Forward Genetic Studies of Mouse Mutants with Retinal Diseases

Abstract

Abstract: : Purpose:To identify novel genes that play essential role(s) in diseases and development of the retina. Moreover, to elucidate the mechanisms for how these genes mutations lead to retinal defects. Methods: A forward genetic approach: ENU-induced mouse mutants in C57BL/6J strain were screened for ocular phenotypes by clinical examinations using an indirect ophthalmoscope and a slit lamp. Identified phenotypic mutants were verified for genetic inheritance in corresponding to their clinical symptoms. Defined genetic mutants were subjected to chromosomal mapping of their mutations using a genome wide mapping strategy. Their ocular phenotypes were further characterized morphologically and biochemically. Results: Dozens of different ocular mutants have been found from the screen of more than 3000 F1 (for dominant phenotype) and 5000 F3 mice (for recessive phenotype). At least two dominant and two recessive retinal mutations have been identified. a.) A hyper-pigmentation was observed in heterozygous retinal mutant 2 (R2) at the age of 3 weeks. The phenotype was exaggerated as mouse aging. Histological sections showed an alteration of retinal pigment epithelium (RPE) without obvious degeneration of photoreceptor cells of 3-month-old mice (the oldest mice examined so far). The mutation was mapped on chromosome 5. Homozygous R2 is likely to be embryonic lethal. b.) Heterozygous retinal mutation 3 (R3) showed typical retinal degeneration (RD) symptoms: vessel attenuation and optic atrophy. Histological sections verified a loss of most of the outer nuclear layer in 3-week-old mice. Homozygous R3 mutant is likely to be lethal too. c.) r18 mutant developed a recessive RD phenotype. Apoptotic nuclei were detected in the outer nuclear layer of the homozygous mutants e at the adult age. Heterozygous r18 mice have relative normal retina. d.) Homozygous r15 mutants showed RD phenotype according to Fundus examination. Their heterozygous mutants have relative normal retina. Conclusion: These retinal mutants are valuable genetic resource for studying the genes that play important role(s) in the function of the RPE and photoreceptor cells as well as for elucidating the genetic and molecular bases for different retina diseases. The preliminary results of these four novel mutants showed distinctive clinical symptoms and different cellular defects in photoreceptor cells or in pigment epithelium. Further investigation of these four mutants will lead to identify specific genes mutations that cause the phenotypes, and to understand some of the mechanism(s) for the retinal defects.

Keywords: retina • retinal degenerations: hereditary • retinal pigment epithelium