Basal stem cell progeny establish their apical surface in a junctional niche during turnover of an adult barrier epithelium

Galenza et al. show that basal stem cell progeny seamlessly integrate into a physiologically active barrier epithelium by gestating their future apical surface in a sheltering niche created by a transient occluding junction. Barrier epithelial organs face the constant challenge of sealing the interior body from the external environment while simultaneously replacing the cells that contact this environment. New replacement cells-the progeny of basal stem cells-are born without barrier-forming structures such as a specialized apical membrane and occluding junctions. Here, we investigate how new progeny acquire barrier structures as they integrate into the intestinal epithelium of adult Drosophila. We find they gestate their future apical membrane in a sublumenal niche created by a transitional occluding junction that envelops the differentiating cell and enables it to form a deep, microvilli-lined apical pit. The transitional junction seals the pit from the intestinal lumen until differentiation-driven, basal-to-apical remodelling of the niche opens the pit and integrates the now-mature cell into the barrier. By coordinating junctional remodelling with terminal differentiation, stem cell progeny integrate into a functional, adult epithelium without jeopardizing barrier integrity.

Automated summary

Galenza et al. demonstrate that progeny of basal stem cells in the intestinal epithelium of adult Drosophila seamlessly integrate into a physiologically active barrier by gestating their future apical surface in a sheltering niche. They find that a transitional occluding junction creates a sublumenal niche where the differentiating cell develops a deep apical pit with microvilli-lined membrane, which is then integrated into the barrier through remodelling of the niche. This study highlights the importance of coordinating junctional remodelling with cell differentiation to ensure the integration of stem cell progeny into a functional epithelium without compromising barrier integrity.