Signal transduction mechanisms regulating ion fluxes in the sea urchin sperm

Abstract

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 modulated 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 signaling systems depend on plasma membrane ion permeability and involve an alteration of second messenger levels, changes of membrane potential and intracellular Ca2+, Na+ and pH, along with changes in sperm morphology in the case of the acrosome reaction (AR). New procedures to elucidate the signaling pathways implicated in sperm ion transport have expanded the opportunities 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.

Particulate and soluble adenylyl cyclases participate in the sperm acrosome reaction

“…Our findings indicate that both susAC and tmACs participate in the egg-jelly induced sea urchin sperm AR. In this species, both the natural inducer of the AR and speract, elevate cAMP and cause different [Ca 2+ ] i spatio-temporal changes [1,13]. How do sperm discern between these signals?…”

“…Why AC activity, cAMP levels, and cyclic AMP-dependent protein kinase (PKA) activity increase [11] Sea urchin sperm were believed to have only one type of AC and no G proteins [11,13].…”

“…In contrast, sAC is stimulated by bicarbonate [6] and Ca 2+ [7,8]. In addition to sAC, mouse [9] and human [10] sperm apparently also contain tmACs.Why AC activity, cAMP levels, and cyclic AMP-dependent protein kinase (PKA) activity increase [11] Sea urchin sperm were believed to have only one type of AC and no G proteins [11,13].Recently an ortholog of the mammalian sperm sAC was cloned and sequenced from a sea urchin Strongylocentrotus purpuratus testis cDNA library (susAC). Its activity is higher in the presence of Mn 2+ than Mg 2+ , and is stimulated by pH [18].…”

“…Two eggjelly layer components: speract, a decapeptide that modulates motility and fucose sulphate polymer, the natural inducer of the AR, cause cAMP elevations. Therefore, AC activation could be involved in these two important sperm processes [1,13,16,17].…”

“…Sea urchin sperm were believed to have only one type of AC and no G proteins [11,13]. Recently an ortholog of the mammalian sperm sAC was cloned and sequenced from a sea urchin Strongylocentrotus purpuratus testis cDNA library (susAC).…”