The soluble mammalian sperm factor protein that triggers Ca2+ oscillationsin eggs: Evidence for expression of mRNA(s) coding for sperm factor protein(s) in spermatogenic cells

At fertilisation in mammals the sperm initiates a series of Ca2+ oscillatio ns that activate development. One theory of signalling at fertilisation sug gests that the sperm contains a soluble protein factor that causes these Ca 2+ oscillations by entering the egg after sperm-egg membrane fusion. This t heory is supported by the finding that, in some species, injection of sperm protein extracts into eggs triggers a pattern of Ca2+ oscillations similar to those seen at fertilisation. So far, all the direct evidence for a sper m factor has been based upon the injection of soluble proteins from mature sperm. Here, we demonstrate that injection of mRNA extracted from hamster s permatogenic cells also leads to generation of prolonged Ca2+ oscillations in mouse eggs. The ability of spermatogenic cell mRNA to induce Ca2+ oscill ations is dependent upon translation into protein and also appears to be sp ecific to spermatogenic cells since injection of mRNA isolated from somatic tissues into eggs was ineffective. These data support the hypothesis that sperm contain a soluble, cytosolic protein factor that induces Ca2+ oscilla tions in eggs at fertilisation. These data are discussed in the light of ou r recent findings that suggest that the sperm factor possesses a phospholip ase C activity. (C) 2000 Editions scientifiques et medicales Elsevier SAS.