Development and degeneration of retina in rds mutant mice: altered disc shedding pattern in the heterozygotes and its relation to ocular pigmentation

In the heterozygous mutant (rds/+) mice, receptor outer segments (ROS) are irregular in form and are shed as abnormally large phagosomes. In the albino rds/+ mice, peak frequency of pigment epithelial (RPE) phagosomes is higher than normal and is recorded near the end of the light period, instead of at the time of light onset as in the normal (+/+) albino mice. In pigmented mice of both genotypes, the maximum numbers of phagosomes in the RPE remain lower than in the albinos. In pigmented +/+ mice the number of phagosomes is already high at the time of light onset. The number rises to peak after one hour and then declines slowly. The lowest frequency is reached after the end of the light period. In pigmented rds/+ mice, the number of phagosomes in the RPE is lowest at the time of light onset. The number rises rapidly to peak level within two hours, then declines and remains low until light onset. If the dark period is prolonged, phagosome frequency in the rds/+ RPE remains lower than in +/+ RPE. If the light period is prolonged, phagosome frequency in the rds/+ RPE remains at a higher level than in the +/+ RPE, This differential response to altered light regimen in the rds/+ and +/+ mice is less pronounced in the pigmented than in the albino individuals. The phagosomes in the rds/+ RPE are larger than in the +/+ RPE in all light regimens. These results show that ocular pigmentation may modify the circadian pattern of ROS disc shedding in the rds/+ retina.