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

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  • Petros Marangos
    Department of Physiology, UCL, Gower Street, London WC1E 6BT, UK
  • Greg FitzHarris
    Department of Physiology, UCL, Gower Street, London WC1E 6BT, UK
  • John Carroll
    Department of Physiology, UCL, Gower Street, London WC1E 6BT, UK

説明

<jats:p>In mammals, the sperm triggers a series of cytosolic Ca2+oscillations that continue for ∼4 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 β 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.</jats:p>

収録刊行物

  • Development

    Development 130 (7), 1461-1472, 2003-04-01

    The Company of Biologists

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