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High-order three-dimensional (3D) interactions between more than two genomic loci are common in human chromatin, but their role in gene regulation is unclear. Previous high-order 3D chromatin assays either measure distant interactions across the genome or proximal interactions at selected targets. To address this gap, we developed Pore-C, which combines chromatin conformation capture with nanopore sequencing of concatemers to profile proximal high-order chromatin contacts at the genome scale. We also developed the statistical method Chromunity to identify sets of genomic loci with frequencies of high-order contacts significantly higher than background (‘synergies’). Applying these methods to human cell lines, we found that synergies were enriched in enhancers and promoters in active chromatin and in highly transcribed and lineage-defining genes. In prostate cancer cells, these included binding sites of androgen-driven transcription factors and the promoters of androgen-regulated genes. Concatemers of high-order contacts in highly expressed genes were demethylated relative to pairwise contacts at the same loci. Synergies in breast cancer cells were associated with tyfonas, a class of complex DNA amplicons. These results rigorously link genome-wide high-order 3D interactions to lineage-defining transcriptional programs and establish Pore-C and Chromunity as scalable approaches to assess high-order genome structure. High-order chromatin contacts are identified using a combination of 3C, nanopore sequencing and robust statistical analysis.

Fluorescence in situ hybridization (FISH) reveals the abundance and positioning of nucleic acid sequences in fixed samples. Despite recent advances in multiplexed amplification of FISH signals, it remains challenging to achieve high levels of simultaneous amplification and sequential detection with high sampling efficiency and simple workflows. Here we introduce signal amplification by exchange reaction (SABER), which endows oligonucleotide-based FISH probes with long, single-stranded DNA concatemers that aggregate a multitude of short complementary fluorescent imager strands. We show that SABER amplified RNA and DNA FISH signals (5- to 450-fold) in fixed cells and tissues. We also applied 17 orthogonal amplifiers against chromosomal targets simultaneously and detected mRNAs with high efficiency. We then used 10-plex SABER-FISH to identify in vivo introduced enhancers with cell-type-specific activity in the mouse retina. SABER represents a simple and versatile molecular toolkit for rapid and cost-effective multiplexed imaging of nucleic acid targets.Using primer-exchange reactions, SABER extends FISH probes with repetitive sequences that can accommodate multiple fluorescent imager strands, resulting in up to 450-fold signal amplification. SABER is showcased in DNA and RNA FISH experiments across a range of complex biological samples.

Bacteriophages are the main vehicle for gene swapping in bacteria, notoriously of pathogenicity islands and antibiotic resistance genes. Chen et al. noticed that the Staphylococcus aureus prophages do not excise from their host's genome until very late in their life cycles (see the Perspective by Davidson). Thus, the phage DNA is amplified while embedded in the bacterial chromosome. The resulting concatemers are processively packed into virus capsules while still integrated in the host chromosome. Each virion is only set loose when the capsule has reached physical capacity—a process called “headful” packaging. In situ amplification maximizes viral replication, and the headful mechanism means adjacent bacterial-host DNA also gets grabbed to fill the capsule. This process ensures that host genes are transmitted along with the phage. Science , this issue p. 207 ; see also p. 152 Staphylococcus aureus phages amplify and package while chromosomally integrated such that host DNA becomes incorporated in the virus particle. Genetic transduction is a major evolutionary force that underlies bacterial adaptation. Here we report that the temperate bacteriophages of Staphylococcus aureus engage in a distinct form of transduction we term lateral transduction. Staphylococcal prophages do not follow the previously described excision-replication-packaging pathway but instead excise late in their lytic program. Here, DNA packaging initiates in situ from integrated prophages, and large metameric spans including several hundred kilobases of the S. aureus genome are packaged in phage heads at very high frequency. In situ replication before DNA packaging creates multiple prophage genomes so that lateral-transducing particles form during normal phage maturation, transforming parts of the S. aureus chromosome into hypermobile regions of gene transfer.

CRISPR–Cas9 paired with adeno-associated virus serotype 6 (AAV6) is among the most efficient tools for producing targeted gene knockins. Here, we report that this system can lead to frequent concatemeric insertions of the viral vector genome at the target site that are difficult to detect. Such errors can cause adverse and unreliable phenotypes that are antithetical to the goal of precision genome engineering. The concatemeric knockins occurred regardless of locus, vector concentration, cell line or cell type, including human pluripotent and hematopoietic stem cells. Although these highly abundant errors were found in more than half of the edited cells, they could not be readily detected by common analytical methods. We describe strategies to detect and thoroughly characterize the concatemeric viral vector insertions, and we highlight analytical pitfalls that mask their prevalence. We then describe strategies to prevent the concatemeric inserts by cutting the vector genome after transduction. This approach is compatible with established gene editing pipelines, enabling robust genetic knockins that are safer, more reliable and more reproducible. AAV vectors form difficult-to-detect concatemers at Cas9 target sites.

The high-order three-dimensional (3D) organization of regulatory genomic elements provides a topological basis for gene regulation, but it remains unclear how multiple regulatory elements across the mammalian genome interact within an individual cell. To address this, herein, we developed scNanoHi-C, which applies Nanopore long-read sequencing to explore genome-wide proximal high-order chromatin contacts within individual cells. We show that scNanoHi-C can reliably and effectively profile 3D chromatin structures and distinguish structure subtypes among individual cells. This method could also be used to detect genomic variations, including copy-number variations and structural variations, as well as to scaffold the de novo assembly of single-cell genomes. Notably, our results suggest that extensive high-order chromatin structures exist in active chromatin regions across the genome, and multiway interactions between enhancers and their target promoters were systematically identified within individual cells. Altogether, scNanoHi-C offers new opportunities to investigate high-order 3D genome structures at the single-cell level. scNanoHi-C combines Nanopore long-read sequencing with a proximity-ligation-based Hi-C protocol to profile high-order genome structures in individual cells, enabling the capture of multiway interactions among enhancers and promoters.

Phage satellites are bacterial genetic elements that co-opt phage machinery for their own dissemination. Here we identify a family of satellites, named Phage-Inducible Chromosomal Minimalist Islands (PICMIs), that are broadly distributed in marine bacteria of the family Vibrionaceae. A typical PICMI is characterized by reduced gene content, does not encode genes for capsid remodelling, and packages its DNA as a concatemer. PICMIs integrate in the bacterial host genome next to the fis regulator, and encode three core proteins necessary for excision and replication. PICMIs are dependent on virulent phage particles to spread to other bacteria, and protect their hosts from other competitive phages without interfering with their helper phage. Thus, our work broadens our understanding of phage satellites and narrows down the minimal number of functions necessary to hijack a tailed phage. Phage satellites are bacterial genetic elements that co-opt phage machinery for their own dissemination. Here, Barcia-Cruz et al. identify a family of satellites, named PICMIs, that are characterized by reduced gene content and are broadly distributed in marine bacteria of the family Vibrionaceae .

Eukaryotic organelle genomes are generally of conserved size and gene content within phylogenetic groups. However, significant variation in genome structure may occur. Here, we report that the Stylonematophyceae red algae contain multipartite circular mitochondrial genomes (i.e., minicircles) which encode one or two genes bounded by a specific cassette and a conserved constant region. These minicircles are visualized using fluorescence microscope and scanning electron microscope, proving the circularity. Mitochondrial gene sets are reduced in these highly divergent mitogenomes. Newly generated chromosome-level nuclear genome assembly of Rhodosorus marinus reveals that most mitochondrial ribosomal subunit genes are transferred to the nuclear genome. Hetero-concatemers that resulted from recombination between minicircles and unique gene inventory that is responsible for mitochondrial genome stability may explain how the transition from typical mitochondrial genome to minicircles occurs. Our results offer inspiration on minicircular organelle genome formation and highlight an extreme case of mitochondrial gene inventory reduction. While the organelle genome is commonly considered to be a single circular DNA molecule, extensive variation exists. Here, the authors report multipartite minicircular genomes in red algae and indicate an origin driven by recombination due to loss of DNA replication, recombination, and repair genes.

A novel nanobody (Nb)-based voltammetric immunosensor coupled with horseradish peroxidase concatemer–modified hybridization chain reaction (HRP-HCR) signal amplifying system is described to realize the rapid and ultrasensitive detection of AFB 1 . To design such an immunoassay, anti-AFB 1 Nbs with smaller molecular size were coated densely onto the surface of Au nanoparticle-tungsten disulfide-multi-walled carbon nanotubes (AuNPs/WS 2 /MWCNTs) functional nanocomposites as an effective molecular recognition element, whereas AFB 1 -streptavidin (AFB 1 -SA) conjugates were ingeniously bound with biotinylated HCR dsDNA nanostructures as the competitor, amplifier, and signal report element. In the presence of AFB 1 targets, a competitive immunoreaction was performed between the analyte and AFB 1 -SA-labeled HCR (AFB 1 -HCR) platform. Upon the addition of SA-modified polyHRP (SA-polyHRP), AFB 1 -HCR nanostructures containing abundant biotins were allowed to cross-link to a quantity of HRP by streptavidin−biotin chemistry for signal amplification and signal conversion. Under optimal conditions, the immunosensor displayed a good linear correlation toward AFB 1 ranging from 0.5 to 10 ng mL −1 with a sensitivity of 2.7 μA • (mL ng −1 ) and an ultralow limit of detection (LOD) of 68 fg mL −1 . The specificity test showed that the AFB 1 immunosensor had no obvious cross-reaction with OTA, DON, ZEN, and FB 1 . The signal of this sensor decreased by 10.18% in 4 weeks indicating satisfactory stability, and its intra- and inter-laboratory reproducibility was 3.42~10.35% and 4.03%~12.11%, respectively. This biosensing system will open up new opportunities for the detection of AFB 1 in food safety and environmental analysis and extend a wide range of applications in the analysis of other small molecules. Graphical abstract

This paper presents a novel strategy for computing mathematical functions with molecular reactions, based on theory from the realm of digital design. It demonstrates how to design chemical reaction networks based on truth tables that specify analog functions, computed by stochastic logic. The theory of stochastic logic entails the use of random streams of zeros and ones to represent probabilistic values. A link is made between the representation of random variables with stochastic logic on the one hand, and the representation of variables in molecular systems as the concentration of molecular species, on the other. Research in stochastic logic has demonstrated that many mathematical functions of interest can be computed with simple circuits built with logic gates. This paper presents a general and efficient methodology for translating mathematical functions computed by stochastic logic circuits into chemical reaction networks. Simulations show that the computation performed by the reaction networks is accurate and robust to variations in the reaction rates, within a log-order constraint. Reaction networks are given that compute functions for applications such as image and signal processing, as well as machine learning: arctan, exponential, Bessel , and sinc. An implementation is proposed with a specific experimental chassis: DNA strand displacement with units called DNA “concatemers”.

Background Cancers exhibit complex transcriptomes with aberrant splicing that induces isoform-level differential expression compared to non-diseased tissues. Transcriptomic profiling using short-read sequencing has utility in providing a cost-effective approach for evaluating isoform expression, although short-read assembly displays limitations in the accurate inference of full-length transcripts. Long-read RNA sequencing (Iso-Seq), using the Pacific Biosciences (PacBio) platform, can overcome such limitations by providing full-length isoform sequence resolution which requires no read assembly and represents native expressed transcripts. A constraint of the Iso-Seq protocol is due to fewer reads output per instrument run, which, as an example, can consequently affect the detection of lowly expressed transcripts. To address these deficiencies, we developed a concatenation workflow, PacBio Full-Length Isoform Concatemer Sequencing (PB_FLIC-Seq), designed to increase the number of unique, sequenced PacBio long-reads thereby improving overall detection of unique isoforms. In addition, we anticipate that the increase in read depth will help improve the detection of moderate to low-level expressed isoforms. Results In sequencing a commercial reference (Spike-In RNA Variants; SIRV) with known isoform complexity we demonstrated a 3.4-fold increase in read output per run and improved SIRV recall when using the PB_FLIC-Seq method compared to the same samples processed with the Iso-Seq protocol. We applied this protocol to a translational cancer case, also demonstrating the utility of the PB_FLIC-Seq method for identifying differential full-length isoform expression in a pediatric diffuse midline glioma compared to its adjacent non-malignant tissue. Our data analysis revealed increased expression of extracellular matrix (ECM) genes within the tumor sample, including an isoform of the Secreted Protein Acidic and Cysteine Rich ( SPARC ) gene that was expressed 11,676-fold higher than in the adjacent non-malignant tissue. Finally, by using the PB_FLIC-Seq method, we detected several cancer-specific novel isoforms. Conclusion This work describes a concatenation-based methodology for increasing the number of sequenced full-length isoform reads on the PacBio platform, yielding improved discovery of expressed isoforms. We applied this workflow to profile the transcriptome of a pediatric diffuse midline glioma and adjacent non-malignant tissue. Our findings of cancer-specific novel isoform expression further highlight the importance of long-read sequencing for characterization of complex tumor transcriptomes.