RNA was then extracted following the protocol of the Direct-zol TM RNA Miniprep TRIzol In. RNA Out kit (Zymo Reasearch, California). The extracted RNA was then treated twice with DNaseI using the TURBO DNA-freeTM Kit (Invitrogen by Thermo Fisher Scientific, Lithuania) to remove possible traces of DNA. Zymo-Seq RiboFree Total RNA library preparation kit (Zymo Research Corp., Irvine, CA) has been used for library preparation (library type: fr-firststrand).