DNA microarrays

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DNA microarrays[1]. are used in functional genomics to determine the differences in gene expression levels between a sample and control cell[2]. The sample cell can be: from a different tissue, at a different stage of development, at a different stage of the cell cycle, or be under different conditions (for example, exposure to a toxin)[2]. In the DNA microarrays, there are closely packed gene-specific sequences are exist and they are bound to the surface of a glass microscope slide[3]. The DNA microarray consists of a flat surface to which oligonucleotides are bound[2]. These oligonucleotides are complementary to specific cDNA sequences[2]. Additionally, the oligonucleotides generally around 20 nucleotides lenght and they are synthesised from the previously attached gene-specific sequences to the glass microscope slide[4]. . The mRNA molecules within the sample and the control are converted into labelled cDNA molecules with the use of reverse transcriptase and fluorescently-labelled nucleotides[2].

For example, the cDNA of the sample can have a red fluorescence label whereas the cDNA of the control can have a green fluorescence label[2]. The DNA microarray is exposed to the cDNA mixture and unbound cDNA is washed away[2]. The resultant DNA microarray consists of spots of colour that is imaged using a confocal fluorescence scanner[2]. The colour of the spot is indicative of the differences in gene expression between the sample and control[2]. Following the colour scheme above, a red spot indicates that the sample is overexpressing that particular gene compared to the control; a green spot indicates that the sample is underexpressing that particular gene compared to the control; and a yellow spot indicates that there is equal gene expression in the sample and control[2]. However, the range of colours is not as discrete as suggested here, it is more of a spectrum covering intermediate differences in gene expression[2]. DNA microarrays are not so useful in determining gene function but can ascertain which genes may have the same regulatory mechanisms[2].

An Application of Microarray Experiment

An experiment by Lagogue et al. in 2006 showed that resveratrol (an anti-ageing component, contained in the skin of red grapes) is able to shift the high-calorie driven pathway in the mice[5].

The mRNA sample from mice with high-calorie diet and from mice with high resveratrol diet were taken. Both were then tested by DNA Microarray to monitor and to compare the level of gene expressions. After analysing using DNA Microarray, it was found that resveratrol was able to reverse the effect of high-calorie diet on 144 out of 153 significantly altered pathways in mice.

The DNA Microarray technology enables the researchers to monitor the level of gene expressions quickly and more efficiently.

References

  1. http://learn.genetics.utah.edu/content/labs/microarray/
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 Daniel L. Hartl, Elizabeth W. Jones (2009) Genetics Analysis of Genes and Genomes 7th Edition USA, Jones and Bartlett Publishers.
  3. Lodish H., Berk A., Kaiser C A., Krieger M., Bretscher A., Ploegh H., Amon A., Scott M P. (2013) Molecular Cell Biology, 7th Edition, New York: W.H. Freeman and Company
  4. Lodish H., Berk A., Kaiser C A., Krieger M., Bretscher A., Ploegh H., Amon A., Scott M P. (2013) Molecular Cell Biology, 7th Edition, New York: W.H. Freeman and Company
  5. Lagouge et al (2006) "Resveratrol improves mitochondrial function and protects against metabolic disease by activating Sirt1 and PGC-1alpha". Cell 127: 1109-1122
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