MicroRNA and thier role in gene regulation

MicroRNA and thier role in gene regulation

1. microRNA and their role in gene regulation

2. Introduction; Definition ; “ micro RNA is a small non-coding RNA molecule that function in RNA silencing and post transcriptional regulation of gene expression.”

3. History; First miRNA was discovered in 1993 by a group led by Ambros . Its mode of action publication was published by Ruvkun’s team. In 2000 and 2 nd small RNA was characterize. The first human diseases associated with deregulation of miRNA was chronic lymphocytic leukemia.

4. Location : On the basis of organism; plants. animal. some virus. On the basis of cell; Majority miRNA within the cell. Some are extracellular.

5. Terminology : DGCR 8 : ( DeGeoge syndrome Critical Region): “ microproceser complex sub unit is a protein that in human encoded by the DGCR 8 gene, but in other organism like Drosophilla melanogester such protein is called Pasha . Drosha : is a class 2 ribonuclease 111 enzyme that in human encoded by the drosha gene.

6. Conti… Exportin 5 : transporter protein that transport precurser miRNA from nucluce to cytoplasm. Dicer : dicer is also known as endoribonuclease Diser or helicase , is enzyme that in human is encoded by Dicer gene. Dicer cleave double stand miRNA and pre- miRNa in to short double stranded RNA.

7. Conti.. AGO2 protein : ( stand for Argonaute ) this protein family play a central role in RNA silencing process, as essential component of the Risc (RNA inducer silencing complex ). RISC : is a multi protein complex which incorporate one stand of a single stranded RNA( ssRNA ) fragment, such as miRNA . The single strand act as a templet for RISK to recognize complementary mRNA transcript and through Argonute , it cleave the mRNA and this phenomena is called RNA interference.

8. Biogenesis and function : Biogenesis of mircoRNA : this process is carry out in two places of the cell; Nucleus: Transcription Nuclear processing Nuclear export. Cytoplasm:

9. Nucleus: Transcription : miRNA usually transcribe by polymerase 11 enzyme. Poly 11 attached with the promoter region of the DNA sequence and transcribe the DNA. The resulting transcript is capped with specially modified nucleotide at the 5’ end and spliced.

10. Nuclear processing: Formation of hairpin loop structure. Hairpin is composed of 70 NT each. This hairpin is recognized through type of protein called GDCR 8. GDCR 8 associated with Drosha that cut DNA making micro processing complex. This complex convert the pri -miRNA to pre-miRNA. Pre-miRNA that are spliced is known as " Mirtrons ”.

11. Nuclear export: Pre-miRNA transport through a nucleocytoplasmic transporter protein known as Exportin-5 . Use GTP as energy.

12. Cytoplasmic processing: the pre-miRNA hairpin is cleaved by the RNase III enzyme Dicer . Dicer interact with the 5’ and 3’ hairpin and cut the loop.(means shorting the dsmiRNA ). AGO2 bind with the dsmiRNA and unwinded and convert to single stranded guide miRNA. Guide strand is complementary to the target mRNA and inactivate the mRNA trough two process. Cut on mRNA . Inhibition.

13. RNA induce silencing complex(RISC). Also known as microRNA ribonucleoprotein complex. Mature miRNA incorporate with RISC, which contain Dicer and many other associated proteins. Argonaute protein(endonuclease) in RISC induce silencing, which contain two domains one for binding miRNA at 3’ end and other for binding with 5’ end of miRNA. Argonautes cleave target transcripts directly and sometime recruit additional proteins to achieve translational repression. And this depend on the complementarity of miRNA with mRNA.

14. Mode of silencing. Silencing may occur either through degradation or preventing mRNA from being translated. The relation of miRNA and its target is base on negative regulation of target mRNA. Here common scenario is use i -e feed-forward loop.

15. Cellular Functions of miRNA MicroRNA role in translation process. Repression mechanism on the initiation complex or recruiting 40S ribosomal subunit(M1). Repression mechanism on ribosome assembly(M2). Repression mechanism on translation process(M3). Degradation of mRNA(M7,M8)

16. Nine Mechanism Of miRNA In Gene Regulation. 40S initiation inhibition. 60S ribosomal unit joining inhibition. Elongation inhibition. Ribosome drop-off(premature termination). Co-translational nascent protein degradation. Sequestration in P-bodies.

17. Continue……… mRNA decaying(destabilization) mRNA cleavage. Transcriptional inhibition through miRNA-mediated chromatin reorganization followed by gene silencing.