CRISPR/Cas9-based repair of a heterozygous HNF1A mutation in patient-derived hiPSCs

CRISPR/Cas9-Based Genome Editing: Understanding Differences in DNA Repair Pathways, Profiles, and Outcomes

Over a decade of advances in Clustered Regularly Interspersed Short Palindromic Repeats (CRISPR) and CRISPR-associated protein 9 (Cas9)-based technologies have culminated in the first-ever FDA-approved CRISPR/Cas-based therapy. Aside from this approved therapy for sickle cell anemia, several CRISPR/Cas-based therapies are currently under development or testing for a range of chronic diseases, including viral diseases like human immunodeficiency virus type 1 (HIV-1) infection, genetic diseases like familial hypercholesterolemia, and cancer. The success of these therapies hinges on the effective delivery of CRISPR/Cas9 components to target regions, efficient Cas endonuclease editing, repair profiles generated, and their resulting outcomes. Here, we discuss the factors that influence the generation of CRISPR/Cas9-generated repair edits, the overall profiles, and outcome prediction(s), as well as the analytical tools that have been developed to date. Finally, how this technology has been used towards a functional HIV-1 cure is discussed.

CRISPR-Cas9 Technology in Genetic Disorders: Genome Editing Approaches and Therapeutic Applications – A Review

The potential application of CRISPR technology for the possible management of geneticbased conditions, including sickle-cell anemia, β-thalassemia, cystic fibrosis, and Duchenne muscular dystrophy is described.

In vivo gene disruption and homology-directed repair in muscles and muscle stem cells using CRISPR/Cas9

Programmable endonucleases such as CRISPR/Cas9 provide powerful tools to edit mammalian genomes by engaging cellular mechanisms of DNA double-strand break (DSB) repair. CRISPR-catalysed homology-directed repair (CRISPR-HDR), though generally less efficient than other modes of DNA repair, holds particular promise to enable precise sequence replacement by targeted insertion of a homologous DNA template1,2. While recent studies have reported appreciable levels of HDR in cardiomyocytes in vivo3, skeletal muscle myofibres have historically been considered refractory to HDR-mediated genome editing4. Furthermore, how repair outcomes differ across tissues after systemic delivery of CRISPR/Cas9 editors, whether precise HDR editing can be achieved in regenerative tissue stem cells, and how developmental timing influences accessibility to CRISPR-induced repair remain unclear. Here, we use an adeno-associated virus (AAV)-delivered in vivo GFP-to-BFP colour-switching reporter system (AAV-GFP-to-BFP) to examine in vivo CRISPR-HDR with cellular- and tissue-level resolution. We find that postnatal cardiac muscle, skeletal muscle, and muscle stem cells undergo templated HDR at different rates across discrete developmental stages in mice. While HDR-edited muscle stem cells and myofibres were readily detectable after in vivo editing in juvenile mice, editing in neonatal mice yielded more efficient HDR in cardiac tissue. Based on these results, we adapted the CRISPR-HDR approach to rescue the therapeutically relevant Dmd mutation in mdx mice, demonstrating recoding to the wild-type protein sequence in both skeletal and cardiac muscles. These results provide a framework for advancing donor-templated DNA repair in living postnatal animals, and reveal unexpected cellular, developmental, and disease-related constraints on precise, therapeutic in vivo gene correction.

Developing a CRISPR-based Toolkit to Study Precise Dosage Modulation of Gene Expression

CRISPR-SWITCH (silent mutations with intention to create heterozygotes): a strategy for monoallelic genome editing and generation of a Syt1-D365E mouse model of Baker–Gordon syndrome

Precise control of allelic outcomes remains a major limitation of CRISPR-Cas9 genome editing, particularly for genes in which biallelic modification is lethal or confounds disease modeling. Here, we present CRISPR-SWITCH (Silent mutations With Intention To Create Heterozygotes), a genome engineering strategy that enables deliberate monoallelic editing by exploiting allele-specific CRISPR targeting. CRISPR-SWITCH operates through the initial introduction of a synonymous nucleotide substitution that creates a unique guide RNA recognition site, allowing subsequent selective editing of the engineered allele while preserving the wildtype copy. We applied CRISPR-SWITCH to generate a mouse model of Baker-Gordon syndrome, a dominant-negative neurodevelopmental disorder caused by pathogenic variants in synaptotagmin-1 (SYT1). Conventional CRISPR-Cas9 editing of the Syt1 locus produced complex allelic outcomes characterized by biallelic editing and mosaicism, preventing reliable generation of the defined heterozygous genotype required for disease modeling. In contrast, CRISPR-SWITCH enforced heterozygosity by first introducing a synonymous Y364Y mutation and then selectively targeting this allele to install the pathogenic D365E variant. This approach produced viable Syt1-D365E mice with exclusive monoallelic genome editing, predictable preservation of a wildtype allele, and balanced (1:1) expression of mutant and wildtype transcripts. Together, these results demonstrate proof-of-principle that CRISPR-SWITCH can enforce heterozygosity at endogenous loci and enable the generation of viable mammalian models for dominant-negative and dosage-sensitive genetic disorders.

Genome-Wide CRISPR Screening Identifies Cellular Factors Controlling Nonviral Genome Editing Efficiency

A novel genome-wide CRISPR screening strategy that will facilitate the systematic engineering of novel nonviral genome editing delivery methods, where the identified novel gene hits can be further used to increase editing efficiency for other therapeutically relevant cell types.