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 neighbouring enterocytes, while maintaining barrier function. We observe that enteroblasts form an apical membrane initiation site when they reach the septate junction between the overlying enterocytes. A space appears above the enteroblast as Cadherin clears from its apical surface. New septate junctions then form laterally with neighbouring enterocytes and the AMIS develops into pre-apical compartment with a fully-formed brush border. Finally, the overlying septate junction dissolves and the pre-enterocyte reaches the gut lumen. Enteroblasts therefore form an apical domain before they have a free apical surface. The process of enteroblast integration resembles lumen formation in mammalian epithelial cysts, highlighting the similarities between the fly midgut and mammalian epithelia.