Genetic basis of cone opsin gene expression

University Of New Hampshire, Durham NH

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Abstract

DESCRIPTION (provided by applicant): Opsin proteins are critical components of visual pigments and determine which wavelengths of light are detected by photoreceptors. Defective opsin genes lead to a variety of retinal diseases including retinitis pigmentosa, congenital night blindness, and color blindness. An understanding of opsin gene expression would contribute to unraveling the mechanisms of neural cell development, differentiation, and patterning. In addition, knowledge of opsin promoters could be important for retinal gene therapy. The goal of this work is to utilize cichlid fishes as a new model for identifying trans acting factors and cis regulatory elements important in controlling cone opsin gene expression. Cichlids have five classes of cone opsin genes, but typically express only three genes. Species vary in the developmental pattern and the combination of genes expressed in adults. Species, differing in expression, are closely related and can be considered naturally occurring mutants which are easy to cross and genetically analyze. In this project we will focus on three cichlid species which have different cone opsin expression patterns. The riverine species, Oreochromis niloticus, expresses each of the five genes at some point during its development. This is the ancestral expression pattern. In contrast, the Lake Malawi species, Copadichromis eucinostomus, expresses only the SWS1, RH2, and LWS genes, while its close relative, Dimidiochromis compressiceps, expresses only the SWS2a, RH2, and LWS genes. Our goal is to identify factors controlling the switch from SWS1 to SWS2a expression. The first aim of the project is to determine which cone opsin genes are expressed in each cone cell type in each species using in situ hybridization. The second aim is to use phylogenetic footprinting to identify cis regulatory elements which are shared between genes expressed in the same cone type. The third aim is to genetically map the trans acting factors which contribute to the SWS1-SWS2a difference in cone opsin expression in a cross of C. eucinostomus x D. compressiceps.