卵細胞と細胞内カルシウムの生理学的研究(最終講義)

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My last lecture described our 40-year experience with original physiological studies on egg cells. In 1971, we found Na^+ and Ca^<2+> dependent action potentials to occur in unfertilized tunicate eggs. We also discovered that starfish eggs generate Ca^<2+> dependent action potentials and exhibit an outward rectifying K^+ current, which develops during oocyte maturation. These properties were implicated in the electrical polyspermy block due to overshoot of the fertilization potential. In 1981, we recorded long-lasting repetitive hyperpolarizing responses during fertilization of hamster eggs. Later experiments with Ca^<2+> imaging confirmed repetitive increases in intracellular Ca^<2+>, referred to as Ca^<2+> oscillations, which trigger egg activation noted by resumption of the second meiosis. In 1992, we showed that each Ca^<2+> rise is due to Ca^<2+> release from the endoplasmic reticulum through inositol 1, 4, 5-trisphosphate receptor (IP_3R), forming a Ca^<2+> wave based on Ca^<2+> -induced Ca^<2+> release. Evidence indicated that repeated Ca^<2+> release is caused by cytoplasmic sperm factor driven into the ooplasm. A current strong candidate as the sperm factor is a novel sperm-specific type of phospholipase C-zeta (PLCζ), an IP_3-producing enzyme. The characteristics of PLCζ have been extensively analyzed since 2002. Thus, I experienced unexpected discoveries and subsequent great development of later studies.
東京女子医科大学の論文