miRNAs in Gene Expression

miRNAs in Gene Expression

miRNAs are naturally occurring in animal and plant organisms. They are highly conserved and play an important role in gene regulation, especially in gene silencing. They have an important function in cell differentiation and dedifferentiation, for example in female fertility and preimplantation development. miRNAs are important for the balance between pluripotency and differentiation in the embryo and in embryonic stem cells. For the future, the use of miRNAs together with exosomes promises new biomarkers and treatment approaches of infertility or degenerative diseases. (Virant-Klun, Ståhlberg et al. 1). Dysregulation of the expression of miRNAs is said to be involved in the development of various types of cancer, such as ovarian cancer and insulin regulation (Chakraborty et al. 2).

microRNAs (miRNAs) are non-coding small RNA molecules that are encoded on separate genes. The size varies in the literature from 17 to 27 bp in length. It has been shown that a large number of protein-coding genes are regulated by miRNAs.

microRNAs were first described in 1993 by means of lin-4 miRNA in C. elegans by Lee et al 3. In a publicly available microRNA database, all published miRNA sequences as well as comments and explanations can be retrieved (miRBase, currently more than 28000 entries 4).

In contrast to siRNA, miRNA is encoded in the cell on its own pri-miRNA genes (primary microRNA). They are transcribed, resulting in a so-called pri-miRNA which forms a hairpin structure. A microprocessor complex (binding protein and Drosha = RNase III) converts the pri-miRNA into a pre-miRNA. In the cytoplasm, the enzyme Dicer cuts the double-stranded hairpin structure of the pre-miRNA into small individual parts (ds-miRNA), which are subsequently separated into single strands (mature miRNA).

miRNAs regulate the expression of mRNA. They bind at the 3 'end (3'-UTR = untranslated region) of the complementary mRNA sequence. This results in a suppression of the translation of the target mRNA with subsequent gene silencing. If the binding sequences are only partially identical, the translation of certain genes is only reduced but not completely inhibited.

The investigation of the expression of miRNA is normally carried out by reverse transcription of the RNA into cDNA and the subsequent quantification with quantitative RealTime PCR (qPCR). An alternative are new, special Microarray platforms or Rolling Circle Amplification (RCA).

For the purification of your miRNA from cells and tissue Genaxxon offers a miRNA Purification Kit.

1 Virant-Klun et al.: MicroRNAs: From Female Fertility, Germ Cells, and Stem Cells to Cancer in Humans. In: Stem Cells Int. 2016;2016:3984937. doi: 10.1155/2016/3984937. Epub 2015 Nov 9. PMID 26664407

2 Chakraborty et al.: Influence of miRNA in insulin signaling pathway and insulin resistance: micro-molecules with a major role in type-2 diabetes.  In: Wiley Interdiscip Rev RNA. 2014 Sep-Oct;5(5):697-712. doi: 10.1002/wrna.1240. Epub 2014 Jun 18. PMID 24944010

3 Lee et al.: The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14. In: Cell. 75(5), 1993, S. 843–854, PMID 8252621

4 http://www.mirbase.org/index.shtml

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