Membrane Fusion in Gametes

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Three membrane fusion systems in the gametes of marine invertebrates were studied ; the acrosome reaction, sperm-egg fusion and exocytosis of cortical vesicles.1. Two signal moleules in starfish egg jelly, namely ARIS and SAP,are essential for the induction of acrosome reaction. Their structures were studied with reference to their biological activities. Major saccharide chains of ARIS had a repeating unit of pentasaccharide, [-4Xylb1-3Gala1-3FucSa1-4Fuca1-3FucSa1-]_n (FucS : Fuc-4-sulfate). Eleven glutamine-rich tetracontapeptides with a 25-residue ring formed by a disulfide linkage were identified as starfish SAPs.2. A zinc-metalloendoprotese is involved in the sperm-egg fusion of the ascidian, Ciona intestinalis. Such protease was purified from the sperm and characterized. The enzyme was immunocytochemically located in a certain region of sperm head.3. During maturation of starfish oocytes, cortical vesicles change their exocytotic capacity and pattern in response to fertilization. Ultrastructural changes of cortical vesicles in starfish oocytes were studied in relation to the oocyte maturation induced by 1-methyladenine. Fully-grown immature oocytes have a cytoplasmic network of cytokeratin filaments in the cortex. Heterotrimeric G protein, which is known to mediate 1-methyladenine stimulation of oocyte maturation, was immunocytochemically detected on the filaments as periodical bands of 0.7 mum long.