Effect of hFWE KO on gene expression in mature epidermal organoids

Specialized secretory cells, including keratinocytes in the last viable layers of mammalian epidermis, utilize lysosome-related organelles (LROs) to exocytose distinct cargoes vital for tissue function. Here, we demonstrate that the Flower isoform, hFWE4, a putative Ca2+ channel that permits endocytic retrieval of presynaptic vesicles and lytic granules, also resides on epidermal lamellar bodies (LBs), an LRO that extrudes a proteinaceous lipid-rich matrix to finalize the epidermal barrier. We show that hFWE4-positive LBs associate with a distinct ensemble of LRO trafficking mediators and that, in a process required for maturation of the epidermal barrier, hFWE4 elevates cytosolic Ca2+ to facilitate the apically polarized exocytosis of LBs. Finally, supporting a critical role for hFWE4-dependent trafficking in establishing the epidermal barrier, we demonstrate that this process is dysregulated in genetic diseases of cornification that are driven by impairments in keratinocyte Ca2+ handling. Our results provide new insight into the biogenesis and trafficking of epidermal LBs and more broadly suggest that hFWE4 is a core component of LRO trafficking machinery that endows Ca2+ dependency to distinct stages of the transport process depending on the cell of origin.