X-ray hypersensitivity in the LEA rat: genetic linkage analysis of responsible loci

d-Amino acid oxidase deficiency is caused by a large deletion in the Dao gene in LEA rats

d-Amino acids, enantiomers of l-amino acids, are increasingly recognized as physiologically active molecules as well as potential biomarkers for diseases. d-Amino acid oxidase (DAO) catalyzes the oxidative deamination of d-amino acids and is present in a wide variety of organisms from yeasts to humans. Previous studies indicated that LEA rats lacked DAO activity, and levels of d-Ser and d-Ala were markedly increased in their tissues, suggesting a mutated locus responsible for the lack of Dao activity (ldao) existed in the LEA genome. Sequence analysis identified deletion breakpoints located in intron 4-5 of the Dao gene and intron 1-2 of the Svop gene, resulting in a 54.1-kb deletion which encompassed exons 5-12 of the Dao gene and exons 2-16 of the Svop gene. We developed a novel congenic rat strain, F344-Dao^ldao, harboring the Dao^ldao mutation from LEA rats delivered onto the F344 genetic background. Compared to the parental F344 strain, in F344-Dao^ldao rats d-Ala was markedly increased in both cerebrum and cerebellum, while d-Ser content was increased in cerebellum but not cerebrum. d-Ala, d-Ser, d-Pro and d-Leu levels were also elevated in F344-Dao^ldao plasma. F344-Dao^ldao rats represent a novel model system that will aid in elucidating the physiological functions of d-amino acids in vivo. (203 words).

A deletion in the Ctns gene causes renal tubular dysfunction and cystine accumulation in LEA/Tohm rats

The Long-Evans Agouti (LEA/Tohm) rat has recently been established as a new rat model of type 2 diabetes. The onset of diabetes mellitus was observed only in male LEA/Tohm rats; however, urinary glucose appeared before the onset of diabetes. To clarify the genetic basis of urinary glucose, we performed genetic linkage analysis using (BN × LEA) F₂ intercross progeny. A recessively acting locus responsible for urinary glucose excretion (ugl) was mapped to a 7.9 Mb region of chromosome 10, which contains the cystinosin (Ctns) gene. The Ctns gene encodes the cystine transporter, which transports cystine out of the lysosome and is responsible for nephropathic cystinosis in humans. Sequence analysis identified a 13-bp deletion in the Ctns gene, leading to a truncated and loss-of-function protein, which cause cystine accumulation in various tissues. We also developed a novel congenic rat strain harboring the Ctns^ugl mutation on the F344 genetic background. Phenotypic analysis of F344-Ctns^ugl rats indicated that the incidence of urinary glucose was 100% in both males and females at around 40 weeks of age, and marked cystine accumulation was observed in the tissues, as well as remarkable renal lesions and cystine crystals in the lysosomes of the renal cortex. Furthermore, treatment with cysteamine depleted the cystine contents in F344-Ctns^ugl rat embryonic fibroblasts. These results indicated that the F344-Ctns^ugl rat provides a novel rat model of cystinosis, which allows not only a better understanding of the pathogenesis and pathophysiology of cystinosis but will also contribute to the development of new therapies.