Characterization of gene regulation and protein interaction networks for Matrin 3 encoding mutations linked to amyotrophic lateral sclerosis and myopathy

To understand how mutations in Matrin 3 (MATR3) cause amyotrophic lateral sclerosis (ALS) and distal myopathy, we used transcriptome and interactome analysis, coupled with microscopy. Over-expression of wild-type (WT) or F115C mutant MATR3 had little impact on gene expression in neuroglia cells. Only 23 genes, expressed at levels of >100 transcripts showed >= 1.6-fold changes in expression by transfection with WT or mutant MATR3:YFP vectors. We identified similar to 123 proteins that bound MATR3, with proteins associated with stress granules and RNA processing/splicing being prominent. The interactome of myopathic S85C and ALS-variant F115C MATR3 were virtually identical to WT protein. Deletion of RNA recognition motif (RRM1) or Zn finger motifs (ZnF1 or ZnF2) diminished the binding of a subset of MATR3 interacting proteins. Remarkably, deletion of the RRM2 motif caused enhanced binding of >100 hundred proteins. In live cells, MATR3 lacking RRM2 (Delta RRM2) formed intranuclear spherical structures that fused over time into large structures. Our findings in the cell models used here suggest that MATR3 with disease-causing mutations is not dramatically different from WT protein in modulating gene regulation or in binding to normal interacting partners. The intra-nuclear localization and interaction network of MATR3 is strongly modulated by its RRM2 domain.