snoRNAs are a type of non-coding RNA that is split into two groups CD box snoRNAs and HACA box snoRNAs. 2'-O-ribose methylation and pseudouridylation of ribosomal RNAs (rRNAs) are the canonical functions of CD box and HACA box snoRNAs, respectively. New evidence suggests that snoRNAs have a role in a variety of physiological and pathological cellular processes. snoRNA mutations and abnormal expression have been found in cell transformation, carcinogenesis, and metastasis, suggesting that snoRNAs could be used as cancer biomarkers andor therapeutic targets. As a result, more research into the functions and mechanisms of snoRNAs is necessary.
Biogenesis of snoRNAs
Except for a tiny number of snoRNAs transcribed independently by RNA polymerase II, most snoRNAs are encoded in the introns of protein-coding or non-coding genes in vertebrates. Cotranscription with the host gene, splicing, debranching of the intron lariat, and exonucleolytic digestion in the nucleoplasm are all steps in the synthesis of most intronic snoRNAs. The maturation of snoRNAs requires the recruitment of ribonucleoproteins to nascent intronic snoRNAs, which is begun by cotranscription. Both processing stability and nucleolar localization rely on these proteins. Many auxiliary elements, such as Shq1, Naf1, and NUFLP, are also involved in snoRNP formation and maturation. SnoRNPs are transferred to Cajal bodies, where they undergo further maturation and processing. They are then transported to the nucleolus.
Functions of snoRNAs
The role of snoRNAs in the modification, maturation, and stabilization of rRNA is one of their most well-studied functions. Hundreds of 2′-O-methylation or pseudouridylation residues have been discovered inside conserved and functional areas of rRNAs as the research progresses. A region upstream of box D andor box D' detects target RNAs, causing the methylase fibrillarin to 2′-O-methylate the fifth NT. Dyskerin is responsible for the conversion of uridines to pseudouridine, and the location for pseudouridylation is 14–16 NTs upstream of box H andor box ACA.
Recent data suggest that snoRNAs play a crucial role in gene expression regulation. The imprinted SNURF–SNRPN locus on the human chromosome, which is frequently lost in Prader–Willi syndrome, encodes SNORD115 (PWS). snoRNAs can act as miRNAs as well. Human ACA45 has been proven to be a genuine snoRNA that can be processed into a mature miRNA of 21 nucleotides by the RNAse III family endoribonuclease dicer. mmu-miR-1839 was the initial name for this snoRNA product, and it was shown to be processed separately from the other miRNA-generating endoribonuclease drosha. Putatively snoRNA-derived miRNA-like fragments have been found in a variety of species, according to bioinformatic investigations.
snoRNA profiling using small RNA sequencing
Figure 1. Profiling of small nucleolar RNAs by next generation sequencing. (Krishnan, 2016)
MicroRNA (miRNA), small interfering RNA (siRNA), and piwi-interacting RNA (piRNA) are examples of small RNA species, as are other types of small RNA such as small nucleolar RNA (snoRNA) and small nuclear RNA (snRNA). NGS can detect weakly expressed short RNAs and reveal length and sequence heterogeneity quantitatively. Without the need for available reference genomes, NGS is a useful method for exploring the function of short RNAs and predicting possible mRNA target molecules. The separation of small RNAs from total RNA using gel electrophoresis selection or silica spin columns is the first step in creating a high-quality small RNA sequencing library. Small RNAs are reverse transcribed, amplified by PCR, and sequenced after RNA adapter ligation using a 5' adenylated DNA adapter with a blocked 3'end. Sequencing reads can be mapped to a species-specific database, such as mirWalk or miRBase, to detect and characterize known miRNAs.
References:
Liang J, Wen J, Huang Z, et al. Small nucleolar RNAs: insight into their function in cancer. Frontiers in oncology. 2019 Jul 9;9:587.
Krishnan P, Ghosh S, Wang B, et al. Profiling of small nucleolar RNAs by next generation sequencing: potential new players for breast cancer prognosis. PloS one. 2016 Sep 15;11(9).
Kiss T. Small nucleolar RNAs: an abundant group of noncoding RNAs with diverse cellular functions. Cell. 2002 Apr 19;109(2).
* For Research Use Only. Not for use in diagnostic procedures.
Figure 1. Profiling of small nucleolar RNAs by next generation sequencing. (Krishnan, 2016)
