Genetic analysis of cataract in Ihara epileptic rat

Abstract.

We analyzed the mode of inheritance of cataract in the Ihara epileptic rat (IER) by crossing experiments, and mapped cataract-related genes by linkage analysis. Cataract did not develop in the F₁ animals, but it developed in both male and female animals of backcross and F₂. The occurrence rate of cataract was 48.5% in the backcross progeny and 19.4% in the F₂ progeny. Thus, the character was considered to be inherited by the autosomal recessive mode. We found two groups that differed according to the time of onset among the backcross and F₂ progeny: an early-onset group (EOG), in which cataracts developed by about 4 months after birth, and a late-onset group (LOG), in which cataracts developed 8 months or more after birth. Linkage analysis indicated the presence of one cataract gene each on Chromosome (Chr) 8 and Chr 15, and the cataract was demonstrated to be governed by more than one gene. The gene on Chr 8 was named Cati1, and that on Chr 15, Cati2. Cati1 was involved in the occurrence of cataract, and the conditions required for cataract to develop were Cati1 ⁱ/Cati1 ⁱ or Cati1 ⁱ/Cati1 ^w. However, in the cataract rats with Cati1 ⁱ/Cati1 ^w, the allele of Cati2 was always Cati2 ⁱ/Cati2 ⁱ. Cati2 was involved in the timing of onset of the cataract, and the precondition for early onset was Cati2 ⁱ/Cati2 ⁱ.