Analyses of direct action of light on fish chromatophores

1999-2001年3年的研究结果总结如下：1)尼罗罗非鱼鱼鳍中的红细胞对光有响应。在400-400 nm和550-600 nm的光谱区域，色素发生聚集，而在470 - 530 nm之间的波长加速色散。这种反应的程度取决于光的强度。在培养的红细胞中观察到同样的反应，表明光对这些细胞的直接作用。2)我们只在红细胞存在的鳍中检测了视觉色素mRNA的表达。根据罗非鱼锥视蛋白序列（GenBank）设计PCR引物。RT-PCR检测到红视蛋白和绿视蛋白两种视蛋白的mrna表达。以这些cDNA片段为探针，筛选鱼尾cDAN文库，测定视蛋白总序列。以红视蛋白的cRNA为探针进行原位杂交，研究了红视蛋白mRNA的分布，并在红细胞中识别了探针。然而，还需要进一步的研究。3)利用百日咳毒素、霍乱毒素等化学物质，分别通过Gi或Gs介导色素对光的聚集或分散，分别导致细胞内cAMP水平的降低或升高。虽然我们检测了罗非鱼鱼鳍中Gt mRNA的表达，但没有检测到这种表达。4)在虹膜中，最小有效光强约为3.4 lx。与500或600纳米的光相比，波长为550纳米的光在诱导光响应（反射光的光谱峰向更长的波长移动）方面更有效。400纳米的光效果较差。

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.