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Article on gene expression
I received this through another e-mail service and
thought it was interesting. While it does not
directly discuss radiation, I think that the finding
will have implications for the study of radiation
effects. Specifically, all genes are not equally
mutated by radiation. Rather, active genes are at
higher risk of mutation. Thus, all segments of the
DNA do NOT have the same risk factor for mutation.
The reference to the scientific article is:
H.R. Ueda et al., .Universality and flexibility in
gene expression from bacteria to human,. PNAS,
DOI:10.1073/pnas.0306244101, March 1, 2004.
http://www.pnas.org/
The following article is at
http://www.biomedcentral.com/news/20040303/01
------------------------
Power law governs gene expression
Proportional dynamics illustrates commonality of gene
expression levels in all organisms
| By Cathy Holding
With an ever-increasing number of genomes available
for analysis, there has been a shift in emphasis away
from the study of single genes and a greater attempt
to understand gene expression at the network or
systems level. A report in the March 1 PNAS shows that
power laws.a universal mathematical dynamic.govern the
process.
Hiroki Ueda and colleagues at the Center for
Developmental Biology describe the mathematical
principle underlying observed levels of gene
expression. They used information from public
databases of whole genome sequences and from their own
microarray analyses. Proportional dynamics, also known
as .rich-travel-more,. showed that power law levels of
gene expression were observed not only in different
organisms, but also within discrete organs or at
specific developmental times in the same organism
(PNAS, DOI:10.1073/pnas.0306244101, March 1, 2004).
The team examined how genes change their expression in
different conditions and observed that highly
expressed genes change more, while genes expressed
infrequently change less. .It's proportional; the
magnitude of change[s] are proportional to their
expression levels,. said Ueda. .I also found [that]
proportional dynamics can reproduce the complex
pattern of distribution in gene expression
levels.called power law distribution..
Ueda said he was surprised to find Escherichia coli
and humans are governed by the same simple mechanism.
.I am glad to have found a simple and universal
mechanism that exists in all systems of life,. he told
The Scientist.
Plotting the distribution of different gene expression
levels against the expression hierarchy of those genes
results in a straight line. .I unexpectedly found that
distribution[s] of gene expression were heterogeneous
and governed by the power law of minus 2 exponent,. he
told The Scientist in an E-mail.
Yutaka Suzuki, research scientist at the Institute of
Medical Science Human Genome Center explained, .In
every case, you can see the straight line in the
scattering plot. The basic concept is that such a kind
of law is conserved between cell types and organisms
in many kinds of context..
Suzuki, who was not involved in the study, explained
that it is the ratio of minus 2 that is conserved.
.That's the universal observation, that's the point of
this manuscript,. he said.
Lada Adamic, a power law expert in the Information
Dynamics Laboratory at Hewlett-Packard, told The
Scientist that although she was not a biologist, she
would almost expect this observation because these
distributions are extremely common. .As long as you
have like a multiplicative process.which is what this
is, this proportional process.you're going to end up
with a distribution like that,. she said.
Adamic, who was not involved in the study, said that
the same distribution was actually observed by Yule in
1913 when he was looking at the abundance of species
in different genera. .So that's kind of like a
biological thing,. she said. .The problem with power
laws is that people keep kind of rediscovering them..
.I myself have heard that this behavior of a system is
very universal, [but] this is the first groundwork for
this kind of analysis as I believe it. For biological
systems, this is a first, so in that sense at least I
think this is significant,. Suzuki said.
Ueda said that in the future, statistical analysis
utilizing this .proportional. dynamics would be useful
for the analysis of microarray data in any organism.
.Statistical analysis based on .proportional. dynamics
can be applied to the search for the significantly
changed genes in two conditions,. he said in an
E-mail. .We are preparing the manuscript on this type
of application..
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Certified Health Physicist
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