Masaaki Morisawa

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Spermatozoa that are quiescent in electrolyte and nonelectrolyte solutions isotonic to seminal plasma show motility when the semen is diluted with hypotonic solution in freshwater teleosts (four species tested) and with hypertonic solution in marine teleosts (five species tested). Decrease or increase, respectively, in osmolality of the environment may be(More)
Chemotactic swimming behaviors of spermatozoa toward an egg have been reported in various species. The strategies underlying these behaviors, however, are poorly understood. We focused on two types of chemotaxis, one in the siphonophores and the second in the ascidians, and then proposed two models based on experimental data. Both models assumed that the(More)
The sperm-activating and -attracting factor released from the eggs of the ascidians Ciona intestinalis and Ciona savignyi requires extracellular Ca(2+) for activating sperm motility and eliciting chemotactic behavior of the activated sperm toward the egg. Here, we show that modulators of the store-operated Ca(2+) channel, SK&F96365, Ni(2+),(More)
The larvae of the ascidian Ciona intestinalis from which the chorion with the test cells and follicle cells were removed developed normally without the test cells until the early tailbud stage. A number of round-shaped cells morphologically similar to the test cells but with different lectin affinities and autofluorescence, then appeared on the neck region(More)
Molecular mechanisms underlying the metamorphosis of larvae, e.g., ligand and receptor interaction, have to be determined and roles for the nervous system in marine invertebrates are not well understood. We report here that treatment of swimming larvae of the ascidian Ciona savignyi with noradrenaline or adrenaline promoted morphological changes in early(More)
In the ascidian Ciona intestinalis (and C. savignyi), sperm-activating and -attracting factor (SAAF) is released from the egg at fertilization and stimulates both Ca(2+) influx and a transient increase in cAMP level of the sperm, leading to the activation of sperm motility (M. Yoshida et al., 1994, Dev. Growth Differ. 36, 589-595). In this paper we show in(More)
In salmonid fishes, rainbow trout and masu salmon, and the plecoglossid fish, ayu, seminal plasma had an osmolality around 300 mosmol kg-1 isotonic to the blood plasma, and contained a higher concentration of potassium than the blood plasma. Spermatozoa of salmonid fishes were motile when semen was diluted 1:100 with solutions of sodium chloride or(More)
Oocytes of the marine bivalve Mactra chinensis are spawned and arrested at the germinal vesicle stage (first meiotic prophase) until fertilization, without undergoing a process called oocyte maturation. As is the case of other animals, a fertilized oocyte of the bivalve displays increases in intracellular free Ca(2+). We have clarified here the(More)
Intracellular Ca2+ transients occur at fertilization in the eggs of all animal species and are thought to be critical for the initiation of several events in egg activation. The rho family of small GTPases are known to organize and maintain the actin filament-dependent cytoskeleton, and rho is involved in the control mechanism of cytokinesis. In the(More)