RNA was isolated using the MagMAX™-96 for Microarrays Total RNA Isolation Kit (Thermo Fisher Scientific, #AM1839) per manufacturer's instructions.  RNA concentration was determined using a NanoDrop 8000 (ThermoFisher Scientific, Waltham, MA). Paired-end sample libraries consisting of 60 bp with 6 nucleotide indices were prepared for measuring high-throughput 3' digital gene expression based on a previously published protocol (Massachusetts Institute of Technology, Cambridge, MA) (Soumillon, 2014).