Heterozygous Dcc Mutant Mice Have a Subtle Locomotor Phenotype

Axon guidance receptors such as deleted in colorectal cancer (DCC) contribute to the normal formation of neural circuits, and their mutations can be associated with neural defects. In humans, heterozygous mutations in have been linked to congenital mirror movements, which are involuntary movements on one side of the body that mirror voluntary movements of the opposite side. In mice, obvious hopping phenotypes have been reported for bi-allelic mutations, while heterozygous mutants have not been closely examined. We hypothesized that a detailed characterization of heterozygous mice may reveal impaired corticospinal and spinal functions. Anterograde tracing of the motor cortex revealed a normally projecting corticospinal tract, intracortical microstimulation (ICMS) evoked normal contralateral motor responses, and behavioral tests showed normal skilled forelimb coordination. Gait analyses also showed a normal locomotor pattern and rhythm in adult mice during treadmill locomotion, except for a decreased occurrence of out-of-phase walk and an increased duty cycle of the stance phase at slow walking speed. Neonatal isolated spinal cords had normal left-right and flexor-extensor coupling, along with normal locomotor pattern and rhythm, except for an increase in the flexor-related motoneuronal output. Although mice do not exhibit any obvious bilateral impairments like those in humans, they exhibit subtle motor deficits during neonatal and adult locomotion.