Substances for the Initiation of Sperm Motility in Egg-Jelly of the Japanese Newt, Cynops pyrrhogaster

Abstract

The initiation of sperm motility is regulated by certain factors, including a change of osmolality or ion concentration. The cue for the initiation of sperm motility is unique to species and suits the environment in which the fertilization occurs.In the newt, Cynops pyrrhogaster, eggs are fertilized in the cloaca of the female with sperm stored in the sperm reservoir. In this study, we investigated possible factors initiating sperm motility in this unique environment. Sperm of C. pyrrhogaster could be initiated to move by a decrease of osmolality. However, eggs were fertilized with dry sperm and developed to four-cell stage embryos without immersion in solution. They continued to develop normally to the tail-bud stage when placed in Steinberg's salt solution after fertilization. These results indicate that sperm motility was initiated without the change of osmolality around sperm. In egg-jelly extract, the activity for the initiation of sperm motility was strong and heat stable, but disappeared by proteinase treatment. ICP luminescence analysis revealed that sodium, potassium, calcium and magnesium ions were major cations in egg-jelly. The monovalent cations showed the activity for the initiation of sperm motility in high concentration at high pH, and this activity become stronger by the addition of calcium ion. However, the reconstructed ionic solution that was prepared according to the concentrations of these four ions and pH in egg-jelly did not show the activity as strong as egg-jelly extract. These results suggest that the proteinacious factor and cations in egg-jelly are significant to regulate the initiation of sperm motility in C. pyrrhogaster.