Mechanism for the regulation of sperm flagellar motility by ubiquitin/proteasome system

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Ubiquitin/proteasome system is involved in the degradation of short life-time proteins and the regulation of several important intracellular processes. It also plays important roles in the process of fertilization, such as sperm-egg interaction and the regulation of sperm motility. In this research several approach were conducted to reveal the mechanism for the regulation of sperm motility by this system, with salmonid fish and ascidian as experimental materials. First, apart from a dynein light chain which is closely related to sperm proteasome system, I have identified a novel 15 kDa protein of which phosphorylation is regulated by proteasome. The protein is shown to be located at the base of the flagellum. Second, the proteasome system is shown to be upstream regulated by membrane hyperpolarization exerted by a pottasium channel. Third, research was conducted to reveal if ubiquitinated proteins were present in broad range of organisms. It was shown that salmonid fish sperm contain no detectable ubiquitinated protein, however ascidian sperm show high content in ubiquitinated proteins. In ascidian sperm, ubiquitin is localized in the region between sperm nucleus and mitochondrion. These suggest that ubiquitin is involved not in the general aspect of sperm function such as sperm motility but in ascidian-specific process, most likely in mitochndrial discrimination observed at fertilization. Finally several genes for ubiquitin/ proteasome system have been isolated by overall anaysis of genes expressed in Ciona testis. The 12,000 ESTs so far analyzed contain several enzymes for protein ubiquitination and components of 26 S proteins. These cDNAs would surely provide a powerful tools for further research on the function of ubiquitin/ proteasome system in sperm cells.