In molecular biology, small nucleolar RNA derived microRNAs are

microRNA Micro ribonucleic acid (microRNA, miRNA, μRNA) are small, single-stranded, non-coding RNA molecules containing 21–23 nucleotides. Found in plants, animals, and even some viruses, miRNAs are involved in RNA silencing and post-transcr ...

s (miRNA) derived from

small nucleolar RNA In molecular biology, small nucleolar RNAs (snoRNAs) are a class of small RNA molecules that primarily guide chemical modifications of other RNAs, mainly ribosomal RNAs, transfer RNAs and small nuclear RNAs. There are two main classes of snoRNA, t ...

(snoRNA). MicroRNAs are usually derived from precursors known as pre-miRNAs, these pre-miRNAs are recognised and cleaved from a pri-miRNA precursor by the

Pasha Pasha (; ; ) was a high rank in the Ottoman Empire, Ottoman political and military system, typically granted to governors, generals, dignitary, dignitaries, and others. ''Pasha'' was also one of the highest titles in the 20th-century Kingdom of ...

and

Drosha Drosha is a Class 2 ribonuclease III enzyme that in humans is encoded by the ''DROSHA'' (formerly ''RNASEN'') gene. It is the primary nuclease that executes the initiation step of miRNA processing in the nucleus. It works closely with DGCR8 and ...

proteins. However some microRNAs, mirtrons, are known to be derived from

introns An intron is any Nucleic acid sequence, nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e., a region inside a gene."The notion of ...

via a different pathway which bypasses Pasha and Drosha. Some microRNAs are also known to be derived from small nucleolar RNA.

Discovery

Small nucleolar RNA derived microRNA was first described in 2008. The

protozoal Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically, ...

intestinal parasite An intestinal parasite infection is a condition in which a parasite infects the gastro-intestinal tract of humans and other animals. Such parasites can live anywhere in the body, but most prefer the intestinal wall. Routes of exposure and inf ...

Giardia lamblia ''Giardia duodenalis'', also known as ''Giardia intestinalis'' and ''Giardia lamblia'', is a flagellated Parasitism, parasitic protozoan microorganism of the genus ''Giardia'' that colonizes the small intestine, causing a diarrheal condition kn ...

'' lacks the Drosha protein involved in pre-miRNA cleavage from pri-miRNA. However the miRNA processing protein

dicer Dicer, also known as endoribonuclease Dicer or helicase with RNase motif, is an enzyme that in humans is encoded by the gene. Being part of the RNase III family, Dicer cleaves double-stranded RNA (dsRNA) and pre-microRNA (pre-miRNA) into shor ...

is found in ''Giardia''. A 26

nucleotide Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...

RNA, miR2, is processed from the ''Giardia lamblia'' snoRNA GlsR17 by dicer. MiR2 is a microRNA which may regulate the expression of variant surface proteins. Also in 2008, a small RNA was found to be cleaved from SCARNA15, a Human

small Cajal body-specific RNA Small Cajal body-specific RNAs (scaRNAs) are a class of small nucleolar RNAs (snoRNAs) that specifically localise to the Cajal body, a nuclear organelle (cellular sub-organelle) involved in the biogenesis of small nuclear ribonucleoproteins (sn ...

, by Dicer. This small RNA was found to function as a microRNA. Potential microRNAs were also identified in several other Human snoRNAs.

''Giardia'' snoRNA-derived miRNAs

''Giardia lamblia'' produces at least 20 snoRNAs. SnoRNAs guide the modification of

rRNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...

, and contain a region of 10–21 nucleotides which is complementary to the target RNA. Five of the ''Giardia lamblia'' snoRNAs have no complementarities to rRNA, implying that they may have a different function. MicroRNAs are derived from five of the box C/D snoRNAs from ''Giardia lamblia'': *The microRNA miR2 is derived from the snoRNA GlsR17 and may regulate the expression of variant surface proteins *The microRNA miR3 is derived from the snoRNA GlsR16 *The microRNA miR5 is derived from the snoRNA GlsR2. MiR5 may regulate the expression of several different genes, including four

kinases In biochemistry, a kinase () is an enzyme that catalysis, catalyzes the transfer of phosphate groups from High-energy phosphate, high-energy, phosphate-donating molecules to specific Substrate (biochemistry), substrates. This process is known as ...

and three variant surface proteins. The variant surface proteins are different from those potentially regulated by miR2 *The microRNA miR6 is derived from the snoRNA GlsR1. The predicted target sites for this miRNA include variant surface proteins *The microRNA miR10 is derived from the snoRNA GlsR8. The predicted target sites for this miRNA include variant surface proteins

References

{{reflist RNA Non-coding RNA

Discovery

''Giardia'' snoRNA-derived miRNAs

See also

References