title: Homeobox transcription factor Six7 governs expression of green opsin genes in zebrafish.
abstract: Colour discrimination in vertebrates requires cone photoreceptor cells in the retina, and high-acuity colour vision is endowed by a set of four cone subtypes expressing UV-, blue-, green- and red-sensitive opsins. Previous studies identified transcription factors governing cone photoreceptor development in mice, although loss of blue and green opsin genes in the evolution of mammals make it difficult to understand how high-acuity colour vision was organized during evolution and development. Zebrafish (Danio rerio) represents a valuable vertebrate model for studying colour vision as it retains all the four ancestral vertebrate cone subtypes. Here, by RT-qPCR and in situ hybridization analysis, we found that sine oculis homeobox homolog 7 (six7), a transcription factor widely conserved in ray-finned fish, is expressed predominantly in the cone photoreceptors in zebrafish at both the larval and the adult stages. TAL effector nuclease-based six7 knock-out revealed its roles in expression of green, red and blue cone opsin genes. Most prominently, the six7 deficiency caused a loss of expression of all the green opsins at both the larval and adult stages. six7 is indispensable for the development and/or maintenance of the green cones.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Yohey
authors.identifier: http://orcid.org/0000-0001-9031-4393
authors.initials: Y
authors.lastname: Ogawa
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Tomoya
authors.identifier: http://orcid.org/0000-0003-0447-007X
authors.initials: T
authors.lastname: Shiraki
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Daisuke
authors.identifier: http://orcid.org/0000-0003-2658-780X
authors.initials: D
authors.lastname: Kojima
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan sfukada@mail.ecc.u-tokyo.ac.jp.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Fukada
mesh_terms: D000818:Animals; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D017403:In Situ Hybridization; D060888:Real-Time Polymerase Chain Reaction; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D017299:Rod Opsins / Q000235:genetics* / Q000378:metabolism; D015027:Zebrafish / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029961:Zebrafish Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D018398:Homeodomain Proteins; D017299:Rod Opsins; C114547:Six7 protein, zebrafish; D029961:Zebrafish Proteins
keywords: cone opsin; green opsin; photoreceptor development; six7; zebrafish (Danio rerio)