|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1994 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1993 : ¥1,600,000 (Direct Cost : ¥1,600,000)
In order to elucidate the molecular mechanism of rhodopsin synthesis and transport in the Drosophila photoreceptor cells, investigations were carried out with special reference to the following points : (1) importance of molecular conformation of opsin, (2) identification of Drosophila Rab proteteins, and (3) interaction between opsin transport and signal transduction system. The present research then elucidated that : (1) when normal forlding of opsin molecule was prohibited by the amino acid substitution of opsin or chromophore starvation, processing of the glycosylated opsin (immature form of opsin) was inhibited, and opsin bearing large (highmannose) oligosaccharide chain was accumulated. Both in vitro and in vivo experiments indicated that single oligosaccharide chain was attached at the N-terminal region of opsin immediately after translation. The sugar chain was essential to stabilize the immature opsin, but must be processed before forming a functional rhodopsin. (2) Carotenoid deprivation affected the transcription of drosophila Rab genes. In this study, 14 kinds of Rab proteins were identified in the Drosophila retinal. Four of them (including one novel member of Rab) showed carotenoid-depandent mRNA expression. Since the similar regulation of Rab expression with carotenoid was also found in the brain, this regulation may run widely in the nervous system. (3) Retinal degeneration caused by the irradiation with strong light was resulted from the inhibition of opsin synthesis, as well as abnormal invagination of microvillar membrane into cytosol. The inhibition of opsin syntheisi was caused by blocking of opsin transport from rER to microvillar membrane, which was induced by the hyper-activation of phototransduction system. Based upon these results, a rough model for opsin synthesis was constructed.