Editors' ChoiceReproduction

How a Sperm Turns On An Egg

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Science's STKE  23 Jul 2002:
Vol. 2002, Issue 142, pp. tw258-TW258
DOI: 10.1126/stke.2002.142.tw258

When a sperm joins with an egg, development is begun by a signal encoded in oscillations in the concentration of intracellular free calcium ([Ca2+]i) in the cytoplasm of the egg. Precisely how the interaction of egg and sperm triggers these oscillations in [Ca2+]i has been a matter of debate, but soluble extracts of sperm cells can reproduce the effect. The Ca2+ is released from intracellular stores in response to increased concentrations of inositol 1,4,5-trisphosphate (IP3), suggesting that a phosphatidylinositol-specific phospholipase C, which generates IP3 from phosphoinositides could be the culprit. But known PLCs can't substitute for sperm in activation of the egg. Saunders et al. now report that mouse sperm produce a previously uncharacterized isoform of PLC that they call PLCζ. Eggs microinjected with complimentary RNA encoding PLCζ showed oscillations in [Ca2+]i with temporal characteristics similar to those in normally fertilized eggs. Furthermore, the amount of PLCζ from just one sperm cell (about 50 fg) mimicked activation by a sperm, and depletion of PLCζ from sperm extracts by immunoprecipitation removed egg-activating activity. Thus, PLCζ from the sperm cytoplasm appears to be the key molecular determinant of egg activation. The authors note that their findings may be applied to treatment of male infertility or to egg activation for production of stem cells.

C. M. Saunders, M. G. Larman, J. Parrington, L. J. Cox, J. Royse, L. M. Blayney, K. Swann, F. A. Lai, PLCζ: A sperm-specific trigger of Ca2+ oscillations in eggs and embryo development. Development 129, 3533-3544 [Abstract] [Full Text]

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