Identifying the molecular mechanisms of GEMIN5 mutations in a novel cerebellar ataxia syndrome

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Abstract GEMIN5, an RNA-binding protein, is essential for assembly of the Survival Motor Neuron (SMN) complex. GEMIN5 facilitates the formation of small nuclear ribonucleoproteins (snRNPs; the building blocks of spliceosomes). We identified novel autosomal recessive variants in the GEMIN5 gene in multiple patients presenting with motor dysfunction, ataxia, and cerebellar atrophy. Our proposed studies are aimed to understand the molecular mechanisms of mutant GEMIN5 responsible for causing the neurological abnormalities in our patients. We found that patient a significant decrease in GEMIN5 protein levels and reduced protein stability in patient iPSC neurons suggesting a possible loss of function mechanism. Our in vitro assembly assay showed that GEMIN5 variants perturb snRNP assembly formation. To understand the consequences of loss of function GEMIN5, we knockdown endogenous rigor mortis, the Drosophila homologue of human GEMIN5, in Drosophila. Knockdown of rigor mortis (rig) caused motor dysfunction, reduced life span and developmental delay. Interestingly, we observed that CoQ10 levels were significantly reduced in human patient cells and our drosophila model. Treatment with CoQ10 reduced the disease course in human GEMIN5 patients. We generated a mouse model of Gemin5 using CRISPR/cas9 and found early lethality in mice. Our proposed studies are aimed to understand the molecular mechanisms of GEMIN5 by 1) conducting functional analysis of mutant GEMIN5 patient neurons; 2) examining if GEMIN5 variants cause mitochondrial dysfunctions in vivo and iPSC neurons; and 3) investigating the mechanisms of GEMIN5 mutations in mouse models. We expect to identify the molecular pathways that are perturbed in human patients.