Int. J. Dev. Biol. 52: 743 - 752 (2008)

https://doi.org/10.1387/ijdb.072566gc

Vol 52, Issue 5-6

Special Issue: Fertilization

Two egg-derived molecules in sperm motility initiation and fertilization in the Pacific herring (Clupea pallasi)

Published: 1 July 2008

Gary N. Cherr^1,2,*, Masaaki Morisawa³, Carol A. Vines², Kaoru Yoshida⁴, Edmund H. Smith², Takahiro Matsubara⁵, Murali C. Pillai⁶, Frederick J. Griffin² and Ryuzo Yanagimachi⁷

¹Departments of Environmental Toxicology and Nutrition, University of California Davis, CA USA, ²Bodega Marine Laboratory, University of California Davis, USA, ³Department of Biology, Yamagata University, Japan, ⁴Biomedical Engineering Center, Toin University of Yokohama, Japan, ⁵Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Kushiro, Hokkaido, Japan, ⁶Department of Biology, Sonoma State University, CA USA and ⁷Institute for Biogenesis Research, University of Hawaii Medical School, Hawaii, USA

Abstract

Sperm of the Pacific herring are immotile at spawning. Two egg-derived molecules are capable of initiating sperm motility. One is herring sperm activating protein(s) (HSAPs) and the other is sperm motility initiation factor (SMIF). These two motility initiators differ in their location and association with the chorion, and in thier isoelectric points and molecular weights. In this study we have investigated the roles of these two inducers with respect to motility and fertilization. Using computer analysis of sperm motility, we found that HSAPs, as well as the C-terminal HSAPs peptide, elicit a linear motility pattern, while SMIF induced a highly circular and asymmetric pattern. HSAPs induced a two-fold increase in intracellular calcium, whereas SMIF induced a four-fold increase of motility initiation. SMIF-exposed sperm, preloaded with BAPTA-AM, showed a more linear motility and this motility trajectory decreased with their fertilizing capability. The difference in intracellular calcium levels between HSAPs and SMIF is consistent with the observed linear and circular motility. In the absence of SMIF, HSAPs do not support fertilization. Fertilization is rescued in these experiments if SMIF is reintroduced. We propose that diffusible HSAPs are not essential for fertilization, but enhance sperm-egg collisions via linear motility. SMIF, which is bound to the micropylar region of the chorion, is required for fertilization and induces circular motility that is a prerequisite for sperm to enter the micropylar canal and fertilize the egg.

Keywords

micropyle, intracellular calcium, sperm motility, chorion, motility initiation