Fig. 4. Dfr is required for ISNb motoneuron specification. (A) In isl^37Aa/isl^Df embryos, the ISNb motor axons fail to correctly target the ventral muscles. The arrow indicates an absence of muscle cleft innervation at muscles 12 and 13. (B) Schematic summary of wild-type and dfr phenotypes. In the wild-type embryo, the ISNb (green) and TN (blue) neurons project axons to their appropriate target areas. In dfr mutants, the ISNb motor axons do not target the ventral muscles correctly and/or project ectopically in the TN fascicle area. (C) Two hemisegments of a stage 16 Lim3B-Gal4; dfr^B129 UAS-dsdfr/+ embryo labeled with anti-Fas2 antibodies. The arrow indicates a lack of innervation at muscles 12 and 13. (D) Removing Dfr function can also cause ISNb motor axons to target the TN fascicle (arrow) in ftz_ng-Gal.20/dfr^B129 UAS-dsdfr embryos.