Figure 7.
Regional Specificity of the Gut Neuron/Tracheae Interactions
(A) The different visceral tracheal terminal branches of the posterior midgut and hindgut, as visualized in green in a 3rd-instar larva using a pan-tracheal reporter to express a membrane-tagged GFP (btl>cd8-GFP). 22C10 staining (in red) highlights the two hindgut nerves and phalloidin (in blue) labels visceral muscles.
(B) Illustration summarizing the different kinds of visceral tracheal terminal cells, their positioning relative to the hindgut nerves, and their regulation by systemic and paracrine neuropeptides at the 3rd-instar stage. In the posterior midgut and anterior hindgut, there is no apparent dorsoventral patterning with regard to the positioning of tracheal terminal cells. In these intestinal portions, tracheal terminal growth is exclusively under the control of the systemic mNSC-derived Ilps. In the mid-hindgut, the visceral tracheal terminal cells reach the hindgut from its ventral side and extend branches that eventually cover the dorsal domain. Mutation of Pdf or Ilp7 alone, as well as the triple Ilp2,3,5 mutation, all lead to reduced branching. In the posterior hindgut, where the Ilp7/Pdf axons abut the posterior hindgut tracheal branches, Ilp7 is partially redundant with Pdf and the systemic Ilps.