Fig. 3. Requirement of Egfr, btl and the MAPK pathway in branch integrity maintenance. Panels A-I and K-P show lateral views of two to five posterior tracheal metameres of stage 15 or 16 embryos focused on the DT and DBs. (A,B) The downregulation of the MAPK pathway leads to defects in the continuity of the tracheal tissue (arrows). (C) Constitutive activation of the pathway is able to rescue the branch integrity defects produced by line 801 tracheal expression. (D) Loss of pnt activity does not result in branch integrity defects. (E-G) When the Egfr signal is downregulated, branch interruptions and branches with cells only connected by cytoplasmic extensions are commonly observed (arrows). (H,I) By contrast, the downregulation of Btl does not result in a reproducible branch integrity phenotype. (J) Expressivity of the phenotypes of branch formation and branch integrity of the indicated genotypes represented as percentage of DBs affected. n is the number of DBs analysed. (K-M) Constitutive activation of the pathway results in delays in branch extension (arows in L,M) and defects in cell rearrangements (arrowheads in K,L) when visualised with different markers. (N-P) Projections of confocal sections of embryos stained with DCAD2 antibody. Some DBs show incomplete or impaired cell intercalation events as visualised, respectively, by the presence of abnormal intercellular AJs (arrows in N,O) or by stretches of intercellular AJ in regions where autocellular AJs are expected (arrow in P).