Molecular Biological Studies on the Regulation of Sperm Motility

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We found that during transit of sperm from the testis to the sperm duct of salmonid fishes, increases in external pH and HCO_3 cause increases in pH_i and cAMP which affect the motile apparatus of flagellum, axoneme, causing the acquisition of the potential for sperm motility. Concerning the initiation of sperm motility in salmonid fishes at spawning, we obtained the first finding that control of flagellar movement occurs at the limited portion i.e.basal part of flagellum using prepared monoclonal antibodies of the 15kDa motility initiating phosphoprotein (MIPP) with a molecular weight of 15KDa. In the freshwater cyprinid fishes and marine fishes, we showed the different sperm motility initiation mechanisms ; Decrease or increase in external osmolalities causes increase or decrease in K^+_i causing the initiation axonemal movement to confer motility to spermatozoa. In the activation of sperm motility, the substance released from herring egg which activate sperm motility were purified by using gel-filtration and isoelectric focusing chromatograpies and identified 5 proteins with MW of 8.1 KDa and with Pl of 4.9-5.4. cDNA of the HSAP with Pl 5.1 was cloned and amino acid sequence with 73 amino acid residues was defined. The HSAP is resemble to typsin inhibitors, suggesting that interaction between trypsin inhibitor-like HSAPs and trypsin-like receptor on the surface of spermatozoa causes the signal transduction mechanism which triggers the activation of herring sperm motility. The sperm activating and attracting factor (SAAF) released from the egg of Ciona was purified using several HPLC chromatographies and it was concluced that one molecule has two functions, sperm activation and sperm attraction. Further findings suggest that sperm activation requires both Ca^<2+> and cAMP,but sperm chemotaxis needs only Ca^<2+>, suggesting that one molecule triggers two different signal transduction systems.