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Long-read HiPore-C Service: Resolving Complex Structural Variations & V2G

Long-read HiPore-C Service provides high-throughput chromatin conformation capture for identifying multi-way interaction hubs. By integrating Nanopore sequencing with proximity ligation, this RUO service resolves complex structural variations and facilitates enhancer-promoter mapping. It offers significant advantages in genomic scaffolding and multi-contact extraction compared to traditional pairwise short-read sequencing methods.

  • High-Order Interaction Extraction: Identify simultaneous interactions between three or more genomic loci in single molecules.
  • Structural Variation (SV) Resolution: Spanning complex breakpoints and repetitive regions using Nanopore long-read technology.
  • V2G Evidence: Prioritize Variant-to-Gene (V2G) assignments via direct physical evidence of enhancer-promoter hubs.
  • Standardized QC Metrics: Rigorous validation of valid pairs, cis-trans ratios, and interaction multiplicity.
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HiPore-C high-order interaction workflow showing multi-way contacts

Technical Overview of HiPore-C Methodology

Traditional Hi-C methodologies are inherently limited to pairwise interactions, providing a fragmented view of the 3D genome. Our HiPore-C service leverages the capacity of Oxford Nanopore Technologies (ONT) to sequence long DNA concatemers formed during proximity ligation. This allows for the capture of "multi-way contacts," which are essential for understanding how multiple regulatory elements (enhancers, silencers, and insulators) converge on a single promoter to regulate gene expression.

Visualization of high-order chromatin interaction hubs and multi-way contacts

The use of long-reads (typically N50 >15 kb) allows for the direct observation of high-order interactions without the need for computational inference of third-party contacts. This is particularly critical in cancer research, where large-scale rearrangements and structural variations can disrupt normal 3D architecture, leading to oncogene activation.

The Long-Read Advantage

  • Resolve Repetitive Regions: Map interactions in centromeres, telomeres, and segmental duplications.
  • Direct Haplotype Phasing: Assign interactions to specific alleles without complex statistical inference.
  • Complex SV Mapping: Span large insertions, deletions, and inversions to visualize their 3D impact.
  • Reduced Ambiguity: Long reads reduce mapping errors common in short-read Hi-C data.

Detailed HiPore-C Workflow and Bioinformatics Logic

Our standardized RUO workflow is designed to maximize the capture of information-rich concatemers while maintaining the integrity of the original chromatin structure.

1. Sample Preparation and Cross-linking

The process begins with the chemical fixation of cells or tissues using formaldehyde to preserve the in situ 3D organization of DNA-protein complexes. This step ensures that the captured interactions represent biologically relevant spatial proximity rather than random collisions.

2. Enzymatic Digestion (NlaIII or DpnII)

To achieve high resolution, we utilize 4-base cutters such as NlaIII or DpnII. These enzymes provide a high frequency of restriction sites across the genome, allowing for the fine-grained mapping of interactions, even in dense regulatory regions or compact chromatin states.

3. Proximity Ligation and Concatemer Formation

Fragmented DNA is subjected to proximity ligation under dilute conditions. Unlike standard Hi-C, which prioritizes the formation of bi-fragment pairs, HiPore-C promotes the formation of long concatemers consisting of multiple fragments that were physically proximal in the nucleus.

4. Library Construction and Nanopore Sequencing

Proteinase K is used to reverse cross-links, and the resulting multi-fragment DNA is purified. Sequencing libraries are prepared for the PromethION 24/48 platforms to ensure high throughput, typically targeting 50–100 Gb of data per sample to achieve sufficient interaction depth for high-order contact extraction.

5. PPL-Toolbox Analysis Pipeline

Raw Nanopore reads are processed using the PPL-Toolbox (Pore-C Pipeline-Toolbox). This comprehensive pipeline performs several critical tasks: Segmenting (Identifying restriction fragments), Mapping (Aligning to reference genome), Filtering (Removing spurious ligations), and Contact Extraction (Quantifying pairwise and high-order contacts).

HiPore-C assay workflow: Cross-linking, Digestion, Ligation, Nanopore Sequencing, and Analysis

Sample Requirements for HiPore-C Sequencing

Parameter Specification Note
Cell Lines 2 × 106 cells Viability >80% required
Primary Tissue 50–100 mg Flash-frozen in LN2; RUO only
Genomic DNA >5 μg HMW DNA; DIN >7.0
Sequencing Depth 50–100 Gb Depends on genome size/complexity
DNA Fragment Size >30 kb Critical for multi-fragment concatemers

Data-Driven QC: Ensuring Deliverable Reliability

Library Quality Metrics

  • Valid Interaction Multiplicity: We track the distribution of reads containing 2, 3, 4, or 5+ fragments. High-quality libraries show a significant proportion of 3rd-order and higher contacts.
  • Cis-to-Trans Ratio: An indicator of library noise. Intra-chromosomal (cis) interactions should significantly outweigh inter-chromosomal (trans) interactions to confirm biological signal.

Interaction Specificity

  • P(s) Contact Probability: Assessment of how contact frequency decays with genomic distance, used to verify the capture of local chromatin loops and TADs.
  • FRiP (Fraction of Reads in Peaks): Measures the enrichment of interaction signals within known regulatory regions or called loops.

High-Order Interaction Discovery in Complex Genomes

Enhancer Hubs and V2G Mapping

In many biological contexts, multiple enhancers coordinate to regulate a single gene. HiPore-C directly captures these clusters, known as "enhancer hubs," providing evidence of which distal elements are physically interacting with a target promoter at the same time. This is a critical tool for V2G & Enhancer Assignment projects in pharmaceutical discovery where prioritizing variants is paramount.

Resolving Complex Structural Variations (SVs)

Short-read Hi-C often fails to map interactions accurately across large structural variations, such as inversions or complex translocations in cancer genomes. The long-read nature of HiPore-C allows individual concatemers to span across breakpoints, providing a clear map of how SVs alter the local and global 3D architecture.

Aneuploidy and Haplotype Phasing

Using the single-molecule resolution of HiPore-C, researchers can resolve interactions for specific alleles. This is particularly useful for studying genomic imprinting, X-chromosome inactivation, or the effects of heterozygous variants on 3D looping in polyploid or cancerous genomes.

Case Study: Mapping Single-Allele Topology and Enhancer Hubs in Cancer

Investigators aimed to resolve the complex regulatory landscape of the beta-globin locus, focusing on how the Locus Control Region (LCR) interacts with multiple genes simultaneously in a single-allele context. The study utilized a high-throughput long-read chromatin conformation capture approach to overcome the limitations of pairwise mapping.

The team utilized HiPore-C sequencing and the PPL-Toolbox analysis pipeline to process the data. Key steps included formaldehyde cross-linking, NlaIII digestion, and proximity ligation followed by sequencing on the PromethION platform to generate multi-kb concatemers.

The analysis identified interaction clusters where the LCR was in physical contact with two or more globin genes simultaneously. Visualization of multi-way interaction clusters at the beta-globin locus (Source: PMC9988853, Fig 3) demonstrated that high-order hubs are a primary feature of this locus's regulation. The data showed that high-order interactions occur at a higher frequency than would be predicted by a pairwise-only model.

HiPore-C genomic track visualization of multi-way interaction clusters

HiPore-C data successfully resolved the "enhancer hub" at the beta-globin locus, providing a blueprint for applying this technology to other complex V2G and disease-related loci. This case confirms the necessity of long-read approaches for resolving cooperative regulatory mechanisms.

Advanced Applications and Analysis Deliverables

V2G Prioritization Reports
Identification of high-confidence enhancer-promoter assignments based on multi-way contact evidence.

TAD and Loop Calling
Standardized 3D genome architecture analysis using processed Pore-C data.

SV Breakpoint Analysis
High-resolution mapping of structural variations and their impact on the surrounding 3D environment.

Interactive Visualizations
Files compatible with Juicebox, HiGlass, and other 3D genomics browsers for seamless exploration.

Explore our related advanced technologies, including specialized Pore-C service for general epigenetic research, standard HiC sequencing for budget-sensitive pairwise mapping, and Capture-C options for targeted locus refinement.

Frequently Asked Questions

References

  1. Deshpande et al. (2023). High-throughput Pore-C reveals enhancer hubs. Nature Communications.
  2. Wang et al. (2025). Pore-C Pipeline-Toolbox: a comprehensive pipeline. Briefings in Bioinformatics.
  3. Nanopore 3D Genomics Technical Standards. (2024). Standardized QC and Deliverables for RUO Services.
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