Department of Biology, University of Washington, Seattle, United States; Molecular and Cellular Biology Program, University of Washington, Seattle, United States
Molecular and Cellular Biology Program, University of Washington, Seattle, United States; Department of Biological Structure, University of Washington, Seattle, United States
Nathaniel G Yee
Department of Biology, University of Washington, Seattle, United States
Everett T Fan
Department of Biology, University of Washington, Seattle, United States
Department of Biological Structure, University of Washington, Seattle, United States; Department of Otolaryngology - Head and Neck Surgery, University of Washington, Seattle, United States; Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, United States
Department of Biology, University of Washington, Seattle, United States; Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, United States
Touch system function requires precise interactions between specialized skin cells and somatosensory axons, as exemplified by the vertebrate mechanosensory Merkel cell-neurite complex. Development and patterning of Merkel cells and associated neurites during skin organogenesis remain poorly understood, partly due to the in utero development of mammalian embryos. Here, we discover Merkel cells in the zebrafish epidermis and identify Atonal homolog 1a (Atoh1a) as a marker of zebrafish Merkel cells. We show that zebrafish Merkel cells derive from basal keratinocytes, express neurosecretory and mechanosensory machinery, extend actin-rich microvilli, and complex with somatosensory axons, all hallmarks of mammalian Merkel cells. Merkel cells populate all major adult skin compartments, with region-specific densities and distribution patterns. In vivo photoconversion reveals that Merkel cells undergo steady loss and replenishment during skin homeostasis. Merkel cells develop concomitant with dermal appendages along the trunk and loss of Ectodysplasin signaling, which prevents dermal appendage formation, reduces Merkel cell density by affecting cell differentiation. By contrast, altering dermal appendage morphology changes the distribution, but not density, of Merkel cells. Overall, our studies provide insights into touch system maturation during skin organogenesis and establish zebrafish as an experimentally accessible in vivo model for the study of Merkel cell biology.