Sci. STKE, 23 July 2002
Reproduction How a Sperm Turns On An Egg
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 PLC. Eggs microinjected with complimentary RNA encoding PLC showed oscillations in [Ca2+]i with temporal characteristics similar to those in normally fertilized eggs. Furthermore, the amount of PLC from just one sperm cell (about 50 fg) mimicked activation by a sperm, and depletion of PLC from sperm extracts by immunoprecipitation removed egg-activating activity. Thus, PLC 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, PLC: A sperm-specific trigger of Ca2+ oscillations in eggs and embryo development. Development 129, 3533-3544 [Abstract] [Full Text]
Citation: How a Sperm Turns On An Egg. Sci. STKE 2002, tw258 (2002).
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