Characterization of mouse melanocytes reveals ultrastructural and immunological insights into the inner ear function.

Melanocytes are important components of the inner-ear cellular architecture. However, limited morphological research hinders our understanding of inner-ear function. Here, we characterize the morphology of inner-ear melanocytes and cells often misidentified as melanocytes. Immunofluorescence, smart-seq, transmission/field emission scanning electron microscopy, and immunoelectron microscopy are used. Cells previously referred to as "perivascular macrophage-like melanocytes" are not observed in the stria vascularis and are actually macrophages; along with melanocytes, they constitute intermediate cells. Cells with a "black ball" appearance in the vestibule are identified as macrophages. We examine variation in melanocytes or macrophages with age, strain, and cisplatin injury. Kir4.1 expression and the greater noise resistance observed in pigmented mice suggest melanocyte functions. Based on melanin distribution in Pou3f4(y/-) mice, we hypothesize that melanocytes migrate from the modiolus along Reissner's membrane area to the stria vascularis, following a base-to-apex gradient. These findings provide novel ultrastructural and immunological insights into inner-ear function.