Analysis of the sperm motility initiation substances in newt egg-jelly

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Newt undergoes internal fertilization. Sperm are directly inseminated on the surface of egg-jelly in the cloaca of the female. We have reported that most sperm begin to move rapidly by the treatment of egg-jelly extract (JE) of the newt, cynops pyrrhogaster, and the sperm motility initiation factor (SMIS) in the JE is responsible for the rapid initiation of sperm motility. Egg-jelly also contains cations that can involve in the regulation of the sperm motility. In this study, we elucidated the role of those factors under the physiological condition of egg-jelly. The reconstructed ionic solution (RIS) was prepared according to the estimated pH and ionic concentrations. When dry sperm were added to the JE-RIS, most of them began to move within 3 min. A K^+-channel blocker, verapamil, and a Ca^<2+>-channel blocker, charlbdotoxin, specifically inhibited the rapid initiation of sperm motility by JE, suggesting that those channels participate in the initiation of sperm motility caused by the SMIS.Whereas, sperm motility was induced by the decrease of osmolality in the other amphibians, including the primitive species of urodeles, that undergo external fertilization. Sperm of C. pyrrhogaster also begins to move under low osmolality. In this study, when dry sperm were added in water, they rapidly began to move like those in the JE. However, the initiation of sperm motility induced by water was independent of pH within the range of 7 to 8.5 while that induced by SMIS was strengthened under the high pH condition. Furthermore, water-induced sperm motility did not make vigorous within 10 min while most sperm in the JE vigorously moved in 10 min. Two distinct mechanisms for the regulation of sperm motility may be equipped in the sperm of urodeles, which may allow sperm to begin to move under the distinct conditions in the species-specific fertilization modes.