Elucidating the tissue damage-sensing mechanism that maintains Drosophila midgut homeostasis. Julieta A. Maldera, Bruce A. Edgar. DKFZ-ZMBH Alliance, Heidelberg, Germany.

   Maintenance of epithelial homeostasis relies on a tightly coordinated process that involves the balance between removing damaged cells and producing new cells from resident stem cells. To ensure optimal epithelial regeneration while preventing dysplasia, the proliferation and differentiation rate of the stem cells has to be linked to tissue needs. In Drosophila melanogaster, the integrity of the midgut epithelium is preserved by intestinal stem cells (ISCs), by means of their ability to self-renew and produce differentiated cells. As in the mammalian colon and small intestine, the epithelium lining of the fly midgut has a rapid turnover rate due to its constant exposure to environmental toxins and pathogens. Interestingly, ISC proliferation can be further increased in response to damage and infection. The injured midgut produces Unpaired cytokines and Epidermal Growth Factor Receptor (EGFR) ligands that promote ISC division and differentiation, leading to tissue regeneration. However, how the intestinal epithelium senses the damage in the first place and translates this signal into a regenerative response remains mostly unknown. Here we propose to extend this research by identifying and characterizing genes that act as signaling molecules to translate the damage information into mitogen production. To achieve this objective, we performed fly midgut gene expression profile by mRNA deep sequencing either in healthy tissue or after gut epithelial injury (specifically, bacterial infection, heat shock, oxidative stress, induction of apoptosis, and JNK-mediated stress). The comparative analysis of this data allowed us to determine a subset of candidate genes that may be implicated in triggering mitogen secretion upon injury. Currently, we are performing a targeted UAS-RNAi screen in order to confirm the involvement of these genes during midgut regeneration. Understanding how an epithelium senses damaged cells and thereby regulates stem cell proliferation will provide insights into the basis of tissue homeostasis and regeneration.