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Ca2+ oscillations at fertilization in mammals are regulated by the formation of pronuclei

Marangos, P; FitzHarris, G; Carroll, J; (2003) Ca2+ oscillations at fertilization in mammals are regulated by the formation of pronuclei. DEVELOPMENT , 130 (7) 1461 - 1472. 10.1242/dev.00340.

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Abstract

In mammals, the sperm triggers a series of cytosolic Ca2+ oscillations that continue for similar to4 hours, stopping close to the time of pronucleus formation. Ca2+ transients are also seen in fertilized embryos during the first mitotic division. The mechanism that controls this pattern of sperm-induced Ca2+ signalling is not known. Previous studies suggest two possible mechanisms: first, regulation of Ca2+ oscillations by M-phase kinases; and second, regulation by the presence or absence of an intact nucleus. We describe experiments in mouse oocytes that differentiate between these mechanisms. We find that Ca2+ oscillations continue after Cdk1-cyclin B1 activity falls at the time of polar body extrusion and after MAP kinase has been inhibited with UO126. This suggests that M-phase kinases are not necessary for continued Ca2+ oscillations. A role for pronucleus formation in regulating Ca2+ signalling is demonstrated in experiments where pronucleus formation is inhibited by microinjection of a lectin, WGA, without affecting the normal inactivation of the M-phase kinases. In oocytes with no pronuclei but with low M-phase kinase activity, sperm-induced Ca2+ oscillations persist for nearly 10 hours. Furthermore, a dominant negative importin P that inhibits nuclear transport, also prevents pronucleus formation and causes Ca2+ oscillations that continue for nearly 12 hours. During mitosis, fluorescent tracers that mark nuclear envelope breakdown and the subsequent reformation of nuclei in the newly formed two-cell embryo establish that Ca2+ oscillations are generated only in the absence of a patent nuclear membrane. We conclude by suggesting a model where nuclear sequestration and release of a Ca2+-releasing activity contributes to the temporal organization of Ca2+ transients in meiosis and mitosis in mice.

Type: Article
Title: Ca2+ oscillations at fertilization in mammals are regulated by the formation of pronuclei
DOI: 10.1242/dev.00340
Keywords: Ca2+ signalling, fertilization, pronucleus, mouse oocytes, meiosis, mitosis, INDUCED CALCIUM OSCILLATIONS, ACTIVATED PROTEIN-KINASE, MOUSE EGGS, CELL-CYCLE, PARTHENOGENETIC DEVELOPMENT, METAPHASE ARREST, PHOSPHOLIPASE-C, RABBIT OOCYTES, SPERM, MEIOSIS
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Cell and Developmental Biology
URI: http://discovery.ucl.ac.uk/id/eprint/185499
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