CRISPR-Cas9 to model retinitis pigmentosa caused by mutations in splicing factors in C. Elegans

Abstract

Retinitis pigmentosa (RP) is a rare, heterogenic, and hereditary disease that produces gradual loss of the visual field and can cause blindness. Mutations causing RP are still unknown in about 50% of the cases. By CRISPR-Cas9, we mimicked a few splicing-related RP mutations (s-adRP) in PRPF8/prp-8 and SRNPN200/snpr-200 that were used for drug screens, identify potential disease modifiers, investigate mechanisms of the disease, and work on a system to provide functional information for gene variants. One of the alleles generated, displaying an overt phenotype, was used in a small-scale drug screen to identify small molecules capable of alleviating the phenotype. Unexpectedly, we found an FDA-approved drug having a detrimental effect on some of the s-adRP mutant strains. Since RP onset and progression are highly variable due to environmental or genetic modifiers, C. elegans could help RP prognosis by identifying such modifiers. We performed a small-scale RNAi screen on RP mutants with no overt phenotypes and found genetic interactions with other splicing- related genes: isy-1/ISY1, mog-2/SNRPA1, and cyn-15/PPWD1. Thus, secondary mutations in these genetic interactors could act as modifiers of the course of the disease. The mechanism by which s-adRP mutations selectively cause retinal deterioration is unknown. We detected some hints of genome instability in s-adRP mutants, which might explain the degenerative nature of the disease. We are taking steps towards establishing C. elegans as an RP diagnosis model by evaluating the functional impact of potential RP mutations, or variants of uncertain significance (VUS), in worms. For that purpose, we set a panel of features associated with s-adRP mutations, including a genetic interaction with a CRISPR-edited Slow Polymerase II mutant (ama-1(cer135[R743H])), mortal germline, or aberrant splicing events at specific transcripts. We partially humanized the sequence encoding the splicing factors prp-3 in the endogenous locus to investigate if such humanization is beneficial for functional studies of VUS. Therefore, our RP research line demonstrates the value of C. elegans for investigating rare diseases and for providing valuable information in search of drugs, diagnosis, and prognosis.