Morphological and genetic characteristics of the open-eyelid mutant spontaneously occurring in NC-strain mice

A heritable open-eyelid mutant which arose spontaneously in the NC strain of mouse in 1982 has been maintained as the NC-eob line through brother-sister matings. When the line exceeded the 12th generation, its reproductive capabilities were initially compared with those of the NC strain. Then eye abnormalities were investigated morphologically and genetically. Although most of the reproductive parameters in the NC-eob line were comparable to those in the NC strain, a significant decrease was observed in the mean number of pups delivered, and the viability of pups at 7 days of age was reduced to 55%. The eyelids of pups were widely open at birth. The exposed cornea dried within a few hours and a bloody exudate appeared around the margin of the eyelids. At 1 day of age, the eye opening was smaller in size and covered with a scab. Histological examination demonstrated apparent inflammatory changes in the cornea and conjunctiva. At 21 days of age, the eyes revealed opacity, a rough surface, and microphthalmia. Histological findings in the cornea, such as keratosis and vascularization, coincided with the eye opacity. The weight and size of the eyeballs were almost the same as those in normal NC pups. However, a significant decrease in the length of the palpebral rima was evident and this was considered to be the cause of the microphthalmia. The results of genetic analysis indicated that these eye abnormalities were caused by an autosomal recessive gene, eob. These results suggested that the eob gene might be a new mutation manifesting semi-lethality as a pleiotropic effect.