Two distinct phenotypes in pigmented cells of different embryonic origins in eyes of pale ear mice

•Pigmentation in whole eyes of the pale ear mutant was delayed and reduced.•Tyrosinase activity in eyes of the pale ear mouse increased gradually after P7.•Two distinct phenotypes in pigmented cells were due to one single mutation of HPS-1.•Macromelanosomes were absent in iris stroma of pale ear mouse at early stages.•Lipofuscin accumulated massively in the RPE of the pale ear mouse.

The eye has pigmented cells of two different embryonic origins and therefore it is a good model for studying melanosome biogenesis and melanin production/deposition. Pale ear mice bear a mutation in the Hermansky–Pudlak syndrome type 1 (HPS-1) gene and exhibit abnormal eye pigmentation. Here, we reported the delayed and reduced pigmentation in eyes of pale ear mice in early postnatal stages and adulthood. Tyrosinase assay and l-3,4-dihydroxyphenylalanine (l-DOPA) gel staining assay revealed that tyrosinase activity in eyes of pale ear mutants was greatly reduced in early postnatal stages and increased gradually after postnatal day 7 (P7). Further histological examination revealed that hypopigmentation in the retinal pigment epithelium (RPE) and pigment epithelium of the iris and ciliary body, which are derived from the optic cup, was more severe than that in neural crest-derived tissues. In addition, macromelanosomes were exclusively present in neural crest-derived melanocytes of pale ear adults, but absent at early postnatal stages. Taken together, the mutation in the HPS-1 gene could cause two distinct phenotypes in pigmented cells of different embryonic origins. Besides, an increased accumulation of lipofuscin in RPE was also observed.