For construction of sequencing libraries, we used an Ovation Single Cell RNA-Seq System (NuGEN, West Cumbria, UK). Briefly, first-strand cDNAs were selectively synthesized from the purified RNAs using proprietary whole-transcriptome primers for nonribosomal RNAs. Second-strand cDNAs were then synthesized from the first-strand cDNAs using the second-strand primer. After ligation of the reverse adaptor, libraries were enriched by polymerase chain reaction (PCR). Quality checks of the libraries were carried out using a Bioanalyzer (Agilent Technologies; Santa Clara, CA, USA).