaca{at}uams.edu.