| Research Abstract |
The blue damselfish, Chrysiptera cyanea, is a representative tropical fish noted for its beautiful cobalt-blue coloration. It rapidly becomes dark violet (excitement darkening) and sometimes becomes yellowish green (excitement blanching) when it is put under various stresses. In the skin of this fish, simple dermal chromatophore units consisting only iridophores and melanophores were observed. forming a compact single layer, the iridophores lie just under the subepidermal collagenous lamella, and melanophores underlie the iridophore layer. Our electron-microscopic observations indicated that a nucleus is positioned near the top of the cytoplasm of the cell and from it a number of piles of the light-reflecting platelets dispose radially.
Using split-fin preparations, analyses were made on the mechanisms of light reflectivity in the iridophores, which have also been disclosed to be motile, being regulated by the sympathetic nervous system. A rather steep spectral peak of the reflected lig
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ht is apparently due to the multilayered thin-film interference phenomenon of the "non-ideal" type. If a skin specimen was equilibrated in the physiological saline, the spectral peak of light stood around 380 nm, but could be shifted towards longer wavelength up to 530 nm by adrenergic stimuli. Reverse changes were aroused by the effect of adenosine, which has late been shown to be the co-transmitter of chromatic fibers. A hypotonicity of the bathing media also gave rise to a shift of the wave-band up to about 600 nm. These observations indicate that the shift of the peak towards longer or shorter wavelengths may be due to the simultaneous increase or decrease in the distance between adjoining platelets within a stack of them.
All antimitotic reagents tested, i.e. colchicine, vinblastine and podophyllotoxin, inhibted the "coloring response", in which the cells become reflective to light rays of longer wavelength. An actin inhibitor, cytochalasin B, however, did not. EHNA, a dynein ATPase inhibitor, also blocked the iridophore response effectively. These results indicate that the tubulin-dynein system may be involved in the motility of iridophores. For further analysis, the disposition of microtubules inside the cell must be described in detail at the fine structural level, with special attention being paid to the relationship of the tubules to the platelets. The use of specific antiserum aginst tubulin might be useful in elucidating the distribution of the protein within the cytoplasm. Less
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