De novo apical domain formation inside the Drosophila adult midgut epithelium

Abstract: In the adult Drosophila midgut, basal intestinal stem cells give rise to enteroblasts that integrate into the epithelium as they differentiate into enterocytes. Integrating enteroblasts must generate a new apical domain and break through the septate junctions between neighboring enterocytes, while maintaining barrier function. We observe that enteroblasts form an apical membrane initiation site when they reach the septate junction between the enterocytes. Cadherin clears from the apical surface and an apical space appears above the enteroblast. New septate junctions then form laterally with the enterocytes and the AMIS develops into pre-apical compartment before it has a free apical surface in contact with the gut lumen. Finally, the enterocyte septate junction dissolves and the pre-enterocyte reaches the gut lumen with a fully-formed brush border. The process of enteroblast integration resembles lumen formation in mammalian epithelial cysts, highlighting the similarities between the fly midgut and mammalian epithelia.