Table 2.
Description of ncRNA and its biogenesis
| Type of RNA | Full_form | Biogenesis description | Functions | References |
|---|---|---|---|---|
| miRNA | microRNA | Biogenesis of miRNAs begins with DNA sequences known as miRNA genes or clusters of genes that are only transcripted as miRNA molecules or collectively as polycistronic transcripts. MiRNAs can also be found in an intron or untranslated region (UTR) of a protein-coding gene | miRNA plays a vital role in post-transcriptional gene regulation. By inhibiting translation and destabilizing mRNA, miRNAs regulate their targets in eukaryotic cells | Annese et al. 2020 |
| lncRNA | Long non-coding RNA | lncRNAs are RNA-type molecules with a 5′ methyl-cytosine cap and a 3′ poly(A) tail transcribed by RNA polymerase II (Pol II). 31 LncRNAs are categorized into many different categories based on their various features. lncRNAs, for example, can be classified into five categories based on their genetic origins: sense, antisense, bidirectional, intronic, and intergenic. LncRNAs are categorized into three categories based on their function: rRNA, tRNA, and cRNA | A new class of epigenetic regulators called lncRNAs is crucial to regulating epigenetic processes. LncRNAs modulate histone or DNA modification, primarily methylation, and acetylation, to control epigenetic modification primarily in the nucleus, which controls gene transcription at the transcriptional level | Liu et al. 2021a, b |
| snRNA | Small nuclear RNA | snRNA can be transcribed from a promotor (similar to mRNA) and encoded within intronic sequences | Splicing of introns from primary genomic transcripts is a critical function of small nuclear RNAs | Matera et al. 2007 |
| snoRNA | Small nucleolar RNA | Except for a tiny subset of snoRNAs that RNA polymerase II transcriptions autonomously, most snoRNAs in vertebrates are encoded in the introns of protein-coding or non-coding genes. Most intronic snoRNAs are produced through co-transcription with the host gene, splicing, debranching of the intron lariat, and nucleoplasmic exonucleolytic digestion. The maturation of snoRNAs, which is co-transcriptionally induced, depends on the recruitment of ribonucleoproteins to the nascent intronic snoRNAs. Additional SnoRNPs are sent to Cajal bodies, carrying out additional maturation and processing operations. Shq1, Naf1, and NUFLP are additional auxiliary elements that contribute to snoRNP assembly and maturation. Both processing stability and nucleolar localization depend on these proteins | The function of snoRNA is to participate in rRNA processing, regulation of mRNA processing, involvement in stress response, and metabolic changes. snoRNA has a more and influential role in cancer | Liang et al. 2019 |
| siRNA | Small interfering RNA | The cascade leading to the synthesis of mature siRNA begins with transcription by RNA polymerase II (in mammals), RNA polymerase III (from an shRNA template), or RNA polymerase IV (in plants), creating double-stranded RNA (dsRNA) (dsRNA) | siRNA is frequently employed in molecular biology to silence desired genes temporarily. Upon binding to their target transcript, they trigger RNAi based on the complementarity of their sequences | Carthew and Sontheimer 2009 |
| piRNA | PIWI-interacting RNA | Lengthy RNA precursors are transcribed in the nucleus and exported into the cytoplasm. In the cytoplasm, piRNA precursors are further processed to form mature piRNAs that get loaded into Piwi proteins | piRNA has essential roles in embryonic development, the preservation of germline DNA integrity, the generation of heterochromatin, the silencing of transposon transcription, the suppression of translation, and the epigenetic regulation of sex determination | Wu et al. 2020a, b |
| circRNA | Circular RNA | CircRNAs often result from exon or intron circularization and splicing activities. Exonic circRNAs can be produced by a procedure known as back splicing, dependent on spliceosomal splicing. Exons are spliced in the opposite direction by combining an upstream and a downstream 3′ and 5′ splice site, resulting in a circular product. Exon skipping, which creates a lariat structure containing exons and introns, is another method that leads to exonic circRNAs. The intron is cut out of this precursor during self-splicing, and the lariat is circularized | CircRNAs control target gene expression by inhibiting miRNA activity as a miRNA sponge. Through several miRNA binding sites, one circRNA can control one or more miRNAs | Beermann et al. 2016 |