The Drosophila AWP1 ortholog Doctor No regulates JAK/STAT signaling for left-right asymmetry in the gut by promoting receptor endocytosis

ABSTRACT Many internal Drosophila organs show stereotypical left-right (LR) asymmetry, for which the underlying mechanisms remain elusive. Here, we identified an evolutionarily conserved ubiquitin-binding protein, AWP1/Doctor no (Drn), as a novel factor required for the LR asymmetry of the embryonic anterior gut in Drosophila . We showed that drn is essential in the circular visceral muscle cells of the midgut for JAK/STAT signaling, which contributes to the first known cue for anterior gut lateralization via LR-asymmetric nuclear rearrangement. Embryos homozygous for drn and lacking its maternal contribution showed phenotypes similar to that of depleted JAK/STAT signaling, suggesting that Drn is a general component of JAK/STAT signaling. The absence of Drn resulted in the specific accumulation of Domeless (Dome), the receptor of JAK/STAT signaling, in intracellular compartments. Thus, Drn is required for the endocytic trafficking of Dome, which is subsequently degraded in lysosomes. Our results suggest that the endocytosis of Dome is a critical step in activating JAK/STAT signaling. The roles of AWP1/Drn in activating JAK/STAT signaling and in LR-asymmetric development may be conserved in various organisms. Summary Statement Dr. No, a Drosophila ortholog of AWP1, activates JAK/STAT signaling via Dome receptor endocytosis in a crucial step for left-right asymmetry in the developing gut.