Joint single-cell profiling resolves 5mC and 5hmC and reveals their distinct gene regulatory effects [snhmCseq]
Oxidative modification of 5-methylcytosine (5mC) by TET DNA dioxygenases generates 5-hydroxymethylcytosine (5hmC), the most abundant form of oxidized 5mC. Existing single-cell bisulfite sequencing methods cannot resolve  5mC and 5hmC, leaving the cell-type-specific regulatory mechanisms of TET and 5hmC largely unknown. Here we present Joint single-nucleus (hydroxy)methylcytosine sequencing (Joint-snhmC-seq), a scalable and quantitative approach that simultaneously profiles 5hmC and true 5mC in single cells by harnessing differential deaminase activity of APOBEC3A towards 5mC and chemically protected 5hmC. Joint-snhmC-seq profiling of single nuclei from the mouse brains reveals an unprecedented level of epigenetic heterogeneity of both 5hmC and true 5mC at single-cell resolution. We show that cell-type-specific profiles of 5hmC or true 5mC improve multi-modal single-cell data integration, enable accurate identification of neuronal subtypes, and uncover context-specific regulatory effects of cell-type-specific genes by TET enzymes. Overall design: Single-nucleus 5-hydroxymethylcytosine sequencing (snhmC-seq) analysis of adult mouse cortex