Fig. 6.

Knockdown of the SMARCB1 homologue Snr1 in hedgehog activated cells causes aberrant hedgehog as well as Notch signaling and formation of tumor-like structures in the fly model. In the larval central nervous system (a–d), Snr1RNAi enhances hedgehog signaling. In the representative images, eGFP (green) expressed with UAS promoter under control of engrailed-gal4, marks engrailed positive/hedgehog activated cells in controls (a, b; n = 12) and upon Snr1RNAi knockdown (c, d; n = 13). Note eGFP-positive cell clusters (arrows) in the brain lobes (BL) upon Snr1 knockdown not visible in control animals. In the imaginal wing disc (e–h), Snr1 knockdown causes growth defects and atypical engrailed expression pattern in the posterior compartments, visualized by eGFP (green) in controls (e; n = 16) and upon Snr1RNAi knockdown (f; n = 19). Note tumor-like structure (arrow and inset) upon Snr1RNAi knockdown. Snr1 knockdown in hedgehog activated cells also results in ectopic Notch signaling, especially in the posterior compartment of the wing disc (g, h). Expression of engrailed is reported with mRFP (shown as green) under control of the UAS/GAL4 system while activation of Notch: ‘Notch-on’ state with GFP (shown in magenta) under control of NRE (Notch responding element), in controls (g; n = 9) and in Snr1RNAi (h; n = 10). Note characteristic stripe-like Notch expression pattern at the boundary of the dorso-ventral line in controls (g) that is more intense in the engrailed-negative anterior compartment of SnrRNAi wing discs (h). In the posterior compartment of Snr1RNAi wing discs, additional ‘Notch-on’ clusters (magenta) are visible, which are frequently associated with engrailed (green) and abnormal tumor-like structures (inset). Nuclei counterstained with DAPI (blue). Scale bars denote 200 µm or 100 µm (insets). Fly genotypes are described in detail in the Materials and methods section