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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).
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