International Mammalian Genome Society

The 14th International Mouse Genome Conference (2000)

B27. Two Interacting Genes, rct and mrct, Regulating New Recessive Cataract in the Mouse

Yukiko Y. Maeda1, Nobuaki Funata2, Sumiyo Takahama1, Yasuo Sugata3 and Hiromichi Yonekawa1
The Tokyo Metropolitan Institute of Medical Science, 1Dept . of Laboratory Animal Science, Tokyo Metropolitan Komagome Hospital, 2Dept. of Pathology, 3Dept. of Ophthalmology.

As a new mouse model for human hereditary cataract, we discovered a spontaneous mutant, RCT (Rinshoken cataract), in our institute. RCT mice develop congenital and bilateral cataract and was also associated with microphthalmia. Opacity of lens could be visually observed at the age of approximately 14 week-old RCT mice, due to slow development of the cataract. However, initial changes in lens could be observed at 2 days after birth by histological analyses. The major symptoms are the loss of fine structure on the lens fibers, marked swelling of the epithelial cells with many vacuoles in various sizes in the cortex of lens. The chromosomal location of the responsible gene was determined by the histological analyses of the phenotype and interval mapping using 265 heads of backcross (N2) segregates between RCT and MSM/Ms, an inbred strain from Japanese wild type Mus musculus molossinus. As the result, phenotypes of N2 segregates were divided into three groups, (1) early onset cataract, which can be detected visually as well as that of RCT mice. (2) late onset cataract, which can detected histologically but not visually. (3) normal lens, in which any histological changes can not be detected. Their ratio was approximately 1: 1: 2, indicating that two major genes, rct and mrct (a modifier of rct), regulate the onset of RCT cataract. The rct locus was located at D4Mit278 with no recombinant. N2 segregates showing cataract, early or late onset, were exclusively homozygous at D4Mit278, indicating that rct is essential for the onset of the cataract. The mrct locus was located close to D5Mit239 (2=66.3, P<<0.00001). Early onset segregates showed homozygous at D5Mit239, but not late onset did.

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