Functional classification of GNAI1 disorder variants in C. elegans uncovers conserved and cell-specific mechanisms of dysfunction

Abstract

Heterotrimeric G proteins transduce signals from G protein coupled receptors, which mediate key aspects of neuronal development and function. Mutations in the GNAI1 gene, which encodes Gi1, cause a disorder characterized by developmental delay, intellectual disability, hypotonia, and epilepsy. However, the mechanistic basis for this disorder remains unknown. Here, we show that GNAI1 is required for ciliogenesis in human cells and use C. elegans as a whole-organism model to determine the functional impact of seven GNAI1-disorder patient variants. Using CRISPR-Cas9 editing in combination with robust cellular (cilia morphology) and behavioral (chemotaxis) assays, we find that T48I, K272R, A328P, and V334E orthologous variants impact both cilia assembly and function in AWC neurons, M88V and I321T have no impact on either phenotype, and D175V exerts neuron-specific effects on cilia-dependent sensory behaviors. Finally, we validate in human ciliated cell lines that D173V, K270R, and A326P GNAI1 variants disrupt ciliary localization of the encoded human Gi1 proteins similarly to their corresponding orthologous substitutions in the C. elegans ODR-3 (D175V, K272R, and A328P). Overall, our findings determine the in vivo effects of orthologous GNAI1 variants and contribute to mechanistic understanding of GNAI1 disorder pathogenesis as well as neuron-specific roles of ODR-3 in sensory biology. ARTICLE SUMMARYG subunits of heterotrimeric G proteins transduce signaling from G protein coupled receptors and play important roles in cell communication and complex behaviors. Mutations in the GNAI1 gene, which encodes Gi1 protein, have been recently linked to a neurodevelopmental disorder; however, it remains unknown how GNAI1 patient mutations disrupt neuronal development or function to manifest in disease. We demonstrate that GNAI1 is required for ciliogenesis and use C. elegans as a whole-animal model in combination with human cells to identify cell-specific and conserved mechanisms of G dysfunction.