Small RNA-seq was performed as described previously (27 (link)). In brief, small RNAs were enriched from 2 μg of total RNA using the Magnetic bead cleanup module (Life Technologies). Libraries were then prepared using the Ion Total RNA-Seq Kit v2 (Life Technologies) and analysed via BioAnalyzer HS Chip (Agilent CA, USA). Afterwards, libraries (18 pM each) were clonally amplified by emulsion PCR in the IonTorrent OneTouch System (Life Technologies) using the Ion PGM Template OT2 200 Kit (Life Technologies) according to manufacturer′s protocol. Sequencing was performed in an IonTorrent Personal Genome Machine using an IonTorrent 316 Chip (Life Technologies).