Evolution and the origin of vertebrate retinal photoreceptor cells: insights from tunicates and medaka

Evolution and the origin of vertebrate retinal photoreceptor cells: insights from tunicates and medaka

Speaker: Professor Takehiro Kusakabe, Faculty of Science and Engineering & Institute for Integrative Neurobiology, Konan University, Kobe, Japan

Host: Professor Simon M Hughes

Abstract: The vertebrate retina contains two types of photoreceptor cells, rods and cones. Cones can be further divided into four subtypes with differing wavelength sensitivity. Although photoreceptor development has been extensively studied in a variety of vertebrate species, the mechanism by which photoreceptor subtypes are established is still poorly understood. It also remains unclear how vertebrate retinal photoreceptor cells evolved. In the first half of this seminar, I will talk about the development and molecular properties of photoreceptor cells in tunicates. Tunicates are the only invertebrates that have the vertebrate-type opsins, and therefore studies on tunicate photoreceptor cells are of particular interest in the context of the origin of vertebrate retinal photoreceptors. In the second half of my talk, I will focus on photoreceptor-specific miRNAs, which are potentially involved in photoreceptor subtype specification in a vertebrate retina. In the medaka Oryzias latipes, the genes encoding miR-726 and miR-729 are located upstream of the red-sensitive opsin gene and the UV-sensitive opsin gene, respectively, and are co-expressed with the respective opsins in specific cone subtypes. Based on the transcriptomic analysis of the retina of miRNA knockout fish, I will discuss the role of these miRNAs in the development and evolution of retinal photoreceptor cells.