Cellular and molecular regulators of melanocyte regeneration

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PROJECT SUMMARY: The proposed studies seek to isolate and characterize melanocyte stem cells (McSCs) as well as identify the signals and pathways that govern McSC-mediated melanocyte regeneration. McSC gene expression will be characterized using single-cell RNA sequencing (scRNAseq). In zebrafish we will perform longitudinal sampling of McSCs during regeneration to uncover pathways, both cell intrinsic and extrinsic, involved in determining McSC fates. scRNAseq of samples from vitiligo patients will also be performed to identify human McSCs and assess signaling active in these cells. Preliminary studies have identified novel candidate pathways in McSC biology, including NGFR signaling. This pathway is intriguing because NGFR is a marker of melanoma initiating cells and was recently found as a defining feature of dedifferentiated melanoma cells that are resistant to both immune checkpoint inhibitor and BRAF inhibitor therapies. Our data lead to the hypothesis that NGFR signaling supports the McSCs cell state and this activity is co-opted by melanoma cells in tumor maintenance and drug resistance. Functional studies in zebrafish will be used to interrogate NGFR and other candidate pathways. Pathways suspected to be important in McSC fate execution, KIT and macrophage- mediated, will be also probed using similar methodologies. Combinatorial pathway manipulations will be performed to assess how these different pathways depend on each other to regulate regeneration. scRNAseq will inform the targeted pathway studies, serve as a resource to identify new McSC-regulatory signals, and provide insight into the conservation of McSC signaling across species. This combination of experiments will provide a detailed understanding of melanocyte stem cells and the controls that guide them during the regeneration process. The specific aims of this proposal are: Aim 1: Define transcriptional changes and cellular trajectories of McSCs and other cells during regeneration Hypothesis: Regeneration is characterized by broad transcriptional changes that reflect cell state changes and engagement of regulators in response to tissue injury. Subaim 1A: Map the transcriptional and cellular changes that occur during melanocyte regeneration in zebrafish Subaim 1B: Define human McSCs and their descendants using scRNAseq of vitiligo and normal skin Aim 2: Determine and functionally analyze signaling pathways involved in McSC maintenance and melanocyte regeneration Hypothesis: A network of cellular signaling systems coordinately regulates McSC maintenance, activation and fate execution. Subaim 2A: Identify signaling pathways whose activities change in McSCs and their descendants during regeneration Subaim 2B: Functionally analyze pathways involved in McSC maintenance and activation Subaim 2C: Investigate the roles of macrophages and other intermediary cell types in regeneration