Signal Transduction 2007, 7, 103 – 117 C. Beltrµn et al. 103 Review Article Signal transduction mechanisms regulating ion fluxes in the sea urchin sperm Carmen Beltrµn 1 , Blanca Estela Galindo 2 , Esmeralda Rodríguez-Miranda 3 , Daniel Sµnchez 2 1 Departamento de GenØtica del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de MØxico, Cuernavaca, Morelos, MØxico 2 Cinvestav, Unidad Monterrey, Monterrey, Nuevo León, MØxico 3 Instituto Tecnológico Superior de Irapuato ITESI, Irapuato, Guanajuato, MØxico Ion permeability changes involving ion channels and transporters are essential for fertilization, since they are key elements in sperm-egg signaling and environmental sensing. Changes modu- lated by external factors and components from the outer layer of the homologous egg, like the sperm-activating peptides and the fucose-sulfate glycoconjugate, trigger complex signaling systems in the sperm that modulate how sperm swim, find the egg and fertilize it. These signa- ling systems depend on plasma membrane ion permeability and involve an alteration of second messenger levels, changes of membrane potential and intracellular Ca 2+ , Na + and pH, along with changes in sperm morphology in the case of the acrosome reaction (AR). New procedures to elu- cidate the signaling pathways implicated in sperm ion transport have expanded the opportuni- ties to dissect sperm-egg signaling revealing how sperm ion channels participate in activation, motility, chemotaxis, and the AR. The sperm signaling pathways involve a large variety of ion channels and transporters, which are discretely localized and finely orchestrated to play specific roles that define the elaborate performance of sperm and allow a successful fertilization. In this review we will focus on the signaling molecules involved in the final aim of the sperm, to reach and fertilize the egg. Keywords: Acrosome reaction / Fertilization / Motility / Sea urchin / Sperm / Received: December 14, 2006; accepted: December 25, 2006 DOI 10.1002/sita.200600129 Introduction Fertilization is an essential event in the life of organisms dependent on sexual reproduction for the generation of a new individual. The sea urchin sperm is a highly specia- lized cell that receives messages from the egg to success- fully achieve fusion and fertilization. Diffusible compo- nents from the extracellular matrix of the egg influence the sperm and prepare it for fertilization. Two major pro- cesses are triggered by the egg components. First, they regulate how sperm swim to find the egg involving che- mokinetic and chemotactic effects, and second, when the sperm is close enough to the egg, the sperm undergo the AR, an exocytotic event essential for fusion with the egg membrane and the transfer of the sperm genetic material. The activation of receptors in the sperm mem- Correspondence: Carmen Beltrµn, Departamento de GenØtica del De- sarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de MØxico, Av. Universidad 2001, Col. Chamilpa, C. P. 62210. Cuernavaca, Morelos, MØxico E-mail: beltran@ibt.unam.mx Fax: +52 777 317-23-88 Abbreviations: AC, adenylyl cyclase; AR, acrosome reaction; BLMs, black lipid membranes; Cav, voltage-dependent calcium channel; DAG, i 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.signaltrans.com diacylglycerol; DIDS, 4,49-diisothiocyano-2,29-stilbendisulfonic acid; EJ, egg jelly; Em, membrane potential; FSP, fucose sulfate polymer; GC, guanylyl cyclase; HCN, hyperpolarization-activated and cyclic nucleotide- gated channel; HCO3 – , bicarbonate; IP3, inositol 1,4,5, triphosphate; IP3R, IP3 receptor; PA, phosphatidic acid; PC1, polycystin-1; PDE, phospho- diesterase; pHi, intracellular pH; PKA, cAMP-dependent protein kinase; PLC, phospholipase C; PLD, phospholipase D; SAP, sperm-activating peptide; suREJ, sea urchin sperm receptor for egg jelly; TRP, transient receptor potential channel.