International Mammalian Genome Society


The 13th International Mouse Genome Conference
October 31-November 3, 1999

Table of Contents * Structure * Bioinformatics * Sequence * Mapping * New Tools * Gene Discovery * Developmental * Mutagenesis * Functional Genomics

E14 QTLs Associated with Protection of Mouse Photoreceptors from Light-Induced Damage; An Rpe65 Variant is Associated with One of Them

M Danciger1,2, MT Matthes3, D Yasumura3, NB Akhmedov1, M Redmond4, S Gentleman4, MM LaVail3, DB Farber1. 1Jules Stein Eye Institute, UCLA; 2Loyola Marymount University, Los Angeles; 3University of California, San Francisco; 4NEI, NIH

When C57BL/6J-c2J (c2J) albino mice were exposed to constant light for several weeks they suffered much less photoreceptor damage than BALB/c mice. Preliminary data revealed that the difference in response to light (not influenced by gender) was a complex trait. By analysis of a backcross between c2J and BALB/c mice 2 QTLs were identified: one on Chr 3 and the other on Chr 14. The Rpe65 gene which maps within the Chr 3 QTL was studied in the two mouse strains.Progeny mice (194) from the backcross (c2J x BALB/c)F1 x c2J were kept in constant light for 2 weeks. After this time their retinas were scored for outer nuclear layer (ONL) thickness; the ONL is where the cell bodies of the photoreceptor cells lay intercalated at about 10 nuclei (~ 45 mm) thick. The ONL thickness quantitative trait was compared to the genotypes of a set of 118 dinucleotide repeat markers spanning the genome. Analysis with Map Manager QT revealed QTLís on Chrs 3 and 14. The Rpe65 candidate gene present in the Chr 3 QTL was tested for linkage with a trinucleotide repeat present in one of its introns. Rpe65 mRNA was amplified by RT-PCR and subcloned, and its genomic DNA amplified directly. All sequencing was performed with an automated fluorescent sequencer. Analysis of the Rpe65 genotype showed the gene to give the most highly significant likelihood ratio in the Chr 3 QTL. Sequence analysis of the 5 UTR, the coding region and the 3 UTR of c2J and BALB/c cDNAs corresponding to Rpe65 revealed a single base difference at codon 450; in c2J it was ATG (MET) and in BALB/c it was CTG (LEU). No difference was found between the strains in expression of Rpe65 mRNA in Northerns, nor in 983 bp upstream of the transcription start site sequenced from genomic DNAs. Sequencing of the region containing codon 450 in genomic DNAs showed CTG (LEU) to be present in each of four other mouse strains that are sensitive to light like BALB/c. All other animals for which RPE65 sequence was available (human, dog, rat, cow, tiger salamander and chicken) also had LEU450.

Light exposure is known to exacerbate some inherited retinal degenerations in mice, and thought to contribute to some inherited retinal degenerations as well as to age-related macular degeneration (AMD) in humans. Variants like 450MET of Rpe65 which is associated with protection from light-induced damage in the mouse retina may influence the course of light-sensitive retinal degenerations in humans.

 


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