Developmental regulation of intestinal best4+ cells.

best4+/CFTR-high expressing cells are a recently described intestinal epithelial cell type potentially altered in inflammatory bowel disease and colorectal cancer. However, their developmental origin, developmental regulation, and functions remain undefined. This study identifies their conserved transcriptional program and uses zebrafish to dissect their developmental regulation in vivo. Lineage tracing identified that best4+ cells arise from atoh1b+ secretory progenitors. We identify that Notch signaling, mediated by dll4, specifies best4+ cells at the expense of enterochromaffin cells. Downstream of Notch, meis1b confers best4+ cell identity. best4+ cells then exhibit regionalized gene expression, regulated by pbx3a. Additionally, this study demonstrates a system where best4+ cells can be manipulated, observed, and removed in an organismal context. Live imaging and electron microscopy of best4+ cells identified dynamic cellular projections, suggesting a sensory or communicative function. Removal of best4+ cells in vivo eliminated previously proposed functions: they are not required to restore intestinal pH following acidic challenge and do not absorb nutrients. However, we identify region-specific intracellular pH differences that suggest potential functional heterogeneity. Altogether, this study presents a comprehensive description of best4+ cell development from birth to spatial regulation that will be instrumental to understand how best4+ cells change in disease or might be therapeutically manipulated and presents the tools to dissect their function in vivo.