🧬 PubMed RNA Editing Daily Digest

CRISPR-Cas-based live-cell imaging has rapidly become a central technology for studying genome dynamics with high specificity and flexibility. By coupling nuclease-deactivated Cas (dCas) with programmable guide RNAs, genomic loci can be tracked in living cells, providing direct insights into nuclear organization and chromatin behavior. While repetitive regions such as telomeres and centromeres are readily visualized, labeling non-repetitive loci remains more challenging due to weak signals and high background. Recent advances, including multicolor labeling strategies, innovative amplification systems based on dCas9 and single-guide RNA (sgRNA) engineering, and integration with novel fluorescent reporters, have markedly expanded the applicability of CRISPR imaging across the genome. These developments have expanded the multiplexing capacity of CRISPR imaging, improved signal-to-background ratios, and even enabled the visualization of non-repetitive genomic loci. Nonetheless, key challenges remain, including cellular toxicity, replication stress, and genomic instability associated with prolonged CRISPR expression. In this review, we summarize recent advances in CRISPR live-cell imaging and highlight key design trade-offs and biological constraints.

The Faecalibaculum rodentium (Fr) CRISPR-Cas9 system exhibits enhanced gene-editing precision and efficiency compared to SpCas9, with distinctive advantages in targeting the TATA box in eukaryotic promoters. However, the underlying molecular mechanisms remained unexplored. Here, we present cryo-electron microscopy structures of the FrCas9-single guide RNA (sgRNA)-DNA complex in both the R-loop expansion and pre-catalytic states, shedding light on its specialized recognition of the 5'-NRTA-3' protospacer adjacent motif (PAM) and the unusual overwinding of the sgRNA-DNA heteroduplex. Our investigations into the structure and extensive mutational analyses reveal that the phosphate lock loop plays a pivotal role in finely adjusting FrCas9's off-target sensitivity and catalytic efficiency. Remarkably, targeted residue substitutions in the phosphate lock loop and the PAM-distal region were found to synergistically enhance both the editing precision and efficiency of FrCas9. These findings advance our understanding of Cas9's accuracy and potency mechanisms while providing a molecular foundation for the rational design and development of next-generation CRISPR technologies.

Adenosine-to-inosine (A-to-I) RNA editing by ADAR enzymes shapes transcript fate and underpins emerging RNA editing therapeutics, yet predicting which adenosines are edited remains difficult. We introduce ADAR-GPT, a model-agnostic fine-tuning framework that adapts a GPT-class language model to classify editing at candidate sites using sequence context in standardized 201 nt windows with the target adenosine explicitly marked. We train and evaluate on GTEx liver data ([Formula: see text] samples) at a clinically relevant 15% editing threshold, using a two-stage continual fine-tuning approach where lower thresholds serve as curriculum data to progressively sharpen decision boundaries. Using sequence data, ADAR-GPT demonstrates competitive or superior performance when benchmarked against established computational approaches, including convolutional and foundation model architectures, achieving a better balance of recall, precision, and specificity alongside stronger operating-curve metrics. The approach is reproducible and portable across GPT backbones without architectural changes. Beyond accurate site classification, ADAR-GPT provides practical adenosine scoring to prioritize experimental targets and inform guide RNA design, with a framework adaptable to new datasets and model architectures.

Clinical translation of CRISPR/Cas9 therapeutics is challenged by inefficient cytosolic delivery and toxicity issues associated with viral vectors and nanoparticle-based carriers. To overcome these concerns, herein we report a lipid-silica hybrid nanoparticle platform for fusogenic association and secured transfection of CRISPR/Cas9 (FAST-CRISPR), designed for rapid cytosolic delivery of CRISPR/Cas9 ribonucleoproteins, followed by efficient gene editing. Through direct fusion with the plasma membrane and bypassing conventional endocytic barriers, FAST-CRISPR nanoparticles displayed superior intracellular delivery efficacy. Optimizing lipid compositions, we discovered that a 1:1 weight mixture of cationic DOTAP and ionizable DODMA lipids, combined with tailored large-pore silica nanoparticles, enables enhanced loading capacity, rapid cytosolic dispersion, and significant nuclear transport of Cas9/gRNA complexes. FAST-CRISPR nanoparticles efficiently delivered multiplex genome-targeting ribonucleoproteins to induce targeted double-strand DNA breaks, triggering apoptosis in cancer cells and significantly suppressing tumor growth in a mouse xenograft model without systemic toxicity. Our findings demonstrate the therapeutic efficacy and translational potential of FAST-CRISPR nanoparticles as a safe and versatile non-viral delivery platform for precision genome editing.

Secreted phosphoprotein 1 (Spp1) encoding osteopontin (OPN), a matrix cell protein with pro-inflammatory and pro-necrotic tissue properties, plays a crucial role in the onset and progression of idiopathic pulmonary fibrosis (IPF). In order to treat IPF by taking advantage of Spp1, we herein developed an inhalable system composed of calcium phosphate/ poly (lactic-co-glycolic acid) (PLGA) core-shell nanoparticles which are loaded with CRISPR/Cas9 system targeting Spp1 to investigate its therapeutic potential. Specifically, the plasmid encoding Cas9 and single-guide RNA (sgRNA) selectively targeting Spp1 gene was first condensed by calcium phosphate to form Cas9 complexes, which was then encapsulated by PLGA to formulate into a gene-editing inhalable delivery system (termed CaP/Cas9/PLGA). Interestingly, the aerosolized inhaled delivery of CaP/Cas9/PLGA nanoparticles results in the effective traverse of mucosal barriers to fibrotic lungs, where they are internalized by lung cells without inducing noticeable cytotoxicity. Following endo/lysosomal escape and gene expression of CRISPR system, the disruption of Spp1 gene by Cas9/sgRNA induces the mutation frequency exceeding 30 %, resulting in efficient down-regulation of OPN level. In a bleomycin-induced pulmonary fibrosis mouse model, the inhalation of aerosolized CaP/Cas9/PLGA complexes significantly attenuates fibrosis development and improves lung function with undetectable systemic toxicity. This current study defines an innovative inhalable gene-editing formulation and offers a promising gene therapy modality for treating IPF.