Figure 5.

Pigment dispersion is a common, but not universal, feature of mouse strains with mutations related to Tyrp1. Comparisons of coat color (left column) and ocular phenotypes (right columns). (A) The light allele in LT/SvEiJ mice results in the production of hair that is pigmented at the tip, but very lightly or not pigmented along the hair shaft. As a consequence, coat color is rapidly lightened as hair lengthens. (B) Pigment dispersion was commonly present in the eyes of aged light mice. (C) Higher magnification image of same pupil shown in panel B. Several clumps of dispersed pigment are clearly visible in the pupil (one prominent example indicated with arrowhead, several other unmarked also visible). (D) The vitiligo allele results in a coat that is initially lighter than normal, with extensive white spotting (front mouse). With increasing age, the coat becomes progressively whiter due to increasing numbers of white hairs with each molt (back mouse). (E) Pigment dispersion was striking in eyes of aged vitiligo mice, as shown here in the pupil (arrowhead), across the surface of the iris (open white arrow), and in a pronounced pool accumulated inferiorly (dark band marked by solid black arrow). (F) Eyes of several vitiligo mice became severely enlarged, as sometimes occurs in mice with glaucoma. (G) The silver allele results in a mix of normal and hypopigmented hairs, which together cause a characteristic silvering of the coat. Heterozygosity for Tyrp1^b enhances the silver coat color phenotype as shown here among three young silver homozygotes with differing Tyrp1 genotypes (Tyrp1^+/+ front, Tyrp1^b/b left, and Tyrp1^b/+ right). (H) Mice heterozygous for Tyrp1^b and homozygous for Si^si maintain healthy irides lacking pigment dispersion. (I) Mice homozygous for both Tyrp1^b and Si^si exhibit a characteristic Tyrp1 mutant iris phenotype characterized by iris atrophy and pigment dispersion. Neither the onset nor severity of these Tyrp1^b mediated phenotypes were influenced by Si. Note, because of the unique photographic flash settings used to capture the pigment accumulation near the highly reflective sclera in panel E, the apparent color of this iris is not directly comparable to the images in other panels.