Phosphoinositide metabolism in Drosophila phototransduction: A coffee break discussion leads to 30 years of history

The aim of this review is to summarize the history of Dr. Yoshiki Hotta and his collaborators' contributions to the research field of Drosophila phototransduction. The electroretinogram-defective mutants reported in 1970 by Dr. Hotta and Dr. Seymour Benzer in the article entitled "Genetic dissection of the Drosophila nervous system by means of mosaics" have attracted the interest of many researchers, and have been used as a great tool to dissect the mechanisms underlying phototransduction. The early collaboration of Dr. Hotta with the group of Dr. Tohru Yoshioka, who was studying the roles of phosphoinositides in the nervous system biochemically, combined biochemical and genetic approaches to phototransduction-defective no receptor potential A (norpA) and retinal degeneration A (rdgA) mutants, which led to the hypothesis that phosphoinositide metabolism regulates phototransduction in Drosophila. This was proven later by the identification of the norpA and rdgA mutant genes, which encode phospholipase C and diacylglycerol kinase, respectively. Thus the collaboration of Dr. Hotta and Dr. Yoshioka laid the foundation of our understanding of the role of phosphoinositide metabolism in Drosophila phototransduction. In addition, a collaboration carried out with the group of Dr. Kazushige Hirosawa on the ultrastructural analyses of retinal degeneration mutants, rdgA and rdgB, led to the discovery of the subcellular membrane organelle called submicrovillar cisternae, which is involved in the phosphoinositide metabolism. In this review, the authors will summarize these results, which were inspired by Dr. Hotta's insights.