| Research Abstract |
In this research, functional differentiation and maintenance of morphology of photoreceptor cells, the major cells of compound eyes, were studied. First, the photoreceptor structure and its abnormality by the deficiency of photopigments were analyzed by rapid freezing fixation with liquid helium, arresting the retina under the condition closest to its living state. By this method, the photopigments were revealed to be arranged in spiral, correlating with the characteristics of photosensitivity. Second, the proteins involved in phosphatidylinositol turnover were studied as for their localization and its abnormality in mutants. The results showed that diacylglycerol kinase (rdgA protein), CDP-diacylglycerol synthase (CDS) and phosphatidylinositol transfer protein (rdgB protein) localize to the subrhabdomeric cisternae (SRC), a smooth endoplasmic reticulum adjacent to the photoreceptive site. The SRC in the mutants of these proteins collapse causing the photoreceptor cell degeneration. SRC are known to the inositol trisphosphate sensitive calcium pool. This, together with our data, indicates that phototransduction cascade mediated by inositol trisphosphate and phosphatidylinositol regeneration cycle are localized to the same subcellular structure, which guarantee the continuous readiness of phototransduction. Such localization of molecules are likely to apply to other systems as well. For example, protein aggregation in signaling cascade by adaptor proteins or by cytoskeletal elements are reported. Thus, the significance of the topology of molecules constituting a functional unit will certainly draw intense attention hereafter. Drosophila, in which molecular biology is easily applied, will be an excellent model for such investigations.
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