Home' Technology Review : January 2005 Contents TECHNOLOGY REVIEW
dropper. However, if a given bit of information requires more
than one photon, the message can be intercepted without being
detected. Consequently, the laser in a quantum encryption sys-
tem must reliably convert an electrical pulse into a single photon
at a prescribed wavelength. This work falls short of that goal, as
it converts each electrical input into multiple photons. But it is an
important step toward building new photon sources for optical
Source: Park, H. G. et al. (2004) Electrically driven single-cell photonic crystal laser.
Distant DNA controls gene activity
: Even in cases where two people share the same gene,
they can produce widely di ering amounts of the protein the
gene codes for. This can lead to di erences in physical character-
istics, and it can also mean the di erence between sickness and
health. Segments of DNA called regulatory elements are one fac-
tor controlling how much of a particular protein the body pro-
duces. While researchers today can use algorithms to pick out
genes from sequences of DNA, they have previously been unable
to accurately distinguish regulatory elements from other non-
coding DNA, let alone match those elements with the genes that
they regulate. Researchers at the University of Pennsylvania, led
by Vivian Cheung, have found a way to do just that.
: Using white blood cells from 94 people,
the researcher s identi ed more tha n 3,500 genes whose ex-
pression wa s simila r among relatives but va ried widely a mong
people who were unrelated. These patterns of expression were
then correlated with patterns of known genetic markers across
thegenome.Hundreds ofgenes expression waslinkedtopar-
tic ular genetic ma rker s---fa r more tha n the number predicted
by cha nce. About four - fths of these ma rkers were loc ated
more than 5,000 base pairs from the genes that they regulated;
ma ny were even on other chromosomes. Resea rchers fou nd
that some "hot spot" regions apparently in uence the expres-
sion ofmorethan30genes.In addition, manygenes seemtobe
regulated by more than one region.
: Researchers can nally study the genetic dif-
ferences gover ning gene expression. The hot spots, which
Cheung s team calls "master regulators," will help to tease
out some of the mysteries that sur round gene expression.
Mor e immediately, the techniques may allow researchers to
use variation within genes and within regulatory elements to
u ndersta nd a nd treat disease. For yea r s, geneticists have
scou red the hu man genome for genes that contribute to com-
plex traits, like susceptibility to depression or heart disea se.
Finding factors that control the genes is just as important but
much more di cult. Now scientists should be better equipped
to nd the genetic variations that make a di erenc e in matter s
of life and death.
Source: Morley, M. et al. (2004) Genetic analysis of genome-wide variation in
human gene expression. Nature 430:743-7.
On Again, O Again
A gene comes with a handy switch
: Good health requires more tha n the right genes;
those genes must also be able to switch on and o at the right
time. In research involving a nimals or cell cultures, guring
out a gene s function is much easier when scientists can turn it
on at will. Led by Richard Mulligan, a group of researchers at
Ha r vard Medical School a nd Children s Hospital in Boston
have crafted genes that come with an easily controlled on/o
switch---a powerful resea rch tool that has the potential to o er
a new kind of gene therapy.
: The switch consists of a ribozyme, an en-
zyme made up of RNA. Laising Yen, a postdoc in Mulligan s lab,
and colleagues inserted a ribozyme sequence into a gene that
coded for an easily detectable protein. Cells with the altered gene
made long stretches of messenger RNA; part of the RNA made
the ribozyme, while the rest carried instructions for making the
protein. The researchers tinkered with di erent ribozymes,
eventually creating ones that were able to chop up the RNA before
the protein it coded for could be made. In the cell cultures and liv-
ing mice containing the ribozyme sequence, protein production
dropped to nearly undetectable levels. What s more, the re-
searchers were able to deactivate the ribozyme using certain
drugs---essentially turning on the inserted gene by turning o the
o switch. Such treatments succeeded in restoring gene expres-
sion by up to 50 percent.
: The researcher s imagine c reating genetic
therapies in which the onset of a physiological condition would
activate the genes necessary to manage it. Genetically engi-
neered cells might be able to secrete insulin in accorda nc e with
glucose levels, freeing diabetic s from consta nt blood monitor -
ing a nd insulin injection. For the moment, however, such
dreams are far from reality. Closer at hand and still very excit-
ing a re discovery techniques that would allow researcher s to
monitor the e ects produced by several genes in a single ani-
mal, or to analyze how a gene adjusts to an organism s aging or
to di erent stages of a disea se.
Source: Yen, L. et al. (2004) Exogenous control of mammalian gene expression
through modulation of RNA self-cleavage. Nature 431:471-6.
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