lncRNAs were first found in rat full-length cDNA sequence libraries, usually overlapping or dispersed between transcripts. According to location and context, lncRNA can be divided into five categories, including inter-gene long-chain non-coding RNA (intergenic lncRNA, also known as long intergenic ncRNA or lincRNA, which is produced by the transcription of spacer sequences between genes encoded in the genome), intron long-chain non-coding RNA (intronic lncRNA, which is completely transcribed from introns within a protein-coding gene), sense long-chain non-coding RNA (sense lncRNA, transcribed from the coding strand of a protein-coding gene and partly or completely overlapping the gene exons), antisense long-chain non-coding RNA (antisense lncRNA, transcribed from the non-coding strand of a gene), and bidirectional long-chain non-coding RNA (bidirectional lncRNA, transcribed from the promoter region in two opposite directions) (Table 2).8, 9Table 2Classification of lncRNAsClassificationDescriptionExampleIntergenicproduced by the transcription of spacer sequences between genes encoded in the genomeXIST, TMEM161B-AS, HAR1, NEAT1, TUG1Intronictranscribed from introns within a protein-coding geneLnc-OR51B4-3, KCNIP4-IT1Sensetranscribed from the coding strand of a protein-coding gene and partly or completely overlapping the gene exonsSNHG4Antisensetranscribed from the non-coding strand of a geneBACE1-AS, MALAT1, lnc-LRR1, TUSC7Bidirectionaltranscribed from the promoter region in two opposite directionsHoxa11as, IGF2AS, HOTAIRM1