In Fas3^Mhc.PC embryos expressing Fas3 on all muscles (instead of the muscle 6 and 7, as in wild type) the RP3 growth cone is often seen to misinnervate incorrect muscles that lie within its filopodial reach. The morphology of junctional structures that form between the RP3 growth cone and nontarget muscles in response to this misexpression is indistinguishable from that which occurs at muscles 6 and 7 in the wild type.

Embryos expressing Fas3^Mhc.PC in the muscles show no difference in the number or overall morphology of muscles. Embryos carrying Fas3^Mhc.PC show virtually wild-type-like overall development of the nervous system. However, the RP3 neuron often fails to reach the muscle 6/7 cleft, often mistargetting to other muscles or sometimes stalling.

Innervation at the muscle 6/7 cleft is missing in 49% of cases in wild-type embryos carrying Fas3^Mhc.PC. This is largely due to the RP3 neuron innervating alternative muscles. ISN development and innervation of muscle 1 remains normal in wild-type embryos carrying Fas3^Mhc.PC. SNa innervation is normal in wild-type embryos carrying Fas3^Mhc.PC. Innervation at the muscle 6/7 cleft is missing in 53% of cases in Fas3^E25 embryos carrying Fas3^Mhc.PC. In 43% of cases RP3 growth cones extend normally and innervate the 6/7 cleft. In another 43% of cases, after reaching the target region, the RP3 growth cones stall beneath the 6/7 cleft, and in 14% of cases the RP3 growth cones mistarget nearby muscles. The 6/7 cleft lacks normal innervation in 26% of cases in third stage Fas3^E25 larvae carrying Fas3^Mhc.PC, and the membranes of muscles 6 and 7 appear tightly adhered to each other, in contrast to wild-type. Muscle 1 lacks innervation in 4% of cases in embryos carrying both Fas3^Mhc.PC and Fas3^HF-ET. The aCC growth cone stops short of muscle 1 and instead bends its head slightly posteriorly along muscle 2 in 25% of cases in these embryos. Muscle 1 lacks innervation in 12% of cases in embryos carrying both Fas3^Mhc.PC and Fas3^HF-ET and expressing Fas3^hs.PK (which is present in the P{hs-Fas3.K}HF-ET insertion) due to heat shock. The aCC growth cone mistargets muscle 2 in 30% of cases in these embryos. Abnormal axon collaterals stem out of the SNa nerve in 17% of cases in 18 hour embryos carrying both Fas3^Mhc.PC and Fas3^HF-ET. These collaterals are thin, probably consisting of only one or two axons, and misinnervate muscles 12, 13, 26 or 27.

Ectopic expression promotes muscle-muscle adhesion in vivo at a high level. Extensive muscle-muscle adhesion between subsets of ventral muscles causes defects in innervation, SNb axons reach the target region normally but the terminal abors on the internal muscle surface are greatly reduced.

Misexpression of Fas3 in all skeletal muscle cells results in no gross developmental defects of the embryonic CNS, PNS or musculature. Intracellular dye injection reveals that RP3 motor neuron often innervates 'incorrect' targets either in addition to or instead of the normal target muscle cells.