Fig. 3.

Schematic diagram illustrating the origin of long non-coding transcripts based on their biogenesis. lncRNAs can be classified on the basis of their proximity to protein coding genes (PCGs) as (a) exon sense & intron sense (which overlaps the sense strand of PCG), (b) natural antisense (which overlaps the antisense strand of PCG), (c) intronic antisense (which is derived entirely from or within an intron of another transcript), (d) intergenic (which is not located near any other protein coding loci), and (e) bidirectional (which have transcription start sites in close proximity to a PCG but are transcribed in the opposite direction) [21].