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Science Forum Index » Bio Evolution Forum » Special Issue: Freedom of Expression
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| Robert Karl Stonjek |
 Posted: Fri Mar 28, 2008 8:01 am |
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Science 28 March 2008:
Vol. 319. no. 5871, p. 1781
DOI: 10.1126/science.319.5871.1781
Introduction to special issue
Freedom of Expression
Guy Riddihough, Beverly A. Purnell, John Travis
As in civil society, where there must necessarily be checks and balances on
freedom of expression, cells have evolved a range of mechanisms to regulate
the expression of their constituent genes. By far the best-understood medium
for gene regulation is the protein transcription factor. The broad set of
rules by which these regulators operate is outlined by Hobert (p. 1785).
However, new and unexpected gene regulatory systems have been discovered in
the past decade, perhaps the most important of which involve microRNAs
(miRNAs). Hobert compares the action of these small noncoding RNAs, found in
many eukaryotes, with their proteinaceous counterparts, showing that miRNAs
share many similar activities but also display unique traits in their
compartmentalization, rapid reversibility, and evolvability. Makeyev and
Maniatis (p. 1789) provide examples of the profound systemwide influence
that miRNAs can have on gene expression programs. miRNAs are also being
linked to a growing list of common ailments, including cancer, heart
disease, diabetes, and viral illnesses such as hepatitis. In a related News
story (p. 1782), Jennifer Couzin explores how miRNAs are attracting the
interest of biomedical researchers and biotechnology companies eager for new
ways to diagnose and treat diseases.
Another recently discovered RNA-based regulatory system is the riboswitch,
found in plant, fungal, and prokaryotic RNAs. Although they possess a
deceptively simple bipartite structure, Breaker (p. 1795) describes how
their chemistry, conformation, and kinetics have facilitated the evolution
of sophisticated gene-control systems. Indeed, the overwhelming regulatory
potential of RNA is graphically described by Amaral et al. (p. 1787), who
list the many and varied instances in which RNA has been implicated in
regulatory events.
This is not to suggest that research on transcription factors is
moribund--far from it, as revealed by Core and Lis (p. 1791), for example,
who discuss the revival of earlier work revealing a critical regulatory
step, the pausing of the RNA polymerase II molecule, during the early phase
of transcription elongation. The often highly dispersed nature of
transcription factor binding sites in many eukaryotic genes provided the
first clues that the spatial organization of the genome can be critical for
gene regulation; for example, allowing combinatorial interactions between
genes and regulatory elements, as described by Dekker (p. 1793).
Understanding the origins of these regulatory systems requires that we
examine how they have evolved, prompting Tuch et al. (p. 1797) to note that
orthologous regulatory circuits with similar transcriptional outputs can
nonetheless undergo massive rewiring in even closely related species.
Several gene regulatory systems are also highlighted in our online sister
journal Science Signaling (www.sciencemag.org/generegulation/): how
oncogenic Ras causes the epigenetic silencing of Fas and other
tumor-suppressor genes, how intrachromosomal looping positions enhancers
close to the promoter of the tumor necrosis factor-gene to stimulate its
expression in activated T cells, and how the abundance of the
transcriptional coactivator steroid receptor coactivator-3 controls
estrogen-dependent gene transcription.
Source: Science (Includes video presentation)
319.5871.1781
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Robert Karl Stonjek |
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