SUMMARY Stem cell division is essential for tissue integrity during growth, aging, and pathogenic assaults. Adult gastrointestinal tract encounters numerous stimulations and impaired tissue regeneration may lead to inflammatory diseases and cancer. Intestinal stem cells in adult Drosophila have recently been identified and shown to replenish the various cell types within the midgut. However, it is not known whether these intestinal stem cells can respond to environmental challenges. By feeding dextran sulfate sodium and bleomycin to flies and by expressing apoptotic proteins, we show that Drosophila intestinal stem cells can increase the rate of division in response to tissue damage. Moreover, if tissue damage results in epithelial cell loss, the newly formed enteroblasts can differentiate into mature epithelial cells. By using this newly established system of intestinal stem cell proliferation and tissue regeneration, we find that the insulin receptor signaling pathway is required for intestinal stem cell division.

Summary Apoptosis-induced proliferation (AiP) is a compensatory mechanism to maintain tissue size and morphology following unexpected cell loss during normal development, and may also be a contributing factor to cancer and drug resistance. In apoptotic cells, caspase-initiated signaling cascades lead to the downstream production of mitogenic factors and the proliferation of neighbouring surviving cells. In epithelial cells of Drosophila imaginal discs, the Caspase-9 ortholog Dronc drives AiP via activation of Jun N-terminal kinase (JNK); however, the specific mechanisms of JNK activation remain unknown. Here, we show that caspase-induced activation of JNK during AiP depends on an inflammatory response. This is mediated by extracellular reactive oxygen species (ROS) generated by the NADPH oxidase Duox in epithelial disc cells. Extracellular ROS activate Drosophila macrophages (hemocytes), which in turn trigger JNK activity in epithelial cells by signaling through the TNF ortholog Eiger. We propose that in an immortalized (‘undead’) model of AiP, signaling back and forth between epithelial disc cells and hemocytes by extracellular ROS and TNF/Eiger drives overgrowth of the disc epithelium. These data illustrate a bidirectional cell/cell communication pathway with implication for tissue repair, regeneration and cancer.

SUMMARY Similar to the mammalian intestine, the Drosophila adult midgut has resident stem cells that support growth and regeneration. How the niche regulates intestinal stem cell activity in both mammals and flies is not well understood. Here we show that the conserved germinal center protein kinase Misshapen restricts intestinal stem cell division by repressing the expression of the JAK-STAT pathway ligand Upd3 in differentiating enteroblasts. Misshapen, a distant relative to the prototypic Warts activating kinase Hippo, interacts with and activates Warts to negatively regulate the activity of Yorkie and the expression of Upd3. The mammalian Misshapen homolog MAP4K4 similarly interacts with LATS (Warts homolog) and promotes inhibition of YAP (Yorkie homolog). Together, this work reveals that the Misshapen-Warts-Yorkie pathway acts in enteroblasts to control niche signaling to intestinal stem cells. These findings also provide a model in which to study requirements for MAP4K4-related kinases in MST1/2-independent regulation of LATS and YAP.

COVID-19 caused by SARS-CoV-2 has become a global pandemic requiring the development of interventions for the prevention or treatment to curtail mortality and morbidity. No vaccine to boost mucosal immunity, or as a therapeutic, has yet been developed to SARS-CoV-2. In this study, we discover and characterize a cross-reactive human IgA monoclonal antibody, MAb362. MAb362 binds to both SARS-CoV and SARS-CoV-2 spike proteins and competitively blocks ACE2 receptor binding, by overlapping the ACE2 structural binding epitope. Furthermore, MAb362 IgA neutralizes both pseudotyped SARS-CoV and SARS-CoV-2 in 293 cells expressing ACE2. When converted to secretory IgA, MAb326 also neutralizes authentic SARS-CoV-2 virus while the IgG isotype shows no neutralization. Our results suggest that SARS-CoV-2 specific IgA antibodies, such as MAb362, may provide effective immunity against SARS-CoV-2 by inducing mucosal immunity within the respiratory system, a potentially critical feature of an effective vaccine.