Identification of a new candidate gene in the insurgence of leukodystrophies

Leukodystrophies are a heterogeneous group of genetic disorders characterized by degeneration of the white matter in the brain, resulting in motor disabilities, muscle rigidity and even mental retardation and altered sight and/or hearing. Even though around 50% of cases were associated with specific gene mutations, the etiology of the remaining 50% is still unknown. In this work we took advantage of the zebrafish model to assess the pathogenicity of the mutation of a new candidate gene (hereafter gene A), identified in patients affected by leukodystrophy. By both injection of gene A-specific morpholino (gene A-MO) and CRISPR/Cas9 targeted mutagenesis of the zebrafish gene A orthologue, we observed that gene A loss-of-function in zebrafish embryos resulted in a leukodystrophy-like phenotype, characterized by cephalic defects and reduced or absent touch-evoked response. Moreover, both RT-qPCR and whole-mount in situ hybridization analysis indicated a reduction in the expression of genes involved with myelination, namely oligodendrocyte transcription factor 2 (olig2) and myelin basic protein (mbp), and ultrastructure analysis by transmission electron microscopy revealed alterations in myelin formation. Interestingly, morphological, molecular and ultrastructural defects in gene A-MO embryos were rescued by co-injection with zebrafish wild-type, human wild-type but not human mutated gene A full-length transcripts. Our results strongly suggest a functional role for gene A in the myelination process that could be impaired in leukodystrophies. Thereby, future studies will be aimed at assessing more in depth its role in order to better understand the pathomechanisms underlying leukodystrophies insurgence.