Characterization of a novel zebrafish model of MTMR5-associated Charcot-Marie-Tooth disease type 4B3.

Biallelic loss of expression/function variants in MTMR5/SBF1 cause the inherited peripheral neuropathy Charcot-Marie-Tooth type 4B3. There is an incomplete understanding of the disease pathomechanism(s) underlying Charcot-Marie-Tooth type 4B3, and despite its severe clinical presentation, currently no disease-modifying therapies. A key barrier to the study of Charcot-Marie-Tooth type 4B3 is the lack of pre-clinical models that recapitulate the clinical and pathologic features of the disease. To address this barrier, we generated a zebrafish Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9 mutant line with a full gene deletion of mtmr5. Resulting homozygous deletion zebrafish are born at normal Mendelian ratios and have preserved motor function. However, starting by 10 days post-fertilization, mutant zebrafish develop obvious morphometric changes in head size and brain volume. These changes are accompanied at the pathological level by abnormal axon outgrowths and by the presence of dysmyelination changes reminiscent of the nerve pathology in human Charcot-Marie-Tooth type 4B3. Importantly, RNA sequencing from brain-enriched samples identifies novel disease pathways including transcriptional changes in genes responsible for neurogenesis, chromatin remodelling/organization, and synaptic membrane homeostasis. Overall, our mtmr5 knockout zebrafish mirror genetic, clinical and pathologic features of human Charcot-Marie-Tooth type 4B3. As such, it represents a first pre-clinical model to phenocopy the disease, and an ideal tool for future studies on disease pathomechanism(s) and therapy development.