The septate junction component Bark beetle is required for Drosophila intestinal barrier function and homeostasis

Age-related loss of intestinal barrier function has been found across species, and the causes remain unknown. The intestinal epithelial barrier is maintained by tight junctions (TJs) in mammals and septate junctions (SJs) in insects. Specialized tricellular junctions (TCJs) are found at the nexus of three adjacent cell membranes, and we showed previously that aging results in mis-localization of the tricellular SJ (tSJ) component Gliotactin (Gli) in enterocytes (ECs) of the Drosophila melanogaster intestine. In embryonic epithelia, the tSJ protein Bark beetle (Bark) recruits Gli to tSJs, which prompted us to investigate Bark function in the intestine. Bark protein localization decreases at tSJs in aged flies. EC-specific bark depletion in young flies led to hallmarks of intestinal aging and shortened lifespan, whereas depletion of bark in progenitor cells reduced Notch activity, biasing differentiation toward the secretory lineage. Together, our data implicate Bark in EC maturation, maintenance of intestinal barrier integrity, and homeostasis. Understanding the assembly and maintenance of tSJs to ensure barrier integrity may lead to strategies to improve tissue integrity when function is compromised.