New research from the Rasmussen lab on the touch system in zebrafish as a new model to study Merkel cell development and maintenance was recently published in eLife. The study demonstrates that the zebrafish touch system shares many characteristics with its mammalian counterpart, including developmental origin, innervation, and molecular characteristics while allowing in vivo analysis of specification, development, and maintenance. This study is the foundation for future detailed cellular and molecular analyses of the touch sensory system and will be of interest to developmental biologists and neuroscientists studying stem cells, regeneration, and aging.
Authors on this paper include: Tanya Brown, former Rasmussen lab NSF postdoctoral fellow; Emma Horton, former Rasmussen lab research tech; Evan Craig, Biology graduate student; Camille Goo, Biology research technologist; Erik Black, MCB graduate student; Madeleine Hewitt, MCB graduate student; Nathaniel Yee, former Rasmussen lab undergraduate researcher; Everett Fan, former Rasmussen lab undergraduate researcher; David Raible, UW Biology adjunct faculty member and Departments of Biological Structure and Otolaryngology-HNS Professor; and Jeff Rasmussen, Biology Assistant Professor.
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 remains 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.