Fig. 1

Schematic representation of lncRNA species and structures. a LncRNAs transcribed from functional DNA element regions: promoter upstream transcript (PROMPTs), enhancer-associated RNA(eRNAs); (b) Mainstream five categories based on genomic location and transcript orientation of lncRNA: (1) sense lncRNAs and (2) antisense lncRNAs, overlapping and transcribed from the same or opposite strand of protein-coding genes, (3) bidirectional lncRNAs, typically transcribed in the opposite direction of its neighboring protein-coding gene (less than 1 kb away) [13], (4) intronic lncRNAs, transcribed entirely from introns [14], (5) intergenic lncRNAs (lincRNAs), transcribed from genomic interval [1]; (c, d) LncRNAs characterized by snoRNA caps: Sno-lncRNAs have snoRNA caps at both ends, while SPA-lncRNAs possess 5’ snoRNA only; (e) LncRNAs characterized by tRNA-like extremities, with the 3′ end alternatively processed by ribonuclease P (RNase P), e.g., MALAT1 and NEAT1_2; (f, g) LncRNAs with close circular structures: derived from back-splicing of exons named circular RNAs, and ciRNAs are produced from intron lariats.