Novel enzyme provides sperm's spark of life. (Biology).

Biologists may have finally found what they call the "spark of life," a molecule in sperm that triggers a fertilized egg to begin developing.

Immediately after a sperm penetrates an egg, several waves of calcium ions flow out of the egg's stores of the ion. These calcium surges set off development of the fertilized egg. For more than a century, biologists have speculated that sperm must contain something that liberates this calcium. Several egg-activating factors have been proposed, but none has withstood scrutiny.

Because of its calcium-releasing role in some other cells, an enzyme called phospholipase C (PLC) was among the suspects. None of the known versions of PLC fits the bill as an egg activator, however.

Now, in the Aug. 15 Development, F. Anthony Lai of the University of Wales College of Medicine in Cardiff and his colleagues report the discovery of a new form of PLC that's present only in sperm. Moreover, when injected into an unfertilized egg, the enzyme stimulates calcium surges identical to those caused by sperm. This enzyme may provide a seemingly natural means of activating eggs in cloning or other forms of artificial reproduction, the scientists suggest.

Given the history of this issue, the role of the new PLC must be verified "10 times over," cautions Sergio Oehninger of the Jones Institute for Reproductive Medicine in Norfolk, Va.--J.T.