Int. J. Dev. Biol. 52: 595 - 606 (2008)

https://doi.org/10.1387/ijdb.072550ad

Vol 52, Issue 5-6

Special Issue: Fertilization

Sperm-activating peptides in the regulation of ion fluxes, signal transduction and motility

Published: 1 July 2008

Alberto Darszon*^,1, Adán Guerrero¹, Blanca E. Galindo², Takuya Nishigaki¹ and Christopher D. Wood¹

¹Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, UNAM, Cuernavaca, Morelos, México and ²Centro de Investigación y de Estudios Avanzados del IPN, Unidad Monterrey, Apodaca, Nuevo León, México

Abstract

Echinoderm sperm use cyclic nucleotides (CNs) as essential second messengers to locate and swim towards the egg. Sea urchin sperm constitute a rich source of membrane-bound guanylyl cyclase (mGC), which was first cloned from sea urchin testis by the group of David Garbers. His group also identified speract, the first sperm-activating peptide (SAP) to be isolated from the egg investment (or egg jelly). This decapeptide stimulates sperm mGC causing a fast transient increase in cGMP that triggers an orchestrated set of physiological responses including: changes in: membrane potential, intracellular pH (pHi), intracellular Ca²⁺ concentration ([Ca²⁺]i) and cAMP levels. Evidence from several groups indicated that cGMP activation of a K⁺ selective channel was the first ion permeability change in the signaling cascade induced by SAPs, and recently the candidate gene was finally identified. Each of the 4 repeated, 6 trans-membrane segments of this channel contains a cyclic nucleotide binding domain. Together they comprise a single polypeptide chain like voltage-gated Na⁺ or Ca²⁺ channels. This new type of channel, named tetraKCNG, appears to belong to the exclusive club of novel protein families expressed only in sperm and its progenitors. SAPs also induce fluctuations in flagellar [Ca²⁺]i that correlate with changes in flagellar form and regulate sperm trajectory. The motility changes depend on [Ca²⁺]i influx through specific Ca²⁺ channels and not on the overall [Ca²⁺]i in the sperm flagellum. All cilia and flagella have a conserved axonemal structure and thus understanding how Ca²⁺ regulates cilia and flagella beating is a fundamental question.

Keywords

sea urchin, calcium, potassium channel, cyclic nucleotides, flagella