| Research Abstract |
The ultimate goal of this study is to nuderstand how animals process sensory information in the brain. The specific aims are to reveal (1) the distribution pattern of five different types of spectral receptors in the ommatidial retinula of a butterfly Papilio xuthus electrophysiologically, (2) the projection pattern of these receptors in the visual center anatomically, (3) the primary structures of visual pigment molecules by cloning visual pigment-encoding mRNAs, and (4) the distribution pattern of the photoreceptors that express the cloned mRNAs by in situ hybridization.
An ommatidium has nine photoreceptors (R1-9). R1-4 bear microvilli in the distal half of the ommatidium, whereas R5-8 have microvilli in the proximal half forming a rhabdom. R9 contributes to the rhabdom only at the base. By electrophysiology, we revealed that R1 and R2 are either UV,violet, or blue receptors, whereas R3 and R4 are all green type. R5-9 appeared to be green or red receptors.
We then cloned three visual
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pigment-encoding mRNAs (Rh1-3. All consist of 379 amino acids, 72% of which are identical. We then carried out in situ hybridization. Probes were hybridized on 10um frozen sections of the retina. Each gave different hybridization pattern. The probe for Rh1 labeled only in the distal layr. The Rh2 probe labeled all ommatidia distally and some proximally. The Rh3 probe labeled some in proximally. The labeling patterns match with the electrophysiologically determined distribution of short-wavelength (UV,violet, or blue), green, and red receptors, respectively.
In the proximal layr, green and red receptors appeared to exist in separate ommatidia. The distribution of the green and red types are rather random. Although the random distribution of different types of ommatidia is perhaps important for color vision, we still don't know its biological signficance. In the course of the present research we found some different phenomena that also indicate the randomness. Color of screening pigment in the photoreceptors and the fluorescence under UV are such examples. By studying the relationship between them, the function of the random organization of the retina will be elucidated. Less
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