library_construction_protocol: Cells were isolated from skeletal muscle Total RNA was isolated from freshly-sorted satellite cells with the PicoPure RNA Isolation Kit (KIT0204), NEBNext Single Cell/Low Input RNA Library Prep Kit was used for library preparation. Cells were processed for RNA extraction right after sorting. Total RNA was extracted with the Arcturus PicoPure RNA Isolation Kit (Thermo Fisher) together with on-column DNA digestion. Both RNA isolation kits were used according to the manufacturer's instructions. RNA concentration was measured with NanoDrop 2000/2000c (Thermo Fisher). RNA integrity and library preparation were checked with a BioAnalyzer (RNA Pico Chip, Agilent). For the in vitro-based RNA-Seq, low input library preparation and single-end sequencing was performed in the Centre de Regulació Genomica (CRG) genomics unit using the HiSeqTM Sequencing Kit and the TruSeq v3 Cluster (Illumina). For the RNA-seq experiment in freshly isolated cells standard Directional RNA-seq library preparation and single-end sequencing (Illumina HiSeq 2500) was performed in the Genomic Unit of Centro Nacional de Investigaciones Cardiovasculares (CNIC).