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

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 Gαi1, 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 Caenorhabditis elegans as a whole-organism model to determine the functional impact of 7 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 Gαi1 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 the mechanistic understanding of GNAI1-disorder pathogenesis as well as neuron-specific roles of ODR-3 in sensory biology.