CALCIUM SIGNALING AT FERTILIZATION

It is generally agreed that fertilization in deuterostomes is accompan ied by a large intracellular calcium wave that triggers the onset of d evelopment, but we still do not know exactly how the calcium wave is g enerated. The question has two parts: how does interaction of sperm an d egg initiate the calcium wave, and how does the calcium wave spread across the cell? Two provisional answers are available to the first pa rt of the question, one involving receptor-G-protein interactions of t he sort that mediate transmembrane signal transduction in somatic cell s, the other injection of an activating messenger when sperm and egg f use. Both these ideas are being actively pursued; the dialectic is pro ductive, albeit no synthesis is in sight. We discuss their strengths a nd weaknesses. The second part of the question can now be much more pr ecisely formulated: thanks to the recent flush of interest in calcium waves in somatic cells, new ideas and new experimental tools are avail able. The work on somatic cells repays a debt to eggs, where the basic properties of calcium waves were first set out, ten years before they turned up in somatic cells.