library_construction_protocol: Cells were sorted directly into Trizol LS. Extraction was performed using Rneasy mini kit (Qiagen) per manufacturer's instructions. Total RNA underwent amplification using the SMART-seq V4 (Clonetech) ultralow input RNA kit for sequencing (12 cycles of amplification for 2-10 ng of total RNA). Subsequently, 10 ng of amplified cDNA was used to prepare Illumina Hiseq libraries with the Kapa DNA library preparation chemistry (Kapa Biosystems) using 8 cycles of PCR. Samples were barcoded and run on a Hiseq 4000, in a 50bp/50bp paired-end run, using the TruSeq SBS Kit v3 (Illumina).