5. Characteristics of miRNAs
Small non-coding double stranded RNAs
Approximately 19-22 nt long
Repress activity of complementary mRNAs
Regulate 30% of mammalian gene products
1 miRNA = hundreds of mRNAs
“you can change a phenotype by
modulating a single miRNA” Thomas
Wurdinger, HMS
Found in plants, animals, virus.
Many are conserved between vertebrates
and invertebrates
8. History
lin-4, first miRNA to be described in C. elegans; important in
development of the worm from larva to adult.(1993)
let-7, was also described in C. elegans (Reinhard BJ et al, 2000) as
critical to stop the stem-cell-like divisions of seam cells and induce
their fully differentiated state.
1998-Fire and Mello, experiments in C. elegans, first to show that
dsRNA is much more potent at inhibiting gene expression than
antisense RNA. Set the stage for understanding the role of miRNAs
in development and gene regulation.
تاریخچه
11. Biogenesis
• Primary-miRNA is transcribed in the nucleus,
and is usually several kilobases long; posses 5’
cap and a poly-A tail.
• Cleaved in the nucleus by Drocha enzyme to
70nt hairpin transcript (pre-miRNA).
• Transported to the cytoplasm by Exportin 5
through nuclear pores.
• Cleaved by Dicer enzyme (RNase III enzyme)
into 19-22nt ds-transcripts.
• 700 Human genes, 490 mouse genes. 1400
possible human sequences but 733 cloned or
detected. Only ~120 tested.
16. NOMENCLATURE
The prefix “miR” is followed by a dash and a number, the
latter often indicating order of naming.
For example, miR-124 was named and likely discovered prior
to miR-456.
A capitalized “miR-” refers to the mature form of the miRNA,
while the uncapitalized “mir-” refers to the pre-miRNA and
the pri-miRNA.
The “MIR” refers to the gene that encodes them
miRNAS with nearly identical sequences except for one or two
nucleotides are annotated with an additional lower case letter.
نامگذاری
17. NOMENCLATURE
For example, miR-124a is closely related to miR-124b
Species of origin is designated with a three letter prefix.
For example, hsa-miR-124 is a human (Homo sapiens) miRNA and
oar-miR-124 is s sheep (Ovis aries) miRNA.
Other common prefixes include ‘v’ for viral miRNA and ‘d’ for
Drosophila miRNA
Pre-miRNAs, pri-miRNAs and genes that lead to 100% identical
mature miRNAs but that are located at different places in the genome
are indicated with an additional dashnumber suffix
For example, the pri-miRNAs hsa-mir-194-1 and hsa-mir-194-2 lead
to an identical mature miRNA (hsa-miR-194) but are from genes
located in different genome regions.
نامگذاری
18. NOMENCLATURE
When two mature miRNAs originate from the opposite arms of the
same pre-miRNA and are found in roughly similar amounts, they are
denoted with a -3p or -5p suffix.
(In the past it used to be made ’s’ (sense) and ‘as’ (antisense)).
However, the mature miRNA found from one arm of the hairpin is
usually much more abundant than that found from the other arm.
So we use an asterisk following the name indicates the mature
species found at low levels from the opposite arm of the hairpin
For example, miR-124 and miR-124* share a premiRNA hairpin
but much more miR-124 is found in the cell.
نامگذاری
19. Summery of NOMENCLATURE
miR : mature miRNA
miR-124 : discovered prior to miR-456.
miR- : pre-miRNA and the pri-miRNA
MIR : gene that encodes them
miR-124a & miR-124b : nearly identical sequences except for one or two nucleotides
hsa-miR-124 : human (Homo sapiens) miRNA
‘v’ : viral miRNA
‘d’ : Drosophila miRNA
hsa-mir-194-1 : identical mature miRNAs but that are located at different places in the
genome
miR-124*_ : much more miR-124 is found
نامگذاری
40. References
Ana Eulalio, Leon Schulte & Jörg Vogel (2012) The mammalian microRNA response
to bacterial infections, RNA Biology, 9:6, 742-750, DOI: 10.4161/rna.20018
Dong et al., miRNA–Microbiota Interaction in Gut Homeostasis and Colorectal
Cancer, Trends in Cancer (2019), https://doi.org/10.1016/j.trecan.2019.08.003
Mélodie Duvala, Pascale Cossarta, Alice Lebretond,(2017),Mammalian microRNAs
and long noncoding RNAs in the host-bacterial pathogen crosstalk,
www.elsevier.com/locate/semcdb, 2017
خوش مجیدمیرصفا,فرهادسیف,RNAمیکروهایمایعات در ارزشمند بیومارکرهای ،گردشیبیولوژیک
بدن, (1396),مجلهدوره رازی پزشکی علوم24شماره ،160مهر ،11396 ,
منابع