RNA was isolated (RNeasy Mini Kit; QIAGEN, Cat no. 74104) and given on-column DNase treatment (RNase-Free DNase Set; QIAGEN) for 15 min. The removal of genomic DNA was ascertained by an additional treatment of the samples with DNase I (Invitrogen, Cat no. 18068-015). RNA was eluted in dH2O. RNA libraries were prepared for sequencing using standard Illumina protocols