ID 21578
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Developing oocytes arrest at the prophase of meiosis I, while the hormone progesterone restarts the process, leading to full maturation as fertile eggs. In this study we investigated the effects of hypergravity on this phase of maturation using oocytes of Xenopus. No differences were found between 2G and 5G treated groups and untreated controls regarding time to resumption of maturation, as judged by the appearance of a white spot in the animal hemisphere. However the white spot itself was larger and brighter in treated oocytes at time of appearance, and became even more pronounced as maturation proceeded. These findings suggest that although hypergravity does not affect the resumption of maturation, it might adversely affect the subsequent process and the final results.

Because there is mounting evidence to suggest that oxidative stress is involved in the pathophysiology of albinism, albino amphibians are useful tools for studies on imbalances in the oxidant-antioxidant system. In the course of maintaining albino mutant frog strains it was found that crosses between albino males and heterozygous females of Rana nigromaculata sometimes produce offspring displaying pigmentary mosaicism. After hatching hypopigmented portions appear on the left or right side of the body, and this is accompanied by such abnormalities as poor viability, asymmetrical curvature of the body toward the hypopigmented side, and limb deformity. Histological examination of mosaics showed the cells of various tissues (except kidney) to be smaller on the hypopigmented side and larger on the pigmented side compared to corresponding cells in wild type offspring. Cytogenetic analysis of cultured skin cells revealed that wild type and albino individuals were diploidal with 26 chromosomes, the same as normal R. nigromaculata. In mosaics on the other hand, cells of hypopigmented portions were almost exclusively haploidal with 13 chromosomes, while pigmented portions were a mixture of roughly 75% triploidal, 39 chromosome cells and roughly 25% haploidal, 13 chromosome cells.
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Effects of hypergravity on oocyte maturation in Xenopus laevis. Ichiro Tazawa, Akihiko Kashiwagi, Keiko Kashiwagi, and Nobuaki Furuno. Biol. Sci. Space, 19 (4) (2005) 242-244.
Skin pigmentary variants in Rana nigromaculata. Ichiro Tazawa, Hitoshi Okumoto, and Akihiko Kashiwagi. J. Clin. Biochem. Nutr., 38 (3) (2006) 195-203.
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広島大学(Hiroshima University)
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Physical Science
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Graduate School of Science