Nutrient-responsive midgut turnover is spatially controlled by serotonin signaling
Barrier epithelia undergo rapid turnover, yet how spatial tissue heterogeneity and environmental cues shape turnover rates remains poorly understood. Here, we show that serotonin signaling spatially regulates homeostatic turnover of the Drosophila midgut epithelium in a nutrient-responsive manner. Organ-wide analysis revealed regions of constitutively high and low turnover, as well as areas whose renewal depends on nutrient intake. In rapidly renewing posterior regions, serotonin accumulates in enterocytes undergoing programmed cell death (erebosis) in response to nutrient availability. Serotonin signals through the conserved 5HT7 receptor to promote enteroblast (EB) maturation and migration-associated morphological changes. 5HT7 signaling is both necessary and sufficient for renewal in high-turnover regions, and its sustained disruption leads to epithelial multilayering. Mechanistically, 5HT7 signaling regulates genes involved in metabolic pathways, such as the serine biosynthesis pathway, and in the actin cytoskeleton, which drive EB maturation and morphological change, respectively. Together, our findings establish a signaling mechanism that links nutritional cues to the spatial regulation of barrier epithelium turnover.