Let us talk about microarrary: A
microarray is a laboratory tool used to detect the expression of thousands of
genes at the same time. The DNA molecules
attached to each slide act as probes to detect gene expression, which is also known as the transcriptome
or the set of messenger RNA
(mRNA) transcripts expressed by a group of genes. How to carry out such complicated difficult –to –understand
tests?? -Basic principle for clinicians: To perform a microarray analysis, mRNA
molecules are typically collected from both an experimental sample and a
reference sample. For example, the reference sample could be collected from a
healthy individual, and the experimental sample could be collected from an
individual with a disease like cancer. The two mRNA samples are then converted
into complementary DNA (cDNA), and
each sample is labeled with a fluorescent probe of a different color.
For instance, the experimental cDNA
sample may be labeled with a red fluorescent dye, whereas the reference cDNA may be labeled with a
green fluorescent dye.
What are gene chips??? DNA microarrays are microscope slides that
are printed with thousands of tiny spots in defined positions, with each spot
containing a known DNA sequence or gene. Often, these slides are referred to as
gene chips or DNA chips. The DNA molecules attached to each slide act as probes
to detect gene expression, which is also known as the transcriptome or the set
of messenger RNA (mRNA) transcripts expressed by a group of genes.
What is DNA Microarray?? Ans:-DNA
Microarray is a kind of “Molecular Biology research”. Microarray is one such technology which enables the
researchers to investigate and address issues which were once thought to be non
traceable. One can analyze the expression of many genes in a single reaction
quickly and in an efficient manner
What do we mean by DNA probes?? Ans:-
Thousands of spotted samples known as probes (with known identity) are
immobilized on a solid support (a microscope glass slides or silicon chips or
nylon membrane). The spots can be DNA, cDNA, or oligonucleotides. These are
used to determine complementary binding of the unknown sequences thus allowing
parallel analysis for gene expression and gene discovery. An experiment with a
single DNA chip can provide information on thousands of genes simultaneously.
An orderly arrangement of the probes on the support is important as the
location of each spot on the array is used for the identification of a gene
The principle of microarray?? Ans;
A typical microarray experiment involves the hybridization of an mRNA molecule
to the DNA template from which it is originated. Many DNA samples are used to
construct an array. The amount of mRNA bound to each site on the array
indicates the expression level of the various genes. This number may run in
thousands. All the data is collected and a profile is generated for gene
expression in the cell.
What is hybridization??? Ans:-The two samples are then mixed together and allowed to
bind to the microarray slide. The process in which the cDNA molecules bind to
the DNA probes on the slide is called
hybridization. Following hybridization, the microarray is scanned to
measure the expression of each gene printed on the slide. If the expression of a particular gene is higher in the experimental
sample than in the reference sample, then the corresponding spot on the
microarray appears red. But if the, if the expression in the experimental sample is lower than in the reference sample, then
the spot appears green. Finally, if there is equal expression in the two
samples, then the spot appears yellow. The data gathered through
microarrays can be used to create gene expression profiles, which show
simultaneous changes in the expression of many genes in response to a
particular condition or treatment.
ABC of Microarray technology &
We the clinicians!!! :- It
essentially compare the differences if any, between RNA
prepared from suspected diseased cells
and RNA prepared from normal
cells . I hope this will suffice. If one is thirsty to know details, well I
am afraid she/ he will forget details of microarray technology even I describe some basic aspects of microarray.
Microarray technology is a powerful technique used
to compare differences in gene expression between two mRNA samples. Comparing RNA prepared from diseased
cells and RNA prepared from
normal cells one will be able to identify
a set of genes that play key roles in some diseases.
Kinds of microarray
testing –simplifying for the clinicians:-Microarray experiments can for the clinicians
can be categorized in three ways:A) Microarray Expression Analysis
B) Microarray for Mutation
Analysis C) Comparative Genomic Hybridization. Let us view all such
procedures.
1. Microarray Expression Analysis: In
this experimental setup, the cDNA derived from the mRNA of known genes is
immobilized. The sample has genes from both the normal as well as the diseased
tissues. Spots with more intensity are obtained for diseased tissue gene if the
gene is over expressed in the diseased condition. This expression pattern is
then compared to the expression pattern of a gene responsible for a disease.
2. Microarray for Mutation Analysis: For this analysis,
the researchers use gDNA. The genes might differ from each other by as less as
a single nucleotide base.
A single base difference between two sequences is known
as Single Nucleotide Polymorphism (SNP) and detecting them is known as SNP
detection.
3. Comparative Genomic Hybridization: It
is used for the identification in the increase or decrease of the important
chromosomal fragments harboring genes involved in a disease.
Applications of Microarrays
Gene Discovery: DNA
Microarray technology helps in the identification of new genes, know about
their functioning and expression levels under different conditions.
Disease Diagnosis: DNA Microarray technology helps researchers learn more
about different diseases such as heart diseases, mental illness, infectious
disease and especially the study of cancer. Until recently, different types of
cancer have been classified on the basis of the organs in which the tumors
develop. Now, with the evolution of microarray technology, it will be possible
for the researchers to further classify the types of cancer on the basis of the
patterns of gene activity in the tumor cells. This will tremendously help the
pharmaceutical community to develop more effective drugs as the treatment
strategies will be targeted directly to the specific type of cancer
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