Long noncoding RNA (lincRNA), a new paradigm in gene expression control

Long intergenic non-coding RNAs (lincRNAs) are defined as RNA transcripts that are longer than 200 nucleotides. By definition, these RNAs must not have open reading frames that encode proteins. Many of these transcripts are encoded by RNA polymerase II, are spliced, and are poly-adenylated. This final fact indicates that there is a trove of information about lincRNAs in databases such as the Gene Expression Omnibus (GEO), which is a repository for RNAseq and microarray data. Recent experiments indicate that there are upwards of 15,000 lincRNAs encoded by the human genome. The term "intergenic" refers to the identification of these transcripts from regions of the genome that do not contain protein-encoding genes. These regions coincide with what was once labeled as the "junk DNA" portions of our genomes, which, upon careful examination by whole genome RNA sequencing experiments, clearly encode RNA transcripts. LincRNAs also contain promoter- or enhancer-associated RNAs that are gene proximal and can be either in the sense or antisense orientation, relative to the protein-coding gene with which they are associated. In this review, we describe the functions of lincRNAs playing roles in biological processes such as gene expression control, scaffold formation, and epigenetic control.