Regulation of Gene Expression - Case Study Example

Regulation of gene expression Introduction: Gene expression refers to the manifestation of a phenotypic character by the activity of the gene. A gene expresses its character by producing proteins or enzymes. During gene expression, there is flow of genetic information from DNA to proteins. Gene expression involves two main steps, namely transcription and translation. Regulation of gene expression: Each adult cell contains the full set of genes necessary for the development of an adult animal. However in any cell all the genes will not function to synthesize proteins. Only one or few genes will be functioning in any adult. The other genes will not function and synthesize proteins. The genes which are functioning are called switched on and not functioning is called as switched off. In the Islets of Langerhans, the genes responsible for the synthesis of insulin are switched on and all other genes are switched off; in the cells of oviduct, the genes responsible for ovalbumin are switched on and all other genes are switched off. Regulation of Gene Expression in Prokaryotes: In Prokaryotes, the gene expression is regulated at two levels, as regulation of enzyme and regulation of transcription. Regulation of Gene Expression in Eukaryotes: In Eukaryotes, when all the genes are functioning at the time, the cell will be flooded with enzymes and proteins. At any one time, the required enzymes are produced. Other enzymes which are not required are not synthesized. The genes for the required enzymes are switched on and the other genes are switched off. This on and off mechanism was explained by the operon model. In eukaryotes, the regulation of the regulation of gene expression is brought about at three levels, namely transcription, processing and translation. Phenotype is nothing but the expression level of the organisms genes and the environmental l factors. The genotype is the instruction carried out by the genes. These genes are present in the chromosome. The chromosome responsible for insulin synthesis and regulation are present in the chromosome 20. The SNPs present in the chromosome 20, (rs12255372 and rs7903146 ) are responsible for the function of the protein. Diabetes Mellitus is a group of metabolic diseases that occurs in a person if they have high blood sugar or less production of insulin or the cells may not respond well to the insulin that is produced. There are three main types of diabetes. (Krentz and Bailey 2005). 1. Type 1 Diabetes – This is characterized by the loss of producing ability of the beta cells by the islets of langerhans. This type will affect the children and the adults. It is called as “juvenile diabetes" because it occurs in most of the children. This is one of the life threatening diseases. This disease has a greater prevalence of premature complications and mortality than the other forms of disease. (Barroso 2005). 2. Type 2 Diabetes: In this type, insulin is produced in the body but the cells don’t have the ability to use them. This type is mainly associated with obesity, gestational diabetes, family history of diabetes, impaired glucose metabolism, race, ethnicity etc., this type affects the adults who had signs of diabetes at their earlier stage. 3. Gestational Diabetes: The carbohydrate intolerance usually develops at the 24th through the 32nd week of pregnancy in some people. This condition is present in almost 2-5 % of all the pregnant women. This type can be easily controlled by diet. There is a chance of about 40-60 % of these pregnant ladies to develop diabetes at the later stage. This elevated level of glucose will increase the complications between the mother and the child. Type II diabetes mellitus is a non insulin dependent diabetic disorder. This is found as one of the leading factors and is found to occur due to changes in the genes. This is identified by the high blood glucose content and less insulin presence in the body. Diabetes is usually reduced or modified by diet and exercise. But some people are not exposed to any type of diabetes. They are found in some parts of Saudi Arabia. Type 2 diabetes is mainly caused by the life style factors and also because of genetics. But some group of people in Saudi Arabia are enjoying the same life style but are not exposed to diabetes. Some of the reasons may be the insulin resistance gene. Some of the international research teams after a wide research have found that a gene present in the chromosome 20 was responsible for the occurrence of diabetes mellitus II in the human. (Zhang et al. 2006). The team has also identified that four single nucleotide polymorphisms present in the chromosome 20 are the four genetic variants. These SNPs are found as a cluster in the regulatory region of the gene hepatocyte nuclear factor 4 alpha. (HNF4A). This HNF4A is one of the most important factors in the transcription and it regulates hundreds of genes and their expression levels are controlled by this gene. They act as master switches for many regulations. These Master switches turns on the genes in the liver and the pancreas. They also turn on the beta cells of the islets of Langerhans. These beta cells are much responsible for the production of insulin. Along with these 4 SNPs , there are 6 more found near it are found to be associated with the type 2 diabetes.(Saxena et al. 2006). The over eating of the people induces short term resistance to insulin. The insulin resistance is relsted to the T2D. This was confirmed from the insulin signaling process in the adipocytes. The scientists have found that HNF4A is the most important highly active transcription factor that is found to regulate the beta cells. They are also found in the liver cells of the humans. They have also found that a ‘mislead’, in the binding site of the transcription factor will result in the mis-regulation of the beta cells. This may finally lead to the malfunction and diabetes. (McCarthy, 2004). In order to study about the logistic regression present between the four types of SNPs, non parametric multifactor dimensionality reduction and the modified and generalized MDR are used. They were used to confirm the findings that are present. The rate of interaction between the SNPs was found using the parametric and non parametric methods. The Four genes are TCF7L2, HNF4A, KCNJ11, and WFS1. These genes are found to play an important role and association with the type 2 Diabetes (T2D). The mechanical and biological effects of T2D were studied by a group of scientists. It was found that when using the single nucleotide polymorphism for genotyping, the SNPs were found to be associated with the T2D and also found that the gene TCF7L2 was the only universal gene found associated with the T2D. Many studies have also proved that two intronic SNPs rs12255372 and rs7903146 are found to be associated with the T2D. Along with that the gene HNF4A SNP and the intronic SNP rs1884613 are also having a strong relationship between each other. Rs1884613 is present in the upstream of the gene HNF4A. This particular SNP does not have any specific function. Along with the HNF4A, the potassium channel gene KCNJ11 is found on the chromosome 11p15.1 regulates glucose-induced insulin secretion in the pancreatic cells. Similarly the gene WFS1 gene was recently found to be involved with the T2D. (Alsmadi et al, 2008). The genotypic frequencies were different between the T2D and the normal people. If all the alleles are present in the same chromosome and interact well, the prevalence of T2D will be high. (Neuman et al. 2010). In the Saudi Arabian population, among the 27 studies performed, it was found that rs7903146 and rs12255372 variants of TCF7L2, which are the most important variants for the occurrence of T2D were not present in some groups of the Saudi Arabia. The scientists have also reported that there is a marginal association between the rs12255372 variants of TCF7L2 with the type 2 diabetes mellitus and no association between rs7903146 and T2D. (Rosalind et al. 2010). In the study performed by Alsmadi et al., the participants were selected randomly with no relationship among them. They were selected based on the WHO criteria. The total number of participants selected was 522. The peripheral blood samples were collected from them and stored in the EDTA anticoagulant tubes. The DNA was isolated from these samples and was quantified. The PCR was then performed using the thermal cycler for 35 cycles at heated lead conditions. The primers for this experiment were designed using the PSQ assay design software. After PCR amplification, pyro sequencing was performed to determine the sequence and the allele location in the DNA. These DNA samples were then biotinylated and immobilized into the beads. They were then used for the screening purpose. The single stranded DNA sequencing template were then isolated using the immobilized beads. These primed DNA were then isolated and kept in the pyrosequencing machine. Using the pyrosequencing machine, the 96 well titer plate was filled with the genotypes. The SNP which act as replicates were added to the plates and analyzed. These plates were genotyped with 100% concordance. The rate of these SNP genotyping ranged between 93-98 % for the successive runs. Conclusion: It was found clearly that there is a strong association between the rs12255372 variants of TCF7L2 with the type 2 diabetes mellitus. The lack of these genes or the off condition of these genes may be the reason for the non incidence of diabetes mellitus type2 in the southern region of the Saudi Arabia. References: Alsmadi, O et al 2008, Genetic study of Saudi diabetes (GSSD): significant association of the KCNJ11 E23K polymorphism with type 2 diabetes, Diabetes/Metabolism Research and Reviews, vol. 24, no. 2, pp.137-40. Krentz, AJ and Bailey, CJ 2005, Type 2 Diabetes in practice, 2nd Edition, RSM Press. Barroso, I 2005, Genetics of Type 2 diabetes, Diabetic Medicine, vol. 22, no. 5, pp. 517–535. McCarthy, MI 2004, Progress in defining the molecular basis of type 2 diabetes mellitus through susceptibility-gene identification, Human Molecular Genetics, vol. 13, pp. 33–41. Neuman, RJ et al. 2010, Gene-Gene Interactions Lead to Higher Risk for Development of Type 2 Diabetes in an Ashkenazi Jewish Population, PLoS One, vol. 5, no. 3. Saxena, R et al 2006, Common single nucleotide polymorphisms in TCF7L2 are reproducibly associated with type 2 diabetes and reduce the insulin response to glucose in nondiabetic individuals, Diabetes, vol. 55, pp. 2890–2895. Zhang, C et al 2006, Variant of transcription factor 7-like 2 (TCF7L2) gene and the risk of type 2 diabetes in large cohorts of U.S. women and men, Diabetes, vol. 55, pp. 2645–2668. Read More