Decoding the regulatory genome: single-cell four-omics integration
In a recent study published in Nature, Chen et al. introduced CHARM (single-cell assay for Chromatin conformation, Histone modi fi cation, chromatin Accessibility, and RNA expression Multi-omics pro fi ling), a platform that simultaneously captures four regulatory modalities within the same nucleus. 1 This integrated strategy provides a comprehensive framework for dissecting how multiple layers of epigenetic regulation converge to control gene expression at single-cell resolution. Gene regulation in eukaryotic cells is governed by a complex interplay of molecular and spatial mechanisms. Chromatin accessibility determines whether regulatory elements such as promoters and enhancers are available for transcription factor binding. Histone modi fi cations de fi ne chromatin states that either promote or repress transcription. In parallel, the three-dimensional organization of the genome establishes spatial proximity between distal regulatory elements and their target genes. Although each of these regulatory layers has been extensively studied, understanding how they operate together within the same cell has remained a major challenge. 2 Previous technologies have provided valuable insights into individual modalities. ATAC-seq pro fi les chromatin accessibility, CUT&Tag captures histone modi fi cations, and Hi-C reveals three-dimensional genome architecture. Recent single-cell platforms such as ChAIR and scHiCAR jointly pro fi le chromatin accessibility, RNA, and 3D contacts, but their 3D contact capture is anchored at accessible chromatin or candidate cis-regulatory elements, introducing structural bias into chromatin architecture reconstruction. 3,4 Moreover, regulatory modalities not captured by these platforms, such as histone modi fi cations, require separate pro fi ling and computational integration for broader cross-modality analysis. CHARM is distinguished from previous platforms by adding histone modi fi cation as a fourth same-cell modality and by using restriction-enzyme-based Hi-C