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Spacer-engineered donor DNA enhances CRISPR-Cas9-mediated knockin to establish a chemical knockdown platform for endogenous proteins.

Precise installation of functional protein domains at endogenous loci is a powerful approach for interrogating protein functions, but its broad application is limited by the low efficiency of homology-directed repair (HDR)-mediated knockin during Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 gene editing. Here, we investigated a simple donor DNA engineering strategy that enhances HDR-mediated gene knockin by appending additional gRNA-recognizable spacer sequences to donor templates. Systematic analysis of linear dsDNA and plasmid donors showed that spacer position, length, and orientation influenced HDR efficiency, and that spacer-containing donors improved knockin across multiple genomic loci, insertion sizes, cell types and delivery modalities. Mechanistic analyses revealed that spacer-containing donors formed stable complexes with Cas9/gRNA and showed increased nuclear localization, supporting nuclear delivery as a key contributor to improved editing outcomes. We then applied this gene-editing strategy to establish a chemical knockdown platform by installing drug-responsive degrons at endogenous loci, generating cell lines in which GSK3β or Lin28A protein could be rapidly, potently and reversibly depleted by drug treatment. These platforms enable selective modulation of endogenous proteins and reveal cellular responses that may differ from those obtained using conventional genetic perturbation. Together, this work establishes a readily implementable framework that integrates improved gene editing with on-demand chemical knockdown of endogenous proteins.

CRISPR-Cas9

Emerging and potential use of CRISPR in human liver disease.

CRISPR is a gene editing tool adapted from naturally occurring defense systems from bacteria. It is a technology that is revolutionizing the interrogation of gene functions in driving liver disease, especially through genetic screens and by facilitating animal knockout and knockin models. It is being used in models of liver disease to identify which genes are critical for liver pathology, especially in genetic liver disease, hepatitis, and in cancer initiation and progression. It holds tremendous promise in treating human diseases directly by editing DNA. It could disable gene function in the case of expression of a maladaptive protein, such as blocking transthyretin as a therapy for amyloidosis, or to correct gene defects, such as restoring the normal functions of liver enzymes fumarylacetoacetate hydrolase or alpha-1 antitrypsin. It is also being studied for treatment of hepatitis B infection. CRISPR is an exciting, evolving technology that is facilitating gene characterization and discovery in liver disease and holds the potential to treat liver diseases safely and permanently.

Humans

Sex-specific disruptions in PKCγ signaling in a mouse model of spinocerebellar ataxia type 14.

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant neurodegenerative disease caused by mutations in the gene encoding protein kinase C γ (PKCγ), a Ca2+- and diacylglycerol-dependent Ser/Thr kinase dominantly expressed in cerebellar Purkinje cells. These mutations impair autoinhibitory constraints to increase the basal activity of the kinase, resulting in deficits in the cerebellum that are not observed upon simple deletion of the gene, and severe ataxia. To better understand the impact of aberrant PKCγ signaling in disease pathology, we developed a knockin murine model of the SCA14 mutation ΔF48 in PKCγ. This fully penetrant mutation is severe in humans and is mechanistically informative, as it has high basal activity but is unresponsive to agonist stimulation. Genetic, behavioral, and molecular testing revealed that ΔF48 PKCγ mice have ataxia-related phenotypes and an altered cerebellar phosphoproteome driven primarily by enhanced Ca2+/calmodulin-dependent kinase 2 signaling, effects that were more severe in male mice. Analysis of existing human data revealed that SCA14 has a significantly earlier age of onset for males compared with females. Data from this clinically relevant mutation suggested that enhanced basal activity of PKCγ is sufficient to cause ataxia and that treatment strategies to modulate aberrant PKCγ may be particularly beneficial in males.

Animals

AAV-mediated CBLN1 replacement rescues hereditary ataxia caused by bi-allelic CBLN1 variants.

Cbln1 is a secreted synaptic organizer required for parallel fiber-Purkinje cell (PF-PC) synapse integrity, climbing fiber (CF) refinement, and cerebellar motor learning but has not previously been implicated in human disease. We identified bi-allelic CBLN1 missense variants (A63P and Y112C) in two unrelated families with early-onset cerebellar ataxia accompanied by oculomotor abnormalities, cerebellar atrophy, and variable cognitive delay. In heterologous cells, both variants showed reduced steady-state protein abundance, impaired maturation through the early secretory pathway, and little or no detectable secretion, resulting in markedly reduced extracellular CBLN1 availability. Consistently, cerebellar granule cells expressing CBLN1-Y112C failed to induce excitatory synapses onto glutamate receptor δ2 (GluD2)-expressing cells in vitro. A knockin mouse harboring Y112C lacked synaptic Cbln1 and recapitulated key features of Cbln1 deficiency, including disrupted PF-PC synapse organization, persistent CF multi-innervation, impaired PF-PC transmission, and long-term depression, and deficits in motor coordination and oculomotor learning. Notably, systemic delivery of an astrocyte-targeted adeno-associated virus expressing wild-type CBLN1 in adult mutant mice restored synaptic CBLN1 localization, cerebellar synaptic function, plasticity, and behavior. These findings establish CBLN1 deficiency as a cause of hereditary ataxia and identify extracellular CBLN1 replacement as a therapeutic strategy for a reversible cerebellar synaptopathy.

CBLN1

A novel DPH5-related diphthamide-deficiency syndrome causing embryonic lethality or profound neurodevelopmental disorder.

PURPOSE: Diphthamide is a post-translationally modified histidine essential for messenger RNA translation and ribosomal protein synthesis. We present evidence for DPH5 as a novel cause of embryonic lethality and profound neurodevelopmental delays (NDDs). METHODS: Molecular testing was performed using exome or genome sequencing. A targeted Dph5 knockin mouse (C57BL/6Ncrl-Dph5em1Mbp/Mmucd) was created for a DPH5 p.His260Arg homozygous variant identified in 1 family. Adenosine diphosphate-ribosylation assays in DPH5-knockout human and yeast cells and in silico modeling were performed for the identified DPH5 potential pathogenic variants. RESULTS: DPH5 variants p.His260Arg (homozygous), p.Asn110Ser and p.Arg207Ter (heterozygous), and p.Asn174LysfsTer10 (homozygous) were identified in 3 unrelated families with distinct overlapping craniofacial features, profound NDDs, multisystem abnormalities, and miscarriages. Dph5 p.His260Arg homozygous knockin was embryonically lethal with only 1 subviable mouse exhibiting impaired growth, craniofacial dysmorphology, and multisystem dysfunction recapitulating the human phenotype. Adenosine diphosphate-ribosylation assays showed absent to decreased function in DPH5-knockout human and yeast cells. In silico modeling of the variants showed altered DPH5 structure and disruption of its interaction with eEF2. CONCLUSION: We provide strong clinical, biochemical, and functional evidence for DPH5 as a novel cause of embryonic lethality or profound NDDs with multisystem involvement and expand diphthamide-deficiency syndromes and ribosomopathies.

Adenosine Diphosphate

A dual-reporter mouse for therapeutic discovery in Angelman syndrome.

Angelman syndrome is a neurodevelopmental disorder caused by loss of the maternal UBE3A allele, the sole source of UBE3A in mature neurons owing to epigenetic silencing of the paternal allele. Although emerging therapies are being developed to restore UBE3A expression by activating the dormant paternal UBE3A allele, existing mouse models for such preclinical studies have limited throughput and utility, creating bottlenecks for both in vitro therapeutic screening and in vivo characterization. To address this, we developed the Ube3a-INSG dual-reporter knockin mouse, in which an IRES-Nanoluciferase-T2A-Sun1-sfGFP (INSG) cassette was inserted downstream of the endogenous Ube3a stop codon. The INSG model preserves UBE3A protein levels and function while enabling 2 complementary allele-specific readouts: Sun1-sfGFP and Nanoluciferase. We show that Sun1-sfGFP, a nuclear envelope-localized reporter, enables single-cell fluorescence analysis, whole-brain light-sheet imaging, and nuclear quantification by flow cytometry. Further, Nanoluciferase supports high-throughput luminescence assays for sensitive pharmacological profiling in cultured neurons and noninvasive in vivo bioluminescence imaging for pharmacodynamic assessment. By combining scalable screening, cellular analysis, and real-time in vivo monitoring in a single model, the Ube3a-INSG dual-reporter mouse provides a powerful platform to accelerate therapeutic development centered on UBE3A.

Animals