[
Science,
1996]
In creatures from worms to people, it takes two sexes to reproduce, but it's often the female who gets stuck with the real work of childbearing. This division of labor is even mirrored in sperm and eggs. The unfertilized eggs of fruit flies, for example, already contain the molecular signals needed to direct one of the first events in embryonic growth, the creation of distinct body segments. The paternal contribution to early development, in contrast, seems paltry. Sperm carries nuclear material and organelles called centrosomes - organizing sites for cell division - that come into play later on, but no biochemical factors that guide early embryogenesis have been traced back to the father. In the January issue of the journal Development, however, molecular biologist Heidi Browning of the University of Colorado and developmental geneticist Susan Strome of Indiana University report that SPE-11, a protein produced only in the sperm of the nematode Caenorhabditis elegans, may play a crucial role during the first few minutes after the embryo is fertilized.