Hippo, TGF-β, and Src-MAPK pathways regulate transcription of the upd3 cytokine in Drosophila enterocytes upon bacterial infection

Abstract

Cytokine signaling is responsible for coordinating conserved epithelial regeneration and immune responses in the digestive tract. In the Drosophila midgut, Upd3 is a major cytokine, which is induced in enterocytes (EC) and enteroblasts (EB) upon oral infection, and initiates intestinal stem cell (ISC) dependent tissue repair. To date, the genetic network directing upd3 transcription remains largely uncharacterized. Here, we have identified the key infection-responsive enhancers of the upd3 gene and show that distinct enhancers respond to various stresses. Furthermore, through functional genetic screening, bioinformatic analyses and yeast one-hybrid screening, we determined that the transcription factors Scalloped (Sd), Mothers against dpp (Mad), and D-Fos are principal regulators of upd3 expression. Our study demonstrates that upd3 transcription in the gut is regulated by the activation of multiple pathways, including the Hippo, TGF-β/Dpp, and Src, as well as p38-dependent MAPK pathways. Thus, these essential pathways, which are known to control ISC proliferation cell-autonomously, are also activated in ECs to promote tissue turnover the regulation of upd3 transcription.

Ets21c Governs Tissue Renewal, Stress Tolerance, and Aging in the Drosophila Intestine

“…The cell death-independent mechanism would also explain why the ISC mitotic rate remains high in paraquat-exposed flies despite Dcp1 inactivation due to EC-specific ets21c silencing. In this respect, it is important to note that other transcription factors besides Ets21c have been shown to regulate Upd3 expression under stress conditions—for example, in infected ECs ( Houtz et al., 2017 ) or upon oncogene activation in imaginal discs ( Bunker et al., 2015 , Külshammer et al., 2015 ).…”

Polyploidy in tissue homeostasis and regeneration

“…In short, loss of Hpo activity allows nuclear localization of Yki and transcriptional activation of numerous genes involved in cell growth and other processes (Huang et al, 2005). In the fly gut, Yki also stimulates the transcription of secreted cytokines and growth factors, which stimulate Janus Kinase (JAK) and EGFR activity, respectively, promoting faster growth and endocycling in differentiating EBs (Furriols and Bray, 2001;Houtz et al, 2017;Ohlstein and Spradling, 2007;Ren et al, 2010;Shaw et al, 2010). Similarly, damage and ROS activate ISC proliferation through JNK activation in ECs, which stimulates the secretion of cytokines upon injury (Jiang et al, 2009;Santabarbara-Ruiz et al, 2015).…”

JAK/STAT signaling in stem cells and regeneration: fromDrosophilato vertebrates

“…These insults result in the production of inflammatory cytokinesparticularly Upd3by intestinal epithelial cells that drive epithelial regeneration by increasing ISC proliferation (Buchon et al, 2009a,b;Cronin et al, 2009;Jiang et al, 2009;Osman et al, 2012;Zhou et al, 2013). Recent work has identified a 4 kb enhancer that induces upd3 expression in EBs/ECs during bacterial infection or chemical injury (Houtz et al, 2017;Jiang et al, 2011;Zhou et al, 2013). During regeneration, this enhancer is upregulated by Yorkie (Yki)/Scalloped (Sd) and AP-1 (D-Jun and D-Fos) transcriptional complexes in response to several stress signals, including Jun N-terminal kinase (JNK), p38, Hippo (Hpo)/Warts (Wts) and Misshapen (Msn)/Wts (Houtz et al, 2017;Jiang et al, 2011;Karpowicz et al, 2010;Li et al, 2014;Ren et al, 2010;Shaw et al, 2010;Staley and Irvine, 2010).…”