Fig. 4. MMP LOF mutants display inappropriate ISNb defasciculation. In each micrograph, two abdominal hemisegments of stage 17 dissected embryos stained with -FasII (A-D) or -GFP (I-L) to label the motor projections, are shown with anterior left and dorsal up. Below each image are schematics of the observed phenotypes with motor axons in brown (E-H) or black (M-P) and muscles represented by gray boxes. In addition to carrying mutations in the indicated MMP genes, embryos in I-L are heterozygous for both Hb9^Gal4 and UAS-mCD8GFP to visualize Hb9-positive axons with -GFP. (A,E,I,M) Wild-type embryos have tightly bundled axonal projections. (B,F,J,N) Mmp1^Q112*/Mmp1² mutant embryos exhibit moderate ISNb defasciculation. (C,G,K,O) ISNb-projecting axons in Mmp2^W307*/Mmp2^Df embryos are loosely bundled and frequently project aberrantly within the VLM field (arrowheads). (D,H,L,P) Mmp2^W307* Mmp1^Q112*/Mmp2^Df Mmp1² double mutants are indistinguishable from Mmp2 single mutants with frequent ectopic projections (arrowheads). Scale bar: 15 µm.