Gene silencing

Gene silencing is the regulation of gene expression in a cell to prevent the expression of a certain gene. Gene silencing can occur during either transcription or translation and is often used in research.

1. GENE SILENCING Register no-189422 Guide- Dr Sohail Keegan Pinto

2. CONTENTS

3. INTRODUCTION Gene silencing is the regulation of gene expression in a cell which prevents the expression of certain gene. It describes the switching off of a gene by a mechanism other than genetic modification. It occurs when the RNA is unable to produce a protein during translation. Gene silencing is a “knock down” process. When genes are knocked down , their expression is reduced. In contrast, when genes are knocked out ,they are completely erased from organism's genome and has no expression.

4. http://www.newbornscreening.info/Pro/genetics.html

5. http://www.newbornscreening.info/Pro/genetics.html

6. DIFFERENT APPROACHES OF GENE SILENCING Gene knock out Gene knock down Gene silencing and degradation of gene using RNA technology -Antisense RNA technology -RNA interference(RNAi) technology There are mainly two types of gene silencing 1)Transriptional gene silencing 2)Post transcriptional gene silencing

7. Gene silencing can be induced either at transcriptional level or post transriptional level. Transcriptional level Post transcriptional level Genomic imprinting Anti sense RNA technology Position effect RNA interference -mi RNA -sh RNA -si RNA

8. TRANSCRIPTIONAL GENE SILENCING It is acheived by creating of environment of heterochromatin around a gene that makes it inaccesible to transcriptional machinery (RNA polymerase,transcription factors etc.) 1)Genomic imprinting Genomic imprinting occurs when a gene inherited from either mother or father has been permanently inactivated in the parent and passed on to offsprings in the same inactivated condition. 2)Position effect Position effect is the effect on the expression of a gene when its location on a chromosome is changed, often by translocation.

9. POST TRANSCRIPTIONAL GENE SILENCING It is the ability of endogenous or exogenous RNA to supress the expression of the gene that corresponds to m-RNA sequence. 1) Antisense RNA technology Antisense RNA is a single stranded RNA that is complementary to a mRNA strand.They are introduced into a cell to inhibit the translational machinery by base pairing with the sense RNA and activating the RNase H.

10. Antisense RNA technology https://www.ukessays.com/essays/sciences/antisense-technology-applications-7151.php

11. 2)RNA interference( RNA i) It is a cellular process by which mRNA is targeted for degredation by a dsRNA with a strand complementary to a fragment of mRNA. During RNA i, dsRNA cut into small dsRNAs by an enzyme called dicer. They base pair to an mRNA through a double stranded RNA-enzyme complex (RISC). There are 3 types of dsRNA produced that leads to RNAi pathway; 1)Small interfering RNAs (si RNAs) 2)micro RNAs (mi RNAs) 3)Short hairpin RNAs (sh RNA)

12. There are five components for siRNA ,miRNA and shRNA generation Drosha Dicer RNA-induced silencing complex (Risc) Argonaute RNA dependent RNA polymerase

13. siRNA pathway Produced in vivo by by cleavage of dsRNA. Complementary to aspecific sequence of target mRNA for degradation. 3 phases: Initiation phase Maintenance phase Signal amplification and spreading phase

14. siRNA mediated RNAi pathway https://www.nature.com/articles/nrg3978 dsRNA are chopped into short interfering RNAs(si RNA) by dicer. The siRNA and dicer complex recruits additional component to form an RISC . The siRNA unwinds. The unwound siRNAbase pairs with complementary mRNA, thus guiding the RNAi machinery to the target mRNA. The target mRNA is effectively cleaved and subsequently degraded.

15. miRNA pathway It is a single stranded RNA molecule, 22-25 nucleotides Primary transcript is processed to a short structure called a pre- miRNA and finally into a funtional miRNA. 2 phases: Initiation -Generation of mature miRNA Execution -Silencing of target gene -Degradation or inhibition of translation.

16. miRNA mediated RNAi pathway https://www.ous-research.no/kristensen/?k=kristensen%2FResearch+projects&aid=12836

17. shRNA pathway https://www.researchgate.net/figure/Three-strategies-to-enhance-si-or-shRNA-efficiencies-in-mammalian-cells-schemes-A_fig1_256764704 There are 5 components for siRNAs generation 1)Dicer 2)Short hairpin RNA 3) RISC 4)Argonuate 5) Rna dependent RNA polymerase

18. Applications of gene silencing Specific gene silencing using RNA i in cell culture Cancer treatment RNAi has been used in biotechnology, particularly in the engineering of food plants that produce lower levels of natural plant toxins. Modulation of HIV -1 replication by RNA i.

19. References Molecular biology by David p. Clark ELSEVIER. Elbashir S.M. et al., 2001. RNA interference is mediated by 21- and 22-nucleotide RNAs. Genes Dev, 15(2):188-200. Nelson, D., Nelson, D., Lehninger, A. and Cox, M. (2008). Lehninger principles of biochemistry. 5th ed. New York: W.H. Freeman, pp-.1110-1113.