The Diversity of Long Noncoding RNAs and Their Generation.

Long noncoding RNAs (lncRNAs) are emerging as potential key regulators in gene expression networks and exhibit a surprising range of shapes and sizes. Several distinct classes of lncRNAs are transcribed from different DNA elements, including promoters, enhancers, and intergenic regions in eukaryotic genomes. Additionally, others are derived from long primary transcripts with noncanonical RNA processing pathways, generating new RNA species with unexpected formats. These lncRNAs can be processed by several mechanisms, including ribonuclease P (RNase P) cleavage to generate mature 3' ends, capping by small nucleolar RNA (snoRNA)-protein (snoRNP) complexes at their ends, or the formation of circular structures. Here we review current knowledge on lncRNAs and highlight the most recent discoveries of the underlying mechanisms related to their formation.