Fig. 2. Transheterozygous combinations between isl, Lim3 and dfr show motoneuron innervation defects. In each panel, the dissected embryos are at stage 16 and stained with anti-Fas2 antibodies. The ventral nerve cord is towards the left, anterior is upwards. (A) In the wild-type embryo, the ISNb motoneurons innervate muscles 6, 7, 12 and 13 in a stereotypical fashion, extending processes into the muscle clefts. (B) In isl^37Aa Lim3^BD6/+; dfr^B129/+ embryos, the ISNb motoneurons fail to project to and innervate their specific target muscles, including muscles 12 and 13 (arrow). (C) Muscle innervation is also affected in isl^37Aa/+; dfr^B129/+ embryos (arrow) and in some hemisegments, the ISNb motor axons target the TN fascicle (arrowhead). (D) Lim3^BD6/+; dfr^B129/+ embryos also show severe defects in motor axon targeting and muscle innervation (arrow).