Fig. 2

Classification of lncRNAs. Multiple type of lncRNAs have been identified, including (1) Sense lncRNA: transcribed from the sense strand of a protein coding gene; (2) Antisense lncRNA: transcribed from the antisense strand of a protein coding gene, usually overlapping the introns or exons of the sense strand; (3) Intergenic lncRNA: transcribed from the space between two protein coding genes; (4) Intronic lncRNA: incorporated inside of the introns of protein coding genes; (5) Bidirectional lncRNA: transcribed in an opposite direction with respect to the nearby protein coding gene and located within 1 kb of the promoter of the protein coding gene [8, 38]