Neuromuscular Junction Defects in a Mouse Model of Charcot-Marie-Tooth Disease Type 2O

Charcot Marie Tooth disease (CMT) represents the most common inheritable peripheral group of motor and sensory disorders; affecting 1 in 2500 people worldwide. Individuals with CMT experience slow progressing weakness of the muscle, atrophy, mild loss of motor coordination and in some cases loss of sensory function in the hands and feet which could ultimately affect mobility. Dynein is an essential molecular motor that functions to transport cargos in all cells. A point mutation in the dynein heavy chain was discovered to cause CMT disease in humans, specifically CMT type 2O. We generated a knock-in mouse model bearing the same mutation(H304R) in the dynein heavy chain to study the disease. We utilized behavioral assays to determine whether our mutant mice had a phenotype linked to CMT disease. The mutant mice had motor coordination defects and reduced muscle strength compared to normal mice. To better understand the disease pathway, we obtained homozygous mutants from a heterozygous cross, and the homozygotes show even more severe deficits compared to heterozygotes. They also developed an abnormal gait which separates them from heterozygous mice. In view of the locomotor deficits observed in mutants, we examined the neuromuscular junction (NMJ) for possible impairments. We identified defects in innervation at the later stages of the study and abnormal NMJ architecture in the muscle as well. The dysmorphology of the NMJ was again worse in the homozygous mutants with reduced complexity and denervation at all the timepoints assessed. Our homozygous dynein mutants can live up to two years and therefore make the design of longitudinal studies possible. Altogether, this mouse model provides dynein researchers an opportunity to work towards establishing the link between dynein mutations, dynein dysfunction and the onset and progression of disease