Microarrays a relatively
new Analytical technique
By
Dr. Shahila Mehboob
Assistant Professor, University of Illinois at Chicago
Microarrays
Microarrays is an analytical
technique of recent origin (about ten years old). It is used in the
study of the pattern of gene expression of thousands of genes at the
same time. Genes are regions of the genome that code for a specific
protein. Different genes are expressed at different stages of growth
and can also be expressed in response to diferent environmental conditions.
Biologists are often interested in understanding which genes are expressed
under which conditions; for instance, under aerobic, anaerobic conditions,
in the presence of an antibiotic for those bacteria that are resistant
and so on. This would help in understanding diseases at a molecular
level thereby aid in developing better drugs.
The microarray technique
involves spotting tens of thousands of DNA/RNA molecules on a slide
with each spot uniquely identifying a unique region of the genome. These
molecules can be small (~25 bps) or even somewhat larger. In some experiments
molecules upto 500 bps have been used. This spotting on a slide is generally
done commercially by well established companies, Affimetrix is one of
them, refer to their website at:
http://www.affimetrix.com/corporate/media/genechip_essentials/gene_expression/How_the_Array_Works.affx
In order to figure out which
genes are expressed under a given set of conditions, cells in that conditions
are taken along with cells in the control conditions. mRNA from these
cells are extracted (mRNA represents the genes that are turned on in
these cells) and then labelled. The labels normaly incorporated are
green and red, the labelling technique differs based on the method used.
One of the methods is to use a labelled poly T tail as a primer and
synthesize the cDNA using PCR. The labelled cDNA from both samples(
the sample and control) are mixed together and washed on the micro array
slide, when hybridization occurs. Each spot on the slide is now one
of four colours: green, red, yellow or black. The colors correspond
to the expression of the gene under different conditions. Spots that
are only green are highly expressed in the control while spots that
are red are highly expressed in the sample. Spots that are yellow are
equally expressed in both sample and control and black spots are genes
that are not expressed in either sample are control.
An animated version of this
techniqe can be seen in the website :
http://www.bio.davidson.edu/courses/genomics/chip/chip.html
http:/www.imagecyte.com/array2.html
For more information and guidance contact the author
through: mpeeran@gmail.com |