Masaaki Morisawa

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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)
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 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)
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)
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)
Ca2+-influx and membrane hyperpolarization by sperm-activating and -attracting factor (SAAF) released from the unfertilized egg of the ascidians Ciona cause a transient increase in cAMP, which triggers activation of sperm motility. We demonstrated here the presence of Ca2+-binding protein, calmodulin (CaM), and CaM-dependent kinase II (CaMKII) in the sperm.(More)
The formation of an acrosomal process at acrosomal exocytosis in spermatozoa of the amphioxus was described in the present report for the first time. A non-reacted acrosome was located in front of the nucleus, where a cup-shaped acrosomal vesicle covered a conical accumulation of subacrosomal material. When naturally spawned spermatozoa were treated with a(More)
Morphological changes in the tunic layers and migration of the test cells during swimming period in the larva of the ascidian, Ciona intestinalis, were observed by light and electron microscopy. The swimming period was divided into three stages. In stage 1, further formation of juvenile tunic layer started only in the larval trunk and neck region. In stage(More)
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