Peptide-induced hyperactivation-like vigorous flagellar movement in starfish sperm

Abstract

Asterosap, a sperm-activating peptide (SAP) from the starfish egg jelly coat, is diffusible and controls a cGMP-signalling pathway in starfish sperm in the same manner as resact, a potent chemoattracting SAP in sea urchins. This fact suggests that asterosap may serve as a chemoattractant like resact at concentrations with appropriate gradients. Since asterosap is one of three egg jelly components, which in concert induce the acrosome reaction, it is still worthwhile to evaluate how asterosap modulates sperm motility prior to this reaction. We analysed the flagellar movement of sperm of the starfish Aphelasterias japonica in artificial seawater (ASW) containing the asterosap isoform P15 at 1 micromol l(-1). We found that sperm swim straighter with more symmetrical flagellar movement in P15 than in ASW, but without any significant difference in the flagellar beat frequency and the swimming velocity. The flagellar movement is, however, dramatically different between sperm firmly attached to the solid surface by the head in P15 and those attached in ASW: in P15 the flagellum bends to a greater extent, with higher curvature and with higher shear angle up to a right angle to the flagellar wave axis, and beats at an increased frequency. The vigorous flagellar movement of sperm, which can be activated when sperm are placed in high-load circumstances just as entering into a jelly layer, may increase propulsive forces and hydrodynamic resistances, allowing sperm to undergo the acrosome reaction as effectively as possible.

Eggs regulate sperm flagellar motility initiation, chemotaxis and inhibition in the coralAcropora digitifera,A. gemmiferaandA. tenuis

“…Sea urchin sperm swim straight in the presence of sperm-activating peptide (SAP) isoform P15 (Shiba et al, 2006). These reactions were almost similar among three Acropora species.…”

Asterosap, an Egg Jelly Peptide, Elevate Intracellular Ca²⁺ and Activate the Motility of Spermatozoa

“…Shiba et al (2006) reported that starfish (Aphelasterias japonica) spermatozoa swam along circular paths with the head oscillating synchronously. Our studies on A. amurensis found that spermatozoa in ASW also swam along a circular path but beat frequency increased those in asterosap ( Fig.…”

Regulation of the starfish sperm acrosome reaction by cGMP, pH, cAMP and Ca2+

“…Resact is a chemoattractant for sperm and it evokes elevations of intracellular Ca 2+ ([Ca 2+ ]i) in the flagellum (Garbers & Kopf, 1989;Kaupp et al, 2008). As in the case of sea urchin, in starfish, asterosap is also a chemotactic agent for sperm , Shiba et al, 2006. The increase in [Ca 2+ ]i elicits a turn in the sperm trajectory followed by a period of straight swimming called "turnand run" (Boehmer et al, 2005).…”