Fig. 5. MMP LOF mutants exhibit excessive SNa defasciculation. In each micrograph, two abdominal hemisegments of stage 17 dissected embryos stained with -FasII 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 and muscles represented by gray boxes. (A,E) In wild type, the two branches of the SNa stay tightly bundled after dividing into dorsal and posterior branches and go on to correctly innervate their lateral muscle targets. (B,F) In Mmp1^Q112*/Mmp1² embryos, axons within the dorsal and posterior SNa branches project ectopically (arrowheads). (C,G) Mmp2^W307*/Mmp2^Df mutants display aberrant SNa defasciculation (arrowheads) phenotypes similar to those observed in Mmp1 mutants. (D,H) SNa-projecting axons in Mmp2^W307* Mmp1^Q112*/Mmp2^Df Mmp1² double mutant embryos branch aberrantly and are less tightly bundled (arrowheads). The penetrance of SNa defasciculation observed in MMP double mutants is increased relative to either MMP single mutant. Scale bar: 15 µm.