RNA was harvested using TRIzol. For input samples, small RNAs less than 300 nt were purified on an acrylamide gel. For biotin samples, RNAs were reacted with DBCO-PEG4-biotin and purified using streptavidin beads. For WGA samples, RNAs were purified using WGA beads. For PNG samples, purfiied RNAs were digested with PNGase F. Small RNA libraries were prepared according to procedures in Illumina TruSeq small RNA library kit.