Mapping multimodal phenotypes to perturbations in cells and tissue with CRISPRmap

A safety and absolute activity measurement method for Phi29 DNA polymerase based on chemiluminescent detection of dATP consumption

BACKGROUND

Phi29 DNA polymerase serves as a cornerstone enzyme in molecular biology, enabling critical applications such as rolling-circle amplification, multiple strand-displacement amplification, and single-molecule real-time sequencing. Despite its widespread use, traditional methods for assessing its activity-including radioactive labeling and fluorescence-based quantification-suffer from limitations such as operational complexity, low precision, and safety risks. These challenges have hindered standardized quality control in both academic and industrial settings.

RESULTS

To address these limitations, we developed a chemiluminescence-based absolute quantitation method that directly measures dATP consumption during polymerization. This method streamlines operational workflows by eliminating the need for multi-step purification procedures or specialized equipment, enabling the quantification of Phi29 DNA polymerase activity within 2 h. It demonstrates robust linearity and sensitivity across a broad dynamic range (25-200 μg/mL), while employing chemiluminescence-based detection of dATP to replace 3H-labeled dTTP, thereby eliminating biohazard risks associated with radioactive materials and enhancing feasibility for routine laboratory implementation.

SIGNIFICANCE

This method introduces a novel approach for determining DNA polymerase activity by pioneering the correlation between dATP stoichiometry and enzymatic activity. It expands the applicability of activity assays to routine molecular biology laboratories, enabling rapid inter-batch consistency testing in commercial enzyme production. This advancement establishes a new benchmark for polymerase quality control.

Sequencing-free whole genome spatial transcriptomics at molecular resolution in intact tissue

Recent breakthroughs in spatial transcriptomics technologies have enhanced our understanding of diverse cellular identities, compositions, interactions, spatial organizations, and functions. Yet existing spatial transcriptomics tools are still limited in either transcriptomic coverage or spatial resolution. Leading spatial-capture or spatial-tagging transcriptomics techniques that rely on in-vitro sequencing offer whole-transcriptome coverage, in principle, but at the cost of lower spatial resolution compared to image-based techniques. In contrast, high-performance image-based spatial transcriptomics techniques, which rely on in situ hybridization or in situ sequencing, achieve single-molecule spatial resolution and retain sub-cellular morphologies, but are limited by probe libraries that target only a subset of the transcriptome, typically covering several hundred to a few thousand transcript species. Together, these limitations hinder unbiased, hypothesis-free transcriptomic analyses at high spatial resolution. Here we develop a new image-based spatial transcriptomics technology termed Reverse-padlock Amplicon Encoding FISH (RAEFISH) with whole-genome level coverage while retaining single-molecule spatial resolution in intact tissues. We demonstrate image-based spatial transcriptomics targeting 23,000 human transcript species or 22,000 mouse transcript species, including nearly the entire protein-coding transcriptome and several thousand long-noncoding RNAs, in single cells in cultures and in tissue sections. Our analyses reveal differential subcellular localizations of diverse transcripts, cell-type-specific and cell-type-invariant tissue zonation dependent transcriptome, and gene expression programs underlying preferential cell-cell interactions. Finally, we further develop our technology for direct spatial readout of gRNAs in an image-based high-content CRISPR screen. Overall, these developments provide the research community with a broadly applicable technology that enables high-coverage, high-resolution spatial profiling of both long and short, native and engineered RNA species in many biomedical contexts.

A roadmap toward genome-wide CRISPR screening throughout the organism

Genome-wide CRISPR screening in the organism has tremendous potential to answer long-standing questions of mammalian physiology and disease. However, bringing this powerful technology in vivo presents unique challenges, including delivering a genome-wide sgRNA library to the appropriate cell type, achieving sufficient coverage of the library, and selecting for the phenotype of interest. In this review, we highlight recent advances in sgRNA delivery, library design, and phenotypic readout that can help overcome these technical challenges and thereby bring high-throughput genetic dissection to an increasing number of tissues and questions. We are excited about the potential for ongoing innovation in these areas to ultimately enable genome-wide CRISPR screening in any cell type of interest in the organism, allowing for unprecedented investigation into diverse questions of mammalian physiology and disease.

Massively parallel in vivo Perturb-seq screening

Advances in genomics have identified thousands of risk genes impacting human health and diseases, but the functions of these genes and their mechanistic contribution to disease are often unclear. Moving beyond identification to actionable biological pathways requires dissecting risk gene function and cell type-specific action in intact tissues. This gap can in part be addressed by in vivo Perturb-seq, a method that combines state-of-the-art gene editing tools for programmable perturbation of genes with high-content, high-resolution single-cell genomic assays as phenotypic readouts. Here we describe a detailed protocol to perform massively parallel in vivo Perturb-seq using several versatile adeno-associated virus (AAV) vectors and provide guidance for conducting successful downstream analyses. Expertise in mouse work, AAV production and single-cell genomics is required. We discuss key parameters for designing in vivo Perturb-seq experiments across diverse biological questions and contexts. We further detail the step-by-step procedure, from designing a perturbation library to producing and administering AAV, highlighting where quality control checks can offer critical go-no-go points for this time- and cost-expensive method. Finally, we discuss data analysis options and available software. In vivo Perturb-seq has the potential to greatly accelerate functional genomics studies in mammalian systems, and this protocol will help others adopt it to answer a broad array of biological questions. From guide RNA design to tissue collection and data collection, this protocol is expected to take 9-15 weeks to complete, followed by data analysis.

NIS-Seq enables cell-type-agnostic optical perturbation screening

Optical pooled screening offers a broader-scale alternative to enrichment-based perturbation screening, using fluorescence microscopy to correlate phenotypes and perturbations across single cells. Previous methods work well in large, transcriptionally active cell lines, because they rely on cytosolic detection of endogenously expressed barcoded transcripts; however, they are limited by reliable cell segmentation, cytosol size, transcriptional activity and cell density. Nuclear In-Situ Sequencing (NIS-Seq) expands this technology by creating bright sequencing signals directly from nuclear genomic DNA to screen nucleated cells at high density and high library complexity. By inserting an inverted phage promoter downstream of the single guide RNA (sgRNA), many RNA copies of the sgRNA can be generated and sequenced independently of cellular transcription. In this study, we benchmarked NIS-Seq across eight cell types from two species and performed four genome-scale optical perturbation screens, identifying key players of inflammation-related cellular pathways. Finally, we performed a small-scale pooled optical screen in primary human macrophages from blood of healthy donors and demonstrated barcode identification in lentivirally transduced human skin tissue.