library_construction_protocol: FACS sorted cells were resuspended in QIAzol for RNA-extraction following the manufacturer's protocol for the miRNeasy micro kit (Qiagen #217084), including the on-column DNase digestion (Qiagen #79256). A minimum of 10 ng of total RNA was used for sequencing libraries following Illumina's TruSeq RNA v2 protocol (Illumina #RS-122-2001). Libraries were sequenced on an Illumina NextSeq 500.