MAPPING AND RETINAL PHENOTYPE OF THE HUGGER MUTATION IN THE MOUSE

Hugger, hug, is a recessively expressed mutation in mice that features mildly abnormal locomotion, not yet explained, and a unique combinati on of developmental and degenerative retinal abnormalities. Analysis w ith the efficient MEV linkage testing stock established that hug is on mouse Chr 19 about 14 cM from th centromere, between the microsatelli te markers D19Mit28 and D19Mit24. An abnormal retinal phenotype was re cognized on the day of birth, when some retinal ganglion cells already lie in abnormal positions in the inner plexiform layer. By postnatal day 18 the number of neurons is reduced in all three cellular layers o f the retina. Rod photoreceptor cells develop only rudimentory outer s egments, and by 9 months of age, about 75% of the photoreceptor cells have completely disappeared. Similar photoreceptor cell abnormalities are seen in prph2 (formerly rds) homozygotes, which lack the peripheri n/rds protein of the rod outer segments, but a mating of the respectiv e homozygotes yielded normal progeny. Rom1, which codes for an outer s egment protein similar to peripherin/rds, maps to a more proximal posi tion on Chr 19.