Introduction• MiRNAs are non-coding RNAs found only in eukaryotic cells.• Small in size with an average length of 22 nucleotides.• Transcribed by RNA polymerase II from independent genes or introns of protein-coding genes• They play important gene-regulatory roles in both plants and animals.• The first miRNA (lin-4) was discovered in C.elegans in the year 1993.
BiogenesisSource :- The Role of MicroRNAs in Cholesterol Efflux and Hepatic Lipid Metabolism by Kathryn J. Moore, Katey J. Rayner, YajairaSu arez, and Carlos Fern andez-Hernando
Functions of miRNAs Gene silencing in plants and animals Ribosome mRNASource :- The widespread regulation of microRNA biogenesis, function and decay by Jacek Krol, IngaLoedige and Witold Filipowicz.
Functions of miRNAsTumor suppression and oncogenes-• About 50% of the annotated human miRNAs map within fragile sites of chromosomes, which are areas of the genome that are associated with various human cancers.• Recent evidence indicates that miRNAs can function as tumour suppressors and oncogenes, and they are therefore referred to as ‘oncomirs’.• Gene therapies that use miRNAs might be an effective approach to blocking tumour progression. miRNAs such as let-7, which has been shown to negatively regulate the Ras oncogenes, and miR- 15 and miR-16, which negatively regulate BCL2, are promising candidates for cancer treatment.
Source :- Oncomirs — microRNAs with a role in cancer by Aurora Esquela-Kerscher and Frank J. Slack
Functions of miRNAs Developmental SwitchesSource :- microRNA Functions by Natascha Bushati and Stephen M. Cohen
Functions of miRNAsThresholdingDI- DeltaN- NotchSu(H)- suppressor of HairlessE(spl)- enhancer of SplitSens- senselessSource :- MicroRNA-9a ensures theprecise specification of sensory organprecursors in Drosophila by Yan Li, FayWang, Jin-A Lee, et al.
Regulation of miRNAsThe need :-• Many miRNAs are expressed in a tissue-specific or developmental stage- specific manner, thereby greatly contributing to cell-type- specific profiles of protein expression.• With the potential to target dozens or even hundreds of different mRNAs, individual miRNAs can coordinate or fine-tune the expression of proteins in a cell.• These considerations call for a tight and dynamic regulation of miRNA levels and activity, particularly during rapid developmental transitions or changes in cellular environment.
Regulation of miRNAsRegulation of transcriptionStimulates expression of miR-34 and miR-107 which enhancescell cycle arrest and apoptosis Stimulates expression of oncogenic miRNAs but inhibits expression of tumor suppressor miRNAsSource :- The widespread regulation of microRNA biogenesis, function and decay by Jacek Krol, IngaLoedige and Witold Filipowicz.
Regulation of miRNAsRegulation of processingSource :- The widespread regulation of microRNAbiogenesis, function and decay by Jacek Krol, IngaLoedige and Witold Filipowicz.
Future perspectives• The past several years have witnessed tremendous progress in our understanding of miRNAs.• Still several important questions remain to be answered.• Understanding how miRNAs are processed and how they are integrated into the complex regulatory networks will be crucial.• Considering the fundamental role of miRNAs in organismal development, cellular differentiation and metabolism, viral infection, and oncogenesis, we can anticipate many more sophisticated mechanisms for the regulation of their biogenesis, function and catabolism to emerge in coming years.
References• The widespread regulation of microRNA biogenesis, function and decay by Jacek Krol, Inga Loedige and Witold Filipowicz.• MicroRNA Functions by Natascha Bushati and Stephen M. Cohen.• MicroRNA-9a ensures the precise specification of sensory organ precursors in Drosophila by Yan Li, Fay Wang, Jin-A Lee, et al.• Oncomirs — microRNAs with a role in cancer by Aurora Esquela- Kerscher and Frank J. Slack