In molecular biology, small nucleolar RNA derived microRNAs are microRNAs (miRNA) derived from small nucleolar RNA (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 and Drosha proteins. However some microRNAs, mirtrons, are known to be derived from introns 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 intestinal parasite "Giardia lamblia" lacks the Drosha protein involved in pre-miRNA cleavage from pri-miRNA. However the miRNA processing protein dicer is found in "Giardia". A 26 nucleotide 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, 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, 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":
References.
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