Assay for Transposase-Accessible Chromatin Using Sequencing of Freshly Isolated Muscle Stem Cells

Actively transcribed genes harbor cis-regulatory modules with comparatively low nucleosome occupancy and few high-order structures (="open chromatin"), whereas non-transcribed genes are characterized by high nucleosome density and extensive interactions between nucleosomes (="closed chromatin"), preventing transcription factor binding. Knowledge about chromatin accessibility is crucial to understand gene regulatory networks determining cellular decisions. Several techniques are available to map chromatin accessibility, among which the Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq) is one of the most popular. ATAC-seq is based on a straightforward and robust protocol but requires adjustments for different cell types. Here, we describe an optimized protocol for ATAC-seq of freshly isolated murine muscle stem cells. We provide details for the isolation of MuSC, tagmentation, library amplification, double-sided SPRI bead cleanup, and library quality assessment and give recommendations for sequencing parameters and downstream analysis. The protocol should facilitate generation of high-quality data sets of chromatin accessibility in MuSCs, even for newcomers to the field.