Modular oxidation of cytosine modifications and their application in direct and quantitative sequencing of 5-hydroxymethylcytosine

Selective, efficient, and controllable oxidation of cytosine modifications is valuable for epigenetic analyses, yet only limited progress has been made. Here, we present two modular chemical oxidation reactions: conversion of 5-hydroxymethylcytosine (5hmC) into 5-formylcytosine (5fC) utilizing 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (ACT+ BF4–) and further transformation of 5fC into 5-carboxycytosine (5caC) through Pinnick oxidation. Both reactions are mild and efficient on double-stranded DNA. We integrated these two oxidations with borane reduction to develop chemical-assisted pyridine borane sequencing plus (CAPS+), for direct and quantitative mapping of 5hmC. Compared with chemical-assisted pyridine borane sequencing (CAPS), CAPS+ improved the conversion rate and false-positive rate. We applied CAPS+ to mouse embryonic stem cells (mESCs) DNA, human normal brain and glioblastoma DNA samples, and demonstrated its superior sensitivity in analyzing the hydroxymethylome Overall design: Whole genome sequencing of 5 hydroxymethylcytosine applying CAPS+ in mESCs (two replicates) and human brain samples (normal brain and glioblastoma).