Small RNA

Small RNA (sRNA) are polymeric RNA molecules that are less than 200 nucleotides in length, and are usually non-coding.^[1] RNA silencing is often a function of these molecules, with the most common and well-studied example being RNA interference (RNAi), in which endogenously (from within the organism) expressed microRNA (miRNA) or endogenously/exogenously (from outside the organism) derived small interfering RNA (siRNA) induces the degradation of complementary messenger RNA.^[2] Other classes of small RNA have been identified, including piwi-interacting RNA (piRNA) and its subspecies repeat associated small interfering RNA (rasiRNA).^[3] Small RNA "is unable to induce RNAi alone, and to accomplish the task it must form the core of the RNA–protein complex termed the RNA-induced silencing complex (RISC), specifically with Argonaute protein".^[4]: 366

Small RNA have been detected or sequenced using a range of techniques, including directly by MicroRNA sequencing on several sequencing platforms,^[5][6][7] or indirectly through genome sequencing and analysis.^[8] Identification of miRNAs has been evaluated in detecting human disease, such as breast cancer.^[6] Peripheral blood mononuclear cell (PBMC) miRNA expression has been studied as potential biomarker for different neurological disorders such as Parkinson's disease,^[9] Multiple sclerosis.^[10] Evaluating small RNA is useful for certain kinds of study because its molecules "do not need to be fragmented prior to library preparation".^[4]: 162