library_construction_protocol: RNA was extracted using TRI Reagent and Direct–zol RNA microprep kit (both Zymo) including on-column DNase digestion to remove genomic DNA. Samples were quantified using an Agilent 2100 Bioanalyzer and passed QC. Library preparation was done using a TruSeq RNA v2 kit (Illumina) and sequencing with NextSeq 500 instrument (Illumina) by Northwestern's NuSeq core facility, generating ~40 million single-end 75 bp reads for each sample