Thorax fusion phenotypes.

A to G) Thorax adult phenotypes grouped in different categories resulting from RNAi interference in the expression of selected genes. UAS-RNAi transgenes were expressed in the presumptive central area of the thorax with a Pnr-Gal4 driver. A) Wild Type adult. It shows a canonical midline fusion of the thoracic hemisegments and perfect patterning of sensory bristles B) Interference with CG14801 expression (Class 1TC phenotype) results in mirrored bristle polarity defects in the adult thorax. C) Interference with Aats-trp (CG9735) expression (Class 2TC phenotype) results in an excess of fusion with the hemithoraces collapsing at the midline. D) Interference with CG17723 expression (Class 3TC phenotype) results in a weak thorax cleft. E) Interference with CG7296 expression (Class 4TC phenotype) results in an intermediate thorax cleft. Some bristle defects are also observed. F) Interference with cpβ expression (Class 5TC phenotype) results in a big thorax cleft and scutellum abnormalities. G) Interference with Act42a (CG12051) expression (Class 6TC phenotype) results in pupal lethality and failure of discs eversion and/or fusion. Necrotic areas are found along the dorsal midline of an uneverted pupae. H to K) Expansion and fusion of imaginal discs are driven by leading edge cells, which extend long filopodia and accumulate an actin cable at the front edge. The JNK signaling pathway is activated in the leading edge cells during the fusion process. 7–7.5 h APF thoraces stained with Phalloidin (actin—red), DAPI (nuclei—blue) and Anti-LacZ (puc expression—Green). are shown. Anterior is up. H) Dorsal view of the thoracic area of a pupa which has failed to properly close upon downregulation of l(1)1Bi (CG6189) expression (Class 5TC). Phalloidin staining shows loss of actin accumulation or filopodia extensions in the leading edge of the discs, while puc-expressing cells are present along the full edge of both hemithoraces. I) Dorsal view of the thoracic area of a pupa showing irregular closure at the midline upon downregulation of CG1703 expression (Class 5TC). Phalloidin staining shows fusion defects, enlarged leading edge cells that seem to detach, which sustain strong puc expression. Picnotic nuclei are present in the scutellum area. J) Dorsal view of the thoracic area of a pupa which has failed to fully close upon downregulation of tg (CG7356) (Class 4TC). Phalloidin staining points to a clumsy accumulation of actin, most evident anteriorly. Several cells at the leading edge detach and round up and puc expression is sustained at the thorax midline. K)Aats-trp downregulation during thorax closure results in an excess of fusion (Class 2TC) that does not seem to affect actin accumulation or puc expression (dorsal thoracic area). Scale bars are indicated for each panel.