Channel activity during skin morphogenesis

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Our long-term objective is to understand the principles that orchestrate skin morphogenesis in development and wound regeneration. The understanding of biochemical signaling is well advanced. Yet, research into the roles of non-neural bioelectricity lags behind, although evidence for a role of bioelectricity in development, regeneration (McLaughlin and Levin 2018 16; Li et al., 2020 5) and wound healing (Zhao et al. 2012 32) is growing. Our research objective is to study the mechanisms underlying the development and regeneration of skin appendages. In two of our recent research papers, we were inspired to see bioelectricity in action in two tissue patterning processes. First, the orientation of elongating feather buds is regulated by synchronization of oscillating calcium channel activities in bud dermal cells, which is controlled by epidermal Shh signaling (Li et al., 2018 11). Second, the skin frequently shows pigment stripes along the body. The size and spacing of longitudinal pigmentation stripes in Japanese quail was recently shown to be controlled autonomously within melanocyte progenitor populations in a gap junction-dependent manner (Inaba et al., 2019 12). At the time these periodic black/yellow stripes form in embryos, the spacing is in millimeters, a large-scale patterning process that cannot be explained by the classical Turing reaction-diffusion mechanism (patterning in micrometer range). The results led us to think hard about how large-scale tissue architecture is built. While localized signaling centers involving morphogens (e.g., WNT, BMP, FGF) were shown to initiate periodic patterning of feather/hair buds, some unidentified mechanism capable of spanning large distances dynamically must work together to transduce the information over the long-distance scale (Inaba and Chuong, 2019 15). Bioelectricity work here provides a clue. Thus, we organized a multi-disciplinary team to analyze the mechanisms on how biochemical and bioelectric signals integrate to achieve the large-scale tissue patterning. We hypothesize, among other possibilities, transient bioelectrical signaling across gap-junction-coupled cell collectives may allow rapid, long-distance signaling with minimal decrement. Electropotential gradients are harnessed to propagate signals rapidly over the long distance (millimeters in milliseconds) to regulate intracellular messengers and pattern the much larger morphogenetic field. The developing avian skin explants provide an excellent model because of the quantifiable distinct patterns, planar topology for easier channel activity visualization, electric current perturbation and optogenetic gene activation – not easy in the mouse model. Experimentally, we will first gauge the endogenous bioelectric landscape and evaluate the importance of bioelectricity in these two tissue patterning processes (Aim 1A, 2A). Then we will study how ion channels / gap junctions cross-talk with biochemical signals to achieve tissue patterns (Aim 1B, 2B). The work is likely to produce new findings and insights for future applications to use bioelectricity to benefit wound regeneration.