Developmental regulation of intestinal <i>best4</i> + cells

<i>best4</i>+/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 <i>in vivo</i>. Lineage tracing identified that <i>best4</i>+ cells arise from <i>atoh1b</i>+ secretory progenitors. We identify that Notch signaling, mediated by <i>dll4,</i> specifies <i>best4</i>+ cells at the expense of enterochromaffin cells. Downstream of Notch, <i>meis1b</i> confers <i>best4</i>+ cell identity. <i>best4</i>+ cells then exhibit regionalized gene expression, regulated by <i>pbx3a</i>. Additionally, this study demonstrates a system where <i>best4</i>+ cells can be manipulated, observed, and removed in an organismal context. Live imaging and electron microscopy of <i>best4</i>+ cells identified dynamic cellular projections, suggesting a sensory or communicative function. Removal of <i>best4</i>+ cells <i>in vivo</i> 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 <i>best4</i>+ cell development from birth to spatial regulation that will be instrumental to understand how <i>best4</i>+ cells change in disease or might be therapeutically manipulated and presents the tools to dissect their function <i>in vivo</i>.