Fig. 2. The Nrv2 extracellular domain mediates SJ organization and tracheal tube morphogenesis. (A,B) When compared with wild-type (WT) animals (A1-5), nrv2[23B]-null mutants have tracheal defects including dorsal trunks (DTs) of increased length and irregular diameter (B1 versus A1) and lumenal staining gaps in ganglionic branches (GBs) (asterisks in B2 versus brackets in A2). nrv2 mutants have also lost the paracellular barrier function of the SJs which allows a dye to penetrate the epithelium and accumulate in the lumen (red tracheal tube in B3 versus A3 where the trachea exclude the dye). Dashed lines delineate tracheal lumen. nrv2 mutants also have disorganized SJs at the cellular level with reduced and partially mislocalized Coracle (B4 versus A4,A5). Lateral mislocalization of Coracle in the nrv2 mutant (B6, arrowhead) is apparent in overexposed images that saturate signal levels for Coracle in WT animals (B5); B5 and B6 are higher gain images of A5 and B4, respectively. (C-E) The mutant phenotypes are rescued by expression of Nrv2 (C1-4) but not by expression of Nrv1 (D1-4) or Nrv3 (E1-4) using a da-Gal4 driver. Neither Nrv1 nor Nrv3 are incorporated into an established SJ in nrv2 heterozygotes (D5,E5), whereas Nrv2 is incorporated (C5). (F,G) A chimera with the intracellular (I) and transmembrane (T) domains of Nrv3 and the extracellular (E) domain of Nrv2 rescued the nrv2 defects (F1-4), whereas a chimera with the Nrv2 IT and Nrv3 E domains did not (G1-4). Both chimeras could be incorporated into established SJs (F5,G5). Coracle is green and Nrv protein is red (anti-Nrv2.1 in A4-C5 and G4,5; anti-Nrv1 in D4,5; anti-Nrv3 in E4-F5). All animals are stage 16. Scale bars: in G2, 10 µm for A-G images 1,2; in G3, 10 µm for A-G image 3; in A5, 5 µm for A-G images 4,5 and B6.