Gene Silencing By Methylation Rather Than By Gene Mutation

GENE SILENCING BY METHYLATION RATHER THAN BY GENE MUTATION

Chapter one

Introduction

1.1  Background of the study

Gene silencing is the regulation of gene expression in a cell to prevent the expression of a certain gene. Dao, D., et al. 1999, Christofori, G., Naik, P., and Hanahan, D. 1995 Gene silencing can occur during either transcription or translation and is often used in research. Okano, M., Bell, D.W., Haber, D.A., and Li, E. 1999, Robertson, K.D., et al. 1999 In particular, methods used to silence genes are being increasingly used to produce therapeutics to combat cancer and other diseases, such as infectious diseases and neurodegenerative disorders.

Gene silencing is often considered the same as gene knockdown. Ohtani-Fujita, N., et al. 1997, Herman, J.G., et al. 1994 when genes are silenced, their expression is reduced. Li, E., Bestor, T.H., and Jaenisch, R. 1992 Nan, X., et al. 1998 In contrast, when genes are knocked out, they are completely erased from the organism’s genome and, thus, have no expression. Hoshikawa, Y., Kwon, H.J., Yoshida, M., Horinouchi, S., and Beppu, T. 1994 Cameron, E.E., Bachman, K.E., Myohanen, S., Herman, J.G., and Baylin, S.B. 1999 Gene silencing is considered a gene knockdown mechanism since the methods used to silence genes, such as RNAi, CRISPR, or siRNA, generally reduce the expression of a gene by at least 70% but do not completely eliminate it. Methods using gene silencing are often considered better than gene knockouts since they allow researchers to study essential genes that are required for the animal models to survive and cannot be removed. In addition, they provide a more complete view on the development of diseases since diseases are generally associated with genes that have a reduced expression. Prowse, A.H., et al. 1997

1.2 Statement of the Problem

RNA interference (RNAi) was demonstrated in a landmark article that revealed potent sequence specific gene silencing via double-stranded RNA injection in C. elegans (Fire et al., 1998). These ground-breaking experiments revealed that double-stranded sequences corresponding to exonic sequences produced silencing of complementary mRNA transcripts, whereas intronic and promoter sequences had no effect. Specifically, sense or antisense RNA individually had modest to little effect on the target gene compared to mutant phenotypes observed with double-stranded RNA (dsRNA). A similar twitching phenotype in progeny of injected animals was produced following injection of unc-22 dsRNA when compared to animals with loss-of-function mutations, consistent with disruption of myofilament protein motile function. This novel silencing mechanism was capable of crossing cellular boundaries and traversing into the germline. Additionally, the robust silencing and targeting of genes distant from the site of injection suggested the involvement of a catalytic component and/or RNA-transport mechanism. This essential discovery ushered in an era of reverse genetic studies aimed at deciphering the RNAi pathway and elucidating key mediators of this process. The rest of this introduction will highlight major milestones in elucidating the RNAi pathway and focus on two important mediators of RNAi—microRNAs (miRNAs) and small interfering RNAs (siRNAS). The history of these small ~23-25 nucleotide (nt) noncoding RNA molecules and their roles in gene regulation including post-transcriptional gene silencing 2 (PTGS – referring to RNA suppression) and transcriptional gene silencing (TGS – referring to DNA suppression) will be expanded upon.

1.3 Objective of the Study

1. To examine the regulation of gene expressionin a cell
2. To examine the process of preventing the expression of a certain gene
3. To examine the challenges of gene silencing in humans

1.4 Research Questions

1. What is the effect of regulation of gene expressionin a cell?
2. What is the process of preventing the expression of a certain gene?
3. What are the challenges of gene silencing in humans?

1.5 Hypotheses

1. There is no significant effect of regulation of gene expressionin a cell.
2. There is no significant effect of the process of preventing the expression of a certain gene.
3. There is no significant effect of the challenges of gene silencing in humans.

1.6 Significance of the study

The findings of this study will be useful in many ways. It shall be of great importance to the key players in the health care sector of the Nigerian economy. Moreover, the study will offer the needed information for the ministry of health, the World Health Organization (WHO), UNICEF, National centre for Disease control (NCDC)

Additionally, this study will form the basis for further academic research work for other researchers in the related topic of study and will also add to the existing stock of knowledge in the area of study.

1.8 Delimitation of the Study

The literature review carried out for this project is based on secondary data from unpublished literature, published journals and reports mostly by foreigner, therefore, any error observed in the primary data may have affected the reliability of the work.

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