無尾両生類を用いた発生異常の研究

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.広島大学(Hiroshima University)博士(理学)Physical Sciencedoctora

A novel Xenopus laevis larval keratin gene, xlk2 : its gene structure and expression during regeneration and metamorphosis of limb and tail

A novel cytokeratin (CK) gene, xlk2, was cloned from a cDNA library prepared from regenerating limbs of Xenopus larvae. The deduced amino acid sequence indicated that its product, XLK2, is a 48 kDa type I (acidic) CK and has a high similarity to CK13, 15, and 19 with the highest homology (58%) to mouse CK15. The gene of xlk2 exclusively expressed in basal cells of the bi-layered larval epidermis, but not in other cells in larvae and not in other periods of life. Its expression was down-regulated during spontaneous and thyroid hormone-induced metamorphosis. The basal cells of the apical epidermal cap (AEC) formed on the regenerate of larval limbs terminated the expression of xlk2, whereas those of the adjacent normal epidermis continued to express it. The AEC-basal cells did not re-express the gene in the regenerate. In contrast, the basal cells of the tail regenerate also once terminated the expression of xlk2, but was able to re-express xlk2 later, supporting a notion that the "de-differentiated" basal cells of the tail epidermal regenerate re-differentiate into larval normal epidermal cells