Question

Describe DNA microarray analysis to identify which genes are expressed at a particular developmental stage and in a particular cell type. What type of molecules should be attached to the microarray? What should be fluorescently labeled and be part of the hybridization solution? How can one determine when analyzing the results of such an experiment?

Answer 1

The microarrays are also known as gene chips. The single stranded DNA molecules are spotted on to a glass slide through a computer controlled high speed robotic arm called an arrayer. An arrayer contains several tiny pins and each pin is immersed in a solution containing million copies of single stranded DNA molecules. The complementary DNA for the single stranded DNA molecules on the microarray are expressed as sequence tags. An arrayer spots the DNA on the slide at specific location that is recorded by the computer.

A single microarray can have about 20000 separate spots of DNA with a unique sequence specified for each gene. The entire genome can be available on microarrays including a human genome. The microarrays are used for the comparison of the pattern of gene expression in normal tissues to that of gene expression in diseased tissues to identify the pathogen. Computerized microarray data provides the analysis of increased or decreased gene expression under experimental condition. Microarrays enable the study of thousands of genes at a time and can generate huge amount of gene expression data.

The microarray technology is involved in the comparison of gene expression in different cells or tissue samples. The cDNA prepared from a tissue is labeled with one color of dye and the cDNA from other tissue is labeled with another colored dye. The labeled cDNAs are subjected to denaturation and incubated overnight with the microarray. This will lead to hybridization of labeled cDNA with the spots on the microarray containing the complementary DNA sequences. The microarray is then washed and scanned by laser to get the florescence from the hybridized spots. The patterns of the florescent spots give the idea about the genes that are expressed in the tissue under examination. The better florescence gives the relative level of expression of the gene.