The Paracrine The Wingless And Upd, / Jak / Stat Signaling Pathway Control Drosophila Intestinal Stem Cell Self-renewal

In the adult Drosophila midgut, multipotent intestinal stem cells (ISCs) maintain tissue homeostasis by steadily producing daughters that differentiate into either enterocytes (EC) or enteroendocrine (ee) cells[1-2]. ISCs are scattered along the basement membrane composed of extracellular matrix, and are not associated with any obvious cellular niches. Notch activity is required for the differentiation of ISC daughter cells and promotes the differentiation of enteroblast (EB) into EC[3]. However, the underlying mechanisms controlling ISC self-renewal and ISC niche remain unknown. Here, we show that the canonical Wnt and JAK/STAT signaling pathways control ISC self-renewal. Wingless (Wg), a ligand of canonical Wnt signaling pathway, is specifically expressed in the muscles surrounding the gut, and able to traverse through the basement membrane and reach ISCs, where it activates a canonical Wnt signaling pathway to regulate ISC self-renewal. Reduced function of wg causes ISC quiescene and loss through differentiation. Clonal analysis shows that the main downstream components of the Wg signaling pathway, including Frizzled, Dishevelled and Armadillo are cell-autonomously required for ISC self-renewal. Wg signaling hyperactivation produces extra ISC-like and progenitor cells. Furthermore, genetic epistatic analysis suggests that Notch functions downstream of the Wg pathway, and antagonistic activities of Wg and Notch signaling pathways control the balance between self-renewal and differentiation of ISCs. Our study also shows Upd, the major ligand of the canonical JAK/STAT signaling transduction pathway, is also specifically expressed in the visceral muscles and required for ISC maintenance. And Upd, as another paracrine signal, activates a canonical JAK/STAT signaling cascade in ISCs to regulate ISC self-renewal and differentiation. Reduced downstream components of JAK/STAT signaling result in ISC quiescence and loss, whereas signaling overactivation produces extra ISC-like and progenitor cells. Simultaneous disruption or activation of both JAK and Wg signaling in ISC causes a stronger ISC loss or a greater accumulation of ISC-like cells, respectively, than by altering either pathway alone. These data indicate that the two pathways function cooperatively and in parallel. Moreover, the loss of JAK/STAT signaling causes blockage of EB differentiation, and reduced JAK signaling preferentially inhibits ee cell differentiation. Conversely, JAK overactivation produces extra differentiated cells, especially ee cells. The function analysis between JAK/STAT and Notch pathway show Notch functions downstream of JAK/STAT signaling, and the antagonistic activities of JAK/STAT and Notch pathways control the binary cell fate choice between EC and ee cells. Our study reveals the surrounding visceral muscles as ISC niche, produces Wg and Upd to activate the canonical Wg and JAK/STAT signaling pathways. These two pathways function cooperatively and in parallel to control ISC self-renewal. JAK/STAT signaling also antagonizes with Notch activity to control the binary cell fate choice of EBs.