Long non-coding RNA: Classification, biogenesis and functions in blood cells.

While there exist some long non-coding RNAs (lncRNAs) that are structurally similar to mRNAs (capped, spliced, poly a tail), not all of the lncRNAs exhibit these features. Structurally, lncRNAs are classified under the regulatory non-coding RNAs category these lncRNA molecules operate as signals, decoys, guides, and scaffolds. In eukaryotes, lncRNAs are transcribed by RNA Polymerase II and RNA Polymerase III at several loci of the genome. Unlike other protein-coding mRNAs, lncRNAs exhibit functional uniqueness by participating in and modulating the various cellular processes such as, histone modification, DNA methylation, and cellular transcription (Wei et al., 2017). LncRNA alters chromatin structure and DNA accessibility, thereby regulating patterns of gene expression (Wang et al., 2011b). Disordered lncRNA with quantitative or qualitative alterations lead to the progression of numerous diseases including blood associated diseases. LncRNAs not only regulate lineage commitment such as cardiovascular lineage but also contribute for the hematopoietic stem cell development with a significant role in myeloid and lymphoid lineage commitment. However, the key molecular functions of lncRNAs in hematopoiesis are still unclear, particularly, their functional role during megakaryocyte development from hematopoietic stem cells (HSCs) is largely unexplored. This review summarizes the current status of knowledge on lncRNAs classification, biogenesis and its role in blood cells.