Nat. Rev. Gastroenterol. Hepatol. doi:10.1038/nrgastro.2017.169 Figure 3 Classification of long non-coding RNAs according to their genomic origin Figure 3 | Classification of long non-coding RNAs according to their genomic origin. Intergenic long non-coding RNAs (lncRNAs) such as long intervening non-coding RNAs (lincRNAs) and many pseudogenes are transcribed in the intergenic region between two protein-coding genes. Intronic lncRNAs are lncRNAs arising from intronic regions within protein-coding genes. Antisense lncRNA are lncRNAs transcribed in the antisense direction of overlapping protein-coding genes. Bidirectional lncRNAs such as promoter upstream transcripts (PROMPTs) are transcribed in the promoter regions of protein-coding genes in a bidirectional manner. Enhancer lncRNAs are lncRNAs transcribed from the enhancer regions of protein-coding genes. Some precursor mRNAs (pre-mRNAs) are back-spliced to create circular RNAs (circRNAs), which are also regarded as lncRNAs. Wong, C.-M. et al. (2018) Non-coding RNAs in hepatocellular carcinoma: molecular functions and pathological implications Nat. Rev. Gastroenterol. Hepatol. doi:10.1038/nrgastro.2017.169