PCR Changes the World of Molecular Biology
PCR
Changes the World of Molecular Biology
Since its discovery, PCR
has
established itself as the most reliable technique that is accelerating
biotech research and gaining prominence in almost all areas of life
sciences.
The discovery of polymerase chain reaction or PCR has forever changed
the molecular biology world. It is an indispensable research technique
capable of producing billions of copies of a DNA fragment from just few
copies, in less than two hours and is used for a variety of medical and
biological applications from basic gene sequencing, diagnosis of
hereditary diseases, the identification of genetic fingerprints, the
detection and diagnosis of infectious diseases to the creation of
transgenic organisms.
Following its invention 26 years ago, PCR has been adapted extensively
for numerous molecular biology applications. Gene expression analysis
by reverse-transcription quantitative PCR (RT-qPCR) has been a key
enabling technology of the post-genome era. PCR is also the lone
technique that helped the synthetic oligonucleotide business become a
thriving industry today.
PCR suppliers in India
Players with
direct presence
Players with
indirect presence
- ABI (Through Labindia)
- Bioneer (Krypton Biomedicals)
- Cepheid (Through Biotron Healthcare)
- Stratagene (Through Genetix)
- Takara (DSS Imagetech)
- Techne (Scientech, Carebio medicals)
|
The invention
Kary Mullis, who earned a PhD in biochemistry from University of
California, Berkeley in 1973, conceived PCR as a means to amplify a
specific locus of interest on the human genome in 1983 .
After conceptualizing PCR, Kary labored for a number of months to work
out experimental conditions. Since thermostable polymerases were not
yet available, it was necessary to add Klenow after each thermal cycle,
adding to the tedium of development. There were many failures and many
reasons why PCR should not work. Ignoring the doubts of many,
the
scientist was able to perform his first successful experiment on
December 16, 1983. A patent for PCR was awarded to Cetus Corporation,
where Mullis worked when he invented the technique in 1983. The Taq
polymerase enzyme was also covered by patents. Perkin-Elmer partnered
with Cetus to commercially introduce a thermal cycler in the market.
This platform was based on compressor driven refrigeration
technology. Few years later, pharmaceutical major Hoffman La
Roche purchased the rights to the patents in 1992 and currently holds
those that are still protected.
Evolution of
technology
As PCR introduced capabilities to identify, manipulate, and amplify
DNA, research possibilities flourished. The detection of genetic
mutations, the ability to detect the presence of previously unknown
genetic material, as well as the ability to analyze degraded DNA, all
became common practice. For example, diseases such as muscular
dystrophy and HIV could be detected and diagnosed with the use of PCR.
As scientists grew more familiar with the technique of PCR, they began
to expand on the utility of the method. And there have been a lot of
improvements in the technology, experimental design, and data analysis.
During the late 1980s PCR was used to measure the quantity of DNA
present in a reaction, generating the term “quantitative
PCR” or more simply, q-PCR. This technique further improved
PCR
by the isolation of Taq Polymerase in the early 1990s. qPCR and, more
specifically, real-time qPCR has become a routine and robust approach
for measuring the expression of genes of interest, validating
microarray experiments and monitoring biomarkers. The use of real-time
qPCR has nearly supplanted other approaches like Northern blotting and
RNase protection assays.
PCR technology and method has today reached a mature stage of
development and implementation. This technique further
improved
PCR by the isolation of Taq Polymerase in the early 1990s. The heat
stable polymerase could remain active through many cycles of heat
required for amplification and created the demand for faster cycling.
Russell Higuchi and associates developed a system to monitor the
amplification of DNA simultaneously to the reaction. The system
involved ethidium bromide, a thermal cycler to irradiate samples with
UV light, and a camera to record fluorescence.
“The introduction of Peltier-based temperature controlled
blocks
followed by the introduction of interchangeable blocks, multiple
blocks, low reaction volume blocks, blocks with high ramping rates, and
finally temperature gradient blocks led to global adoption of PCR. But,
the most radical innovation in this space was the development of
‘real-time’ platforms that measure the amount of
PCR
product made at the end of each cycle. Real-time PCR platforms and the
FRET- and SYBR Green-based chemistries enabling the same have become
cornerstones of modern genomics, especially for gene expression and
genetic analysis applications,” said Subramanian Dharmaraj,
senior marketing manager, genomics division, Labindia.
In the early 1990s, fluorogenic dual labeled probes were developed as a
means to practice q-PCR. In conjunction with fluorescent probes, PCR
had further evolved into a sensitive quantification tool useful for the
detection of any desired genetic element. As a result, the ability to
measure gene expression and practice genotyping quickly became trivial
and widespread throughout the biotechnology industry. Now, with the
recent development of new dyes and quenchers such as the series of
Black Hole Quencher, CAL Fluor and Quasar dyes, the possibilities for
PCR are seemingly endless.
Market
The real-time PCR market in itself has come a long way, since the
introduction of the first commercial real-time PCR platform by Applied
Biosystems. The focus has gradually changed from hardware to complete
end-to-end workflow-based solution. Gradually, other players also
started penetrating the market by introducing more user-friendly and
flexible products.
There are over 15 companies operating in this space globally. Applied
Biosystems has the highest share of the market with Bio-Rad,
Stratagene, Eppendorf and Roche being the other major stake holders in
the basic research market. Additionally, Corbett, Cepheid and Techne
are also trying to make inroads into this market. As further innovation
in instrument technology has been slowing down over the last few years,
one can expect that further growth in this market will be mainly driven
by innovative reagents and consumables for the next few years.
The use of molecular techniques in all segments of the clinical,
diagnostic and testing markets has been growing by leaps and bounds
over the last few years. This is the primary driver for the growth in
the PCR market at present. Major players in PCR market in India include
Applied Biosystems, Eppendorf, Bio-Rad, Stratagene, Techne, Corbett and
Cepheid.
Technology upgradations
During the developmental stage of this product line, real-time PCR was
perceived merely as an optical upgrade of conventional PCR. But as more
sophisticated applications were enabled by the real-time PCR technique,
instrument manufacturers also realized that the technique offered great
potential and the need for rapid improvements in their platforms. As a
result, hardware features including the light source, the detection
systems etc. were rapidly upgraded to keep pace with the application
development without diluting the cost to performance ratio. Innovative
approaches such as virtual filters were also implemented to deconvolute
complex fluorescent dye spectra thus achieving better signal to noise
ratios.
Even though, there are various real-time PCR chemistries available, two
chemistries are widely used by the scientists all over. These are
FRET-based TaqMan technology and SYBR Green chemistry which is
dependent on SYBR Green’s ability to bind any double-stranded
nucleic acid molecule. TaqMan chemistry is extremely accurate and
highly specific and considered to be the gold standard for real-time
PCR experiments. However, with proper optimization SYBR green based
methods can also work well.
Having sensed the need for speed and reliability, technology providers
have started offering ready-made off-the-shelf assays, customized
assays and optimized reagents enabling sample preparation from a wide
range of specimens. As of today, the entire focus has shifted to
provide complete work flow solutions to researchers. This has allowed
scientists to focus on the science and discovery rather than the
technique.
The most recent and novel innovation in this area has been the adoption
of the microarray format for running real-time PCR experiments. This
format allows researchers to interrogate the expression level of
hundreds of genes simultaneously. With increasing number of scientists
wanting a much closer view of gene expression at the pathway and
individual biological process level, which typically involves a few
hundred genes, these real-time PCR based low density arrays have
already become a very popular tool. These arrays are also becoming an
incredibly powerful tool to analyze global gene expression changes in
the entire miRNA gene set. The future of PCR remains bright as the
technology becomes more rapid, cost-effective, easier to use, and
capable of higher throughput.
Jahanara Parveen