Yasuhiro Hiramoto

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A large quantity of paraffin oil, sucrose solution, or sea water was injected into the eggs of the heart urchin Clypeaster japonicus shortly before the onset of the first cleavage. The injected oil became spherical, pushing the mitotic apparatus aside. The sucrose solution mixed with the protoplasm and caused disintegration of the mitotic apparatus, and the(More)
1. The responses of starfish sperm flagella to mechanical stimulation with a microneedle were analysed. Flagellar movement was recorded by high-speed microcinematography and by stroboscopic observation. 2. The amplitude of the bending wave of a flagellum was restricted over its entire length when the microneedle was brought near to the flagellum at its(More)
Fluorescently labeled tubulin was quickly incorporated into the mitotic apparatus when injected into a live sand dollar egg. After a rectangular area (1.6 X 16 microns) of the mitotic spindle was photobleached at metaphase or anaphase by the irradiation of a laser microbeam, redistribution of fluorescence was almost complete within 30 sec. The photobleached(More)
A series of periodic increases in intracellular free calcium concentration ([Ca2+]i) occurred upon fertilization in golden hamster eggs. The spatial distribution of the Ca2+ transients was investigated in single zona-free, aequorin-injected eggs, inseminated by single sperm. A supersensitive TV camera system for recording Ca2+-aequorin luminescence enabled(More)
Eggs of Xenopus laevis were preloaded with aequorin and the spatial and temporal pattern of free calcium release in the egg cortex on artificial activation was determined by the aequorin luminescence emitted from the thin cortical layer of naturally opaque eggs. The aequorin luminescence was detected with a photonic microscope system consisting of a light(More)
Electron microscope preparations were made of specimens of Actinosphaerium nucleofilum fixed in glutaraldehyde before, during, and after exposure to high pressures (4,000 to 8,000 psi). A study of this material showed that, although other organelles were relatively stable, the microtubular elements of the axopodia and cytosome became unstable under(More)
The changes in stiffness of the cell before and during cleavage reported previously for various kinds of echinoderm eggs are classified into three types. There is no general rule that cleavage starts when the stiffness attains a maximum or a minimum. Because the stiffness of the cell surface is much greater than that of the mitotic apparatus, the change in(More)