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Zebrafish have two red, LWS-1 and LWS-2, and four green, RH2-1, RH2-2, RH2-3 and RH2-4, opsin genes encoding photopigments with distinct absorption spectra. Occurrence of opsin subtypes by gene duplication is characteristic of fish but little is known whether the subtypes are expressed differently in the retina, either spatially or temporally. Here we show by in situ hybridization the dynamic expression patterns of the opsin subtypes in the zebrafish retina. Expression of red type opsins is initiated with the shorter-wavelength subtype LWS-2, followed by the longer-wavelength subtype LWS-1. In the adult retina, LWS-2 was expressed in the central to dorsal area and LWS-1 in the ventral and peripheral areas. Expression patterns of green type opsins were similar to those of the red type opsins. The expression started with the shortest wavelength subtype RH2-1 followed by the longer wavelength ones, and in the adult retina, the shorter wavelength subtypes (RH2-1 and RH2-2) were expressed in the central to dorsal area and longer wavelength subtypes (RH2-3 and RH2-4) in the ventral and peripheral areas. These results provide the framework for subsequent studies of opsin gene regulation and for probing functional rationale of the developmental changes by using the power of zebrafish genetics.
Takechi et al. (Mon,) studied this question.