Original article The soluble mammalian sperm factor protein that triggers Ca 2+ oscillations in eggs: Evidence for expression of mRNA(s) coding for sperm factor protein(s) in spermatogenic cells John Parrington a* , F. Anthony Lai b , Karl Swann a a Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK b Division of Medicine-Cardiology, University of Wales College of Medicine, Heath Park, Cardiff CF14 4XN, UK Received 17 February 2000; accepted 13 April 2000 At fertilisation in mammals the sperm initiates a series of Ca 2+ oscillations that activate development. One theory of signalling at fertilisation suggests that the sperm contains a soluble protein factor that causes these Ca 2+ oscillations by entering the egg after sperm–egg membrane fusion. This theory is supported by the finding that, in some species, injection of sperm protein extracts into eggs triggers a pattern of Ca 2+ oscillations similar to those seen at fertilisation. So far, all the direct evidence for a sperm factor has been based upon the injection of soluble proteins from mature sperm. Here, we demonstrate that injection of mRNA extracted from hamster spermatogenic cells also leads to generation of prolonged Ca 2+ oscillations in mouse eggs. The ability of spermatogenic cell mRNA to induce Ca 2+ oscillations is dependent upon translation into protein and also appears to be specific 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 Ca 2+ oscillations in eggs at fertilisation. These data are discussed in the light of our recent findings that suggest that the sperm factor possesses a phospholipase C activity. © 2000 Éditions scientifiques et médicales Elsevier SAS sperm / egg / calcium / mRNA 1. INTRODUCTION At fertilisation in all species studied development is triggered by a sperm-induced increase in the egg intracellular Ca 2+ concentration (Whitaker and Swann, 1993; Miyazaki et al. 1993; Stricker, 1999). In sea urchin, frog and fish eggs, a single transient of Ca 2+ release is triggered during egg activation at fertilisation (Stricker, 1999). In a number of other species, including those of mammals, ascidians and nemertean worms, the fertil- ising sperm induces a distinctive series of intracellular Ca 2+ oscillations in the egg (Miyazaki et al., 1993; Swann and Ozil, 1994; Stricker, 1999). In mammals, the Ca 2+ oscillations are noticeably prolonged, since they persist for many hours after sperm penetration (Swann and Ozil, 1994). Such long lasting Ca 2+ oscillations are * Correspondence and reprints: j.parrington@ucl.ac.uk Abbreviations: PLC, phospholipase C; PI, phosphatidylinositol; InsP 3 , inositol 1,4,5-trisphosphate; Ca 2+ , calcium; G protein, guanine-nucleotide binding protein; SH2 domain, src homology 2 domain; mRNA, messenger ribonucleic acid; RNP, messenger ribonucleoprotein particle; UTR, untranslated region; GV, germi- nal vesicle. Biology of the Cell 92 (2000) 267-275 © 2000 Éditions scientifiques et médicales Elsevier SAS. All rights reserved S0248490000010649/FLA Spermatogenic cell mRNA triggers Ca 2+ oscillations in eggs Parrington et al.