| Co-Investigator(Kenkyū-buntansha) |
HISATOMI Osamu Osaka University, Department of Earth and Space Science, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (60231544)
IWAMURO Shawichi Toho University, Faculty of Science, Lecturer, 理学部, 講師 (70221794)
SUGIMOTO Masazumi Toho University, Faculty of Science, Associate Professor, 理学部, 助教授 (20235899)
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| Research Abstract |
Results obtained for 3 years (1999-2001) are summarized as follows :
1) Erythrophores present in fins of Nile tilapia respond to light. In spectral regions of 400-400 nm and 550-600 nm, pigment aggregation occurs, while dispersion is accelerated at wavelengths between 470 and 530 nm. The degree of such responses depends on the light intensity. The same responses are observed in cultured erythrophores, suggesting the direct action of light on these cells.
2) We examined the expression of mRNA of visual pigments in fins only where erythrophores are present. The PCR primers were designed corresponding to the sequences of tilapia cone opsins (GenBank). RT-PCR demonstrated the expression of mRNAs of two opsins, red opsin and green opsin. Using these cDNA fragments as probes, screening of tail fin cDAN library was performed, and total sequences of the opsins were determined. With in situ hybridization using cRNA of red opsin as probe, the distribution of red opsin mRNA was investigated and the probe was recognized in erythrophores. However, further study is required.
3) Using pertussis toxin, cholera toxin and other chemicals, we found that pigment aggregation or dispersion in response to light are mediated through Gi or Gs, respectively, leading to a decrease or an increase in intracellular cAMP level, respectively. Although we examined the expression of Gt mRNA in tilapia fins, such expression was not detected.
4) In iridophores of the neon tetra, the minimum effective intensity of light is about 3.4 lx. Light with a peak, wavelength of 550 nm is more effective in inducing the photoresponse (a shift in the spectral peak of reflected light to longer wavelengths) compared with light at 500 or 600 nm. Light at 400 nm is less effective.
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