Pairwise Proximity-Differentiated Visualization of Single-Cell DNA Epigenetic Marks.

Spatial positioning and proximity of relevant biomolecules such as DNA epigenetic marks are fundamental to a deeper understanding of life. However, it remains poorly explored and technically challenging. Here we report the pairwise proximity-differentiated visualization of single-cell 5-formylcytosine (5fC) and 5-hydroxymethylcytosine (5hmC). These two marks on chromatin in fixed cells are successively labeled and crosslinked with their DNA primer probes via click chemistry. Based on a pairwise proximity-differentiated mechanism, proximal 5fC/5hmC sites and residual 5fC or 5hmC sites are encoded with respective circularized barcodes. These barcodes are simultaneously amplified for multiplexed single-molecule imaging. We thus demonstrate the differentiated visualization of 5fC or 5hmC spatial positioning and their pairwise proximity in single cells. Such multi-level subcellular information may provide insights into regulation functions and mechanisms of chromatin modifications, and the spatial proximity can expose the potential crosstalk or interaction between their reader proteins.