library_construction_protocol: Cells were dissociated by papain, filtered and kept on ice until FACS sorting. Sorted cells were collected into ice cold PBS 1X, and immediately pelleted by centrifugation (500 rcf, 5 minutes, 4°C).  Total RNA was extracted by NORGEN Single Cell RNA Purification Kit (NORGEN, 51800) with genomic DNA digestion using RNase-Free DNase Ⅰ Kit (NORGEN, 25710) according to manufacturer's protocol.  Sequencing of total RNA was done by Ovation SoLo RNA-seq System (NuGEN, 0501-32), using 2.5 – 5ng of RNA as an input according to manufacturer's protocol.