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Volume 272, Number 46, Issue of November 14, 1997 pp. 28901-28905
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

A Cytosolic Sperm Protein Factor Mobilizes Ca²⁺ from Intracellular Stores by Activating Multiple Ca²⁺ Release Mechanisms Independently of Low Molecular Weight Messengers

(Received for publication, August 29, 1997)

Antony Galione , Keith T. Jones ^¶ , F. Anthony Lai and Karl Swann ^¶

From the  University Department of Pharmacology, Oxford University, Mansfield Road, Oxford OX1 3QT, the  Medical Research Council National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, and the ^¶ Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom

Ca²⁺ oscillations can be induced in mammalian eggs and somatic cells by microinjection of a cytosolic sperm protein factor. The nature of the sperm factor-induced Ca²⁺ signaling was investigated by adding sperm protein extracts to homogenates of sea urchin eggs, which contain multiple classes of Ca²⁺ release mechanisms. We show that the sperm factor mobilizes Ca²⁺ from non-mitochondrial Ca²⁺ stores in egg homogenates after a distinct latency. This latency is abolished by preincubation of sperm extracts with egg cytosol. The preincubation step is highly temperature-dependent and generates a high molecular weight, protein-based Ca²⁺-releasing agent that can also mobilize Ca²⁺ from purified egg microsomes. This Ca²⁺ release appears to be mediated via both inositol 1,4,5-trisphosphate and ryanodine receptors, since homologous desensitization of these two release mechanisms by their respective agonists inhibits further release by the sperm factor. However, sperm factor-induced Ca²⁺ release by these channels is independent of inositol 1,4,5-trisphosphate or cADPR since antagonists of either of these two messengers did not block the Ca²⁺ release effected by the sperm factor. The sperm protein factor may cause Ca²⁺ release via an enzymatic step that generates a protein-based Ca²⁺-releasing agent.

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