A recessive Trim2 mutation causes an axonal neuropathy in mice

We analyzed Trim2^A/A mice, generated by CRISPR-Cas9, which have a recessive, null mutation of Trim2. Trim2^A/A mice develop ataxia that is associated with a severe loss of cerebellar Purkinje cells and a peripheral neuropathy. Myelinated axons in the CNS, including those in the deep cerebellar nuclei, have focal enlargements that contain mitochondria and neurofilaments. In the PNS, there is a loss of myelinated axons, particularly in the most distal nerves. The pathologically affected neuronal populations - primary sensory and motor neurons as well as cerebellar Purkinje cells - express TRIM2, suggesting that loss of TRIM2 in these neurons results in cell autonomous effects on their axons. In contrast, these pathological findings were not found in a second strain of Trim2 mutant mice (Trim2^C/C), which has a partial deletion in the RING domain that is needed for ubiquitin ligase activity. Both the Trim2^Aand the Trim2^C alleles encode mutant TRIM2 proteins with reduced ubiquitination activity. In sum, Trim2^A/A mice are a genetically authentic animal model of a recessive axonal neuropathy of humans, apparently for a function that does not depend on the ubiquitin ligase activity.