Remote Control of Intestinal Stem Cell Activity by Haemocytes in Drosophila

Abstract

The JAK/STAT pathway is a key signaling pathway in the regulation of development and immunity in metazoans. In contrast to the multiple combinatorial JAK/STAT pathways in mammals, only one canonical JAK/STAT pathway exists in Drosophila. It is activated by three secreted proteins of the Unpaired family (Upd): Upd1, Upd2 and Upd3. Although many studies have established a link between JAK/STAT activation and tissue damage, the mode of activation and the precise function of this pathway in the Drosophila systemic immune response remain unclear. In this study, we used mutations in upd2 and upd3 to investigate the role of the JAK/STAT pathway in the systemic immune response. Our study shows that haemocytes express the three upd genes and that injury markedly induces the expression of upd3 by the JNK pathway in haemocytes, which in turn activates the JAK/STAT pathway in the fat body and the gut. Surprisingly, release of Upd3 from haemocytes upon injury can remotely stimulate stem cell proliferation and the expression of Drosomycin-like genes in the intestine. Our results also suggest that a certain level of intestinal epithelium renewal is required for optimal survival to septic injury. While haemocyte-derived Upd promotes intestinal stem cell activation and survival upon septic injury, haemocytes are dispensable for epithelium renewal upon oral bacterial infection. Our study also indicates that intestinal epithelium renewal is sensitive to insults from both the lumen and the haemocoel. It also reveals that release of Upds by haemocytes coordinates the wound-healing program in multiple tissues, including the gut, an organ whose integrity is critical to fly survival.

The Drosophila CD36 Homologue croquemort Is Required to Maintain Immune and Gut Homeostasis during Development and Aging

“…Our results reinforce the possibility of an interaction between plasmatocyte function and gut homeostasis, and suggests that cytokines derived from hemocytes can trigger cell responses in the gut. These results are also in agreement with a recent publication showing that Upd3 from hemocytes can trigger intestinal stem cell proliferation [69]. Altogether, these results demonstrate that the interaction between hemocytes and the gut tissue are central to host health, and our data demonstrate that phagocytic defects can be associated with chronic gut inflammation and aberrant intestinal stem cell turn-over.…”

“…Upd3, the Drosophila analogue of IL-6, can induce the JAK-STAT pathway, which regulates the systemic immune response and metabolic homeostasis in the fat body, as well as gut homeostasis [6,22,69,70]. Using RT-qPCR, we asked whether crq is required for upd3 expression upon Ecc15 infection.…”

Actin is an evolutionarily-conserved damage-associated molecular pattern that signals tissue injury in Drosophila melanogaster

“…Actin injection did not lead to the expression of the AMP genes Drs and Dpt , which were induced only upon experimental fungal or bacterial infection (Figure 2g, h). This indicates the absence of microbial contaminants in actin preparations and demonstrates that the response to actin differs from that to septic injury, in which induction of STAT targets is invariably accompanied by that of genes downstream of Toll or Imd (Agaisse et al, 2003; Chakrabarti et al, 2016; Brun et al, 2006). In this regard, TotM induction by actin was much greater than that elicited by injury (clean or septic) or by heat shock, which are classically regarded as inducers of the JAK-STAT signalling pathway (Agaisse et al, 2003; Chakrabarti et al, 2016) (Figure 2—figure supplement 1a and data not shown).

10.7554/eLife.19662.004Figure 2.G- and F-actin induce a unique sterile inflammatory response upon injection into Drosophila.

…”

“…Upd3 produced by haemocytes is essential to induce STAT responses in the fat body or in the intestine of flies subjected to septic injury or a high fat diet (Agaisse et al, 2003; Chakrabarti et al, 2016; Woodcock et al, 2015). To determine if haemocytes were similarly required for the fat body STAT response to actin, we genetically ablated them in adult flies using two haemocyte-specific ( croquemort or Hemolectin ) temperature-sensitive Gal80 ts -Gal4 drivers crossed to a UAS- rpr strain encoding Reaper, a protein that induces apoptosis.…”

“…Despite being commonly used as a marker of STAT activation, the function of Tot and Tep proteins in Drosophila is unknown. Nevertheless, genetic loss-of-function studies have implicated JAK/STAT signaling in resistance and/or tolerance to viral, bacterial and parasitoid infections (Yang et al, 2015; Agaisse et al, 2003; Agaisse and Perrimon, 2004; Brun et al, 2006; Dostert et al, 2005; Lamiable et al, 2016; Chakrabarti et al, 2016; Kemp et al, 2013; Merkling et al, 2015). Furthermore, the JAK/STAT pathway has a well-established role in maintenance of fly intestinal homeostasis, both at steady state and following infection or injury (Biteau et al, 2011; Kohlmaier et al, 2015; Jiang et al, 2009; Micchelli and Perrimon, 2006; Zhou et al, 2013; Osman et al, 2012; Jiang et al, 2011; Beebe et al, 2010; Lin et al, 2010; Zhai et al, 2015).…”