Development, Vol 124, Issue 1 233-241, Copyright © 1997 by Company of Biologists

JOURNAL ARTICLES

Sperm-egg fusion is the prelude to the initial Ca2+ increase at fertilization in the mouse

Y Lawrence, M Whitaker and K Swann
Department of Anatomy and Developmental Biology, University College London, UK.

Fusion of sperm and egg plasma membranes is an early and essential event at fertilization but it is not known if it plays a part in the signal transduction mechanism that leads to the oscillations in the cytoplasmic free Ca2+ concentration ([Ca2+]i) that accompany mammalian egg activation. We have used two independent fluorescence methods and confocal microscopy to show that cytoplasmic continuity of egg and sperm precedes the onset of the first [Ca2+]i increase in mouse eggs. The Ca2+ indicator dye Ca2+-green dextran was microinjected and its transfer from egg to sperm was monitored. We found that it occurred before, and without a requirement for, any detectable [Ca2+]i increase in the egg. In separate experiments [Ca2+]i changes were recorded in populations of eggs, using fura red, and the eggs fixed at various times after some of the eggs had shown a [Ca2+]i transient. Fusion of the sperm and egg was then assessed by Hoechst dye transfer. All eggs that showed a [Ca2+]i increase had a fused sperm but more than half of the eggs contained a sperm but had not undergone a [Ca2+]i increase. These data indicate that sperm-egg fusion precedes [Ca2+]i changes and we estimate that the elapsed time between sperm-egg fusion and the onset of the [Ca2+li oscillations is 1-3 minutes. Finally, sperm-egg fusion was prevented by using low pH medium which reversibly prevented [Ca2+]i oscillations in eggs that had been inseminated. This was not due to disruption of signalling mechanisms, since [Ca2+]i changes still occurred if low pH was applied after the onset of oscillations at fertilization. [Ca2+]i changes also occurred in eggs in low pH in response to the muscarinic agonist carbachol. These data are consistent with the idea that the [Ca2+]i signals that occur in mammalian eggs at fertilization are initiated by events that are closely coupled to the fusion of the sperm and egg membranes.

This article has been cited by other articles:

				S.-Y. Yoon and R. A Fissore Release of phospholipase C {zeta}and [Ca2+]i oscillation-inducing activity during mammalian fertilization Reproduction, November 1, 2007; 134(5): 695 - 704. [Abstract] [Full Text] [PDF]

				N. Yoshida, M. Amanai, T. Fukui, E. Kajikawa, M. Brahmajosyula, A. Iwahori, Y. Nakano, S. Shoji, J. Diebold, H. Hessel, et al. Broad, ectopic expression of the sperm protein PLCZ1 induces parthenogenesis and ovarian tumours in mice Development, November 1, 2007; 134(21): 3941 - 3952. [Abstract] [Full Text] [PDF]

				M.G. Larman, M.G. Katz-Jaffe, C.B. Sheehan, and D.K. Gardner 1,2-propanediol and the type of cryopreservation procedure adversely affect mouse oocyte physiology Hum. Reprod., January 1, 2007; 22(1): 250 - 259. [Abstract] [Full Text] [PDF]

				K. Morozumi, T. Shikano, S. Miyazaki, and R. Yanagimachi From the Cover: Simultaneous removal of sperm plasma membrane and acrosome before intracytoplasmic sperm injection improves oocyte activation/embryonic development PNAS, November 21, 2006; 103(47): 17661 - 17666. [Abstract] [Full Text] [PDF]

				N T Rogers, G Halet, Y Piao, J Carroll, M S H Ko, and K Swann The absence of a Ca2+ signal during mouse egg activation can affect parthenogenetic preimplantation development, gene expression patterns, and blastocyst quality Reproduction, July 1, 2006; 132(1): 45 - 57. [Abstract] [Full Text] [PDF]

				M. Whitaker Calcium at Fertilization and in Early Development Physiol Rev, January 1, 2006; 86(1): 25 - 88. [Abstract] [Full Text] [PDF]

				S. Toth, D. Huneau, B. Banrezes, and J.-P. Ozil Egg activation is the result of calcium signal summation in the mouse Reproduction, January 1, 2006; 131(1): 27 - 34. [Abstract] [Full Text] [PDF]

				M. G Larman, C. B Sheehan, and D. K Gardner Calcium-free vitrification reduces cryoprotectant-induced zona pellucida hardening and increases fertilization rates in mouse oocytes Reproduction, January 1, 2006; 131(1): 53 - 61. [Abstract] [Full Text] [PDF]

				C. Malcuit, J. G. Knott, C. He, T. Wainwright, J. B. Parys, J. M. Robl, and R. A. Fissore Fertilization and Inositol 1,4,5-Trisphosphate (IP3)-Induced Calcium Release in Type-1 Inositol 1,4,5-Trisphosphate Receptor Down-Regulated Bovine Eggs Biol Reprod, July 1, 2005; 73(1): 2 - 13. [Abstract] [Full Text] [PDF]

				J. G. Knott, M. Kurokawa, R. A. Fissore, R. M. Schultz, and C. J. Williams Transgenic RNA Interference Reveals Role for Mouse Sperm Phospholipase C{zeta} in Triggering Ca2+ Oscillations During Fertilization Biol Reprod, April 1, 2005; 72(4): 992 - 996. [Abstract] [Full Text] [PDF]

				M. G. Larman, C. M. Saunders, J. Carroll, F. A. Lai, and K. Swann Cell cycle-dependent Ca2+ oscillations in mouse embryos are regulated by nuclear targeting of PLC{zeta} J. Cell Sci., May 15, 2004; 117(12): 2513 - 2521. [Abstract] [Full Text] [PDF]

				S. J. Bedford, M. Kurokawa, K. Hinrichs, and R. A. Fissore Patterns of Intracellular Calcium Oscillations in Horse Oocytes Fertilized by Intracytoplasmic Sperm Injection: Possible Explanations for the Low Success of This Assisted Reproduction Technique in the Horse Biol Reprod, April 1, 2004; 70(4): 936 - 944. [Abstract] [Full Text] [PDF]

				E. Tosti and R. Boni Electrical events during gamete maturation and fertilization in animals and humans Hum. Reprod. Update, January 1, 2004; 10(1): 53 - 65. [Abstract] [Full Text] [PDF]

				M. Kurokawa and R. A. Fissore ICSI-generated mouse zygotes exhibit altered calcium oscillations, inositol 1,4,5-trisphosphate receptor-1 down-regulation, and embryo development Mol. Hum. Reprod., September 1, 2003; 9(9): 523 - 533. [Abstract] [Full Text] [PDF]

				C. Tatone, S. Delle Monache, R. Iorio, D. Caserta, M. Di Cola, and R. Colonna Possible role for Ca2+ calmodulin-dependent protein kinase II as an effector of the fertilization Ca2+ signal in mouse oocyte activation Mol. Hum. Reprod., August 1, 2002; 8(8): 750 - 757. [Abstract] [Full Text] [PDF]

				G. Halet, R. Tunwell, T. Balla, K. Swann, and J. Carroll The dynamics of plasma membrane PtdIns(4,5)P2 at fertilization of mouse eggs J. Cell Sci., May 15, 2002; 115(10): 2139 - 2149. [Abstract] [Full Text] [PDF]

				J. G. Knott, K. Poothapillai, H. Wu, C. L. He, R. A. Fissore, and J. M. Robl Porcine Sperm Factor Supports Activation and Development of Bovine Nuclear Transfer Embryos Biol Reprod, April 1, 2002; 66(4): 1095 - 1103. [Abstract] [Full Text] [PDF]

				A McDougall, M Levasseur, A. O'Sullivan, and K. Jones Cell cycle-dependent repetitive Ca(2+ )waves induced by a cytosolic sperm extract in mature ascidian eggs mimic those observed at fertilization J. Cell Sci., January 10, 2000; 113(19): 3453 - 3462. [Abstract] [PDF]

				C. Sette, A. Bevilacqua, R. Geremia, and P. Rossi Involvement of Phospholipase Cgamma 1 in Mouse Egg Activation Induced by a Truncated Form of the C-kit Tyrosine Kinase Present in Spermatozoa J. Cell Biol., August 24, 1998; 142(4): 1063 - 1074. [Abstract] [Full Text] [PDF]

				K. Jones, C Soeller, and M. Cannell The passage of Ca2+ and fluorescent markers between the sperm and egg after fusion in the mouse Development, January 12, 1998; 125(23): 4627 - 4635. [Abstract] [PDF]

				A. Galione, K. T. Jones, F. A. Lai, and K. Swann A Cytosolic Sperm Protein Factor Mobilizes Ca2+ from Intracellular Stores by Activating Multiple Ca2+ Release Mechanisms Independently of Low Molecular Weight Messengers J. Biol. Chem., November 14, 1997; 272(46): 28901 - 28905. [Abstract] [Full Text] [PDF]

				D. J. Carroll, C. S. Ramarao, L. M. Mehlmann, S. Roche, M. Terasaki, and L. A. Jaffe Calcium Release at Fertilization in Starfish Eggs Is Mediated by Phospholipase Cgamma J. Cell Biol., September 22, 1997; 138(6): 1303 - 1311. [Abstract] [Full Text] [PDF]

				C Digonnet, D Aldon, N Leduc, C Dumas, and M Rougier First evidence of a calcium transient in flowering plants at fertilization Development, January 8, 1997; 124(15): 2867 - 2874. [Abstract] [PDF]