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This Week in SCIENCE, Volume 311, Issue 5769,
dated March 31 2006, is now available at:
http://www.sciencemag.org/content/vol311/issue5769/twis.dtl
A plain-text copy of the "This Week in SCIENCE" section has been
appended below.
-----------------------------------------------------------------
This Week in SCIENCE
March 31 2006, 311 (5769)
THIS WEEK IN SCIENCE
--------------------
---------------------------------------------------------------------------
Ancient Tropical Forest Diversity
---------------------------------------------------------------------------
Understanding how the high plant species diversity of tropical forests
arose has been hampered by the scant fossil evidence of lowland tropical
rainforest species diversity in the geological record. Jaramillo et al. (p.
1893) now present a 45-million-year time series of plant diversity in the
Neotropics with an unparalleled resolution. Changes in tropical-biome area
were the main factor driving local tropical diversity. The observed
diversity pattern resembled reconstructed global temperatures, which
suggests that global climate mediated the change in tropical-biome area.
Past episodes of climate warming have driven local speciation by increasing
the area of tropical-like climate. Global cooling, however, drove local
extinction by reducing the tropical-like area.
CREDIT: JARAMILLO AND RUEDA, 2006
---------------------------------------------------------------------------
Fast Spinning
---------------------------------------------------------------------------
Pulsars are fast-spinning neutron stars that emit flashing twin radio
beams. For the last 23 years, the speed limit was set by the first such
pulsar discovered, which rotates at 642 hertz. Hessels et al. (p. 1901,
published online 12 January; see the Perspective by Grindlay) have now
found an even faster pulsar that spins 716 times a second. This extreme
pulsar was found with the giant Green Bank Telescope during a survey of the
globular cluster Terzan 5. From the pulsar's rotation speed, the star's
diameter is calculated to be less than 16 kilometers, and limits can be
placed on mechanisms for braking of the system by gravitation radiation.
The faintness of this pulsar suggests that even faster ones await
discovery.
---------------------------------------------------------------------------
Up in the Middle
---------------------------------------------------------------------------
Meteorological observations show that surface temperature of the western
side of the Antarctic Peninsula has increased at a rate faster than that of
any other region on Earth in the last 50 years. However, there have been
few statistically significant surface temperature changes across the rest
of Antarctica, which may even have cooled slightly in some places during
recent decades. In order to help provide a more complete picture of how
temperatures in the Antarctic troposphere have changed, Turner et al. (p.
1914) examined recently released radiosonde data from 1971 to 2003. The
Antarctic middle troposphere has warmed by 0.5{degrees}C or more per decade
during the winters during that time. Although this rise has been detected,
its cause is still unknown.
CREDIT: TURNER ET AL.
---------------------------------------------------------------------------
Uplifting Off Sumatra
---------------------------------------------------------------------------
Rupture of the Sunda megathrust during the giant earthquake of 28th March
2005 with a moment magnitude of 8.7 produced spectacular tectonic
deformation along a 400-kilometer strip of the western Sumatran
archipelago. Briggs et al. (p. 1897; see the Perspective by Bilham) combine
measurements of uplifted coral and continuous satellite records to map the
pattern of deformation in the region. They reveal belts of uplift as high
as 2.9 meters parallel to the trench and a 1-meter-deep subsidence trough
between the islands and main Sumatran coast. Two barriers to the
propagation of this earthquake are identified.
---------------------------------------------------------------------------
Frictionless Spinning
---------------------------------------------------------------------------
One of the principal changes in moving a chemical system from the gas to
solution phase is a huge increase in collision frequency. Constant
bombardment by solvent molecules tends to quickly equilibrate any excess
energy that a solute may acquire, for example, by photoexcitation. Moskun
et al. (p. 1907) show that if a solute is given a sufficient burst of
angular momentum, it can transiently push aside the surrounding solvent and
rotate for picoseconds as if it were in a collisionless gas phase
environment. Rapidly spinning CN fragments were generated with specific
energies by ultraviolet photolysis of ICN in alcohol or aqueous solution.
The persistent coherent rotation was well reproduced by simulating CN
rotors in liquid argon, which suggests that solvent structure had little
impact on the initial phase of nearly frictionless spinning.
---------------------------------------------------------------------------
High-Performance Superconducting Wires
---------------------------------------------------------------------------
Potential applications of high-temperature superconductors have included
high-efficiency power transmission and levitating trains. However, these
applications require wires that can carry huge currents and still remain
superconducting in high magnetic fields. Kang et al. (p. 1911; see the news
story by Service) have fabricated so-called second-generation
superconducting wires, flexible metal substrates coated with thick
high-temperature superconducting material, and show that they can meet the
performance targets that have been set by industry for many applications.
---------------------------------------------------------------------------
Drying Streams
---------------------------------------------------------------------------
Africa is particularly vulnerable to the tragic consequences of drought,
and climate models project that the mean annual rainfall in the northern
and southern sections of the continent will decrease significantly during
this century. De Wit and Stankiewicz (p. 1917, published online 2 March)
examine what effects these expected changes in precipitation will have on
perennial stream flow using a continent-wide database of all of the rivers
and lakes in Africa and the fields of precipitation projected by a
collection of climate change models. Perennial drainage could be
significantly reduced in 25% of Africa by the end of the century, which
would place an even greater burden on already struggling populations.
---------------------------------------------------------------------------
Highlighting the Niche
---------------------------------------------------------------------------
Replenishment of hair, skin, mucosal surfaces, and blood all depend on a
steady supply of replacement cells that are generated by a small population
of quiet but dedicated stem cells. These sorts of stem cells seem to reside
in particular physical locations, or niches, within the organism. Moore and
Lemischka (p. 1880) now review stem cell niches, including what they look
like and how they direct the function of the stem cells, and also explore
some of the questions about them that remain open.
---------------------------------------------------------------------------
Kaposi's Virus Entry Receptor
---------------------------------------------------------------------------
Kaposi's sarcoma-associated herpes virus (KSHV) is responsible for causing
the debilitating life-threatening lesions often observed in patients with
HIV/AIDS. Kaleeba and Berger (p. 1921) now identify human xCT, the light
chain of human cystine/glutamate transporter as a receptor for the virus
necessary and sufficient for its entry into target cells. Recombinant xCT
rendered otherwise nonpermissive target cells susceptible to KSHV
glycoprotein-mediated cell fusion and to KSHV virion entry, and antibodies
to CT blocked KSHV fusion and entry with naturally permissive target cells.
---------------------------------------------------------------------------
A Mitotic Function for Lamin B
---------------------------------------------------------------------------
Nuclear lamins line the nuclear envelope to make up the nuclear lamina,
which helps to maintain the structure and function of the nucleus. During
cell division, the nuclear lamina disassembles, and the role for the
lamins, if any, in mitosis is unclear. Tsai et al. (p. 1887, published
online 16 March) now show that lamin B is required for the formation of the
mitotic spindle. In cell extracts, lamin B formed a matrix with which
spindle-assembly factors (which promote assembly of microtubules) were
associated. Thus, lamin B is a key part of the so-called "spindle matrix,"
a structure known to be associated with assembly of the spindle but whose
molecular constituents have not been described.
CREDIT: TSAI ET AL.
---------------------------------------------------------------------------
Accentuate the Positive
---------------------------------------------------------------------------
The cytokine interleukin-2 (IL-2) facilitates proliferation of naive T
cells, but several studies have shown that antibodies that bind IL-2, which
at first glance should be inhibitory, can promote the expansion of subsets
of memory CD8 T cells. Thus, IL-2 somehow might inhibit suppressive T cell
populations that would otherwise prevent memory CD8 T cell expansion.
Boyman et al. (p. 1924, published online 16 February; see the Perspective
by Prlic and Bevan) now show that instead, binding of antibodies to IL-2
augments the direct activity of the cytokine on memory CD8 T cells
themselves. Immune complexes form that focus local levels of IL-2 through
presentation by Fc receptors. These observations could be important to
consider in therapies that involve the manipulation of IL-2 and other
cytokines, such as bone marrow transplantation and tumor immunotherapy.
---------------------------------------------------------------------------
Keeping the Wheat Near the Chaff
---------------------------------------------------------------------------
Wild grasses tend to release their mature seed fairly easily to facilitate
widespread propagation. Domesticated grasses, such as wheat, rice, maize,
and oat crops, do not release their grain as easily, and indeed would be of
little value if the grain were to fall willy-nilly to the ground. Li et al.
(p. 1936; see the cover and the Brevia by Tanno and Willcox) describe a
one-nucleotide substitution in a rice gene that encodes a putative
transcription factor that appears to account for this difference. The gene
is expressed late in grain development at the junction between the seed and
the mother plant.
---------------------------------------------------------------------------
The Making of Complex Carbohydrates
---------------------------------------------------------------------------
The cell walls of grasses differ from those of other plants in that they
contain a particular type of polysaccharide, glucan. Burton et al. (p.
1940; see the Perspective by Keegstra and Walton) have now identified the
(1,3;1,4)--D-glucan synthase genes of rice, which are critical for
production of the grain-specific glucan. The rice gene was identified by
comparison with quantitative trait loci of barley that affect its malt
quality. Improved understanding of the complex carbohydrate biochemistry
behind cell walls could lead to modifications tailored for specific
purposes, whether as fuel, food, or fiber.
---------------------------------------------------------------------------
Six in a Row
---------------------------------------------------------------------------
Among the many unusual properties of carbon, relative to the other
elements, is its propensity to catenate into one-dimensional chains. Hill
et al. (p. 1904) find that-diketiminate ligands can coax indium to form a
chain as well, in contrast to the more common tendency of this metallic
element to form bridged clusters. Crystallography revealed a partially
coiled string of six indium centers, each coordinated by a-diketiminate
ligand, with the ends capped by iodides. Spectroscopy and theoretical
modeling offer preliminary evidence for electron delocalization along
the-bonded In backbone.
---------------------------------------------------------------------------
Shared Signals
---------------------------------------------------------------------------
The immune system is classically described in terms of innate and acquired
immunity, although it is becoming increasingly apparent that these two arms
share some fundamental cellular and molecular processes. In large part,
this overlap exists "downstream" at points of gene expression and
transcriptional regulation; for example, the transcription factor NFB
activates a large number of innate and acquired immune response genes.
Although "upstream" (membrane proximal) signaling proteins appear to be
more segregated, Suzuki et al. (p. 1927) find that IRAK-4, a dominant
protein kinase already known to be involved in signaling innate immune
responses from Toll-like receptors, also supports signaling from the T cell
receptor. Thus, mice lacking the IRAK-4 gene showed diminished acquired T
cell immunity to viral infection.
---------------------------------------------------------------------------
Finding Variation
---------------------------------------------------------------------------
It is no longer enough to have one sequenced genome of an organism;
characterizing function and understanding diversity or evolution can
require inefficient and expensive resequencing efforts. Gresham et al. (p.
1932, published online 9 March) have compared an entire yeast genome to a
reference sequence represented on a microarray to rapidly locate all
sequence differences. Genomes could differ by as little as one mutation or
as many as 30,000. The approach was used for identifying genes related to
specific traits and to track all the single-nucleotide polymorphisms that
accumulate during experimental evolution of a yeast population.
-----------------------------------------------------------------
dated March 31 2006, is now available at:
http://www.sciencemag.org/content/vol311/issue5769/twis.dtl
A plain-text copy of the "This Week in SCIENCE" section has been
appended below.
-----------------------------------------------------------------
This Week in SCIENCE
March 31 2006, 311 (5769)
THIS WEEK IN SCIENCE
--------------------
---------------------------------------------------------------------------
Ancient Tropical Forest Diversity
---------------------------------------------------------------------------
Understanding how the high plant species diversity of tropical forests
arose has been hampered by the scant fossil evidence of lowland tropical
rainforest species diversity in the geological record. Jaramillo et al. (p.
1893) now present a 45-million-year time series of plant diversity in the
Neotropics with an unparalleled resolution. Changes in tropical-biome area
were the main factor driving local tropical diversity. The observed
diversity pattern resembled reconstructed global temperatures, which
suggests that global climate mediated the change in tropical-biome area.
Past episodes of climate warming have driven local speciation by increasing
the area of tropical-like climate. Global cooling, however, drove local
extinction by reducing the tropical-like area.
CREDIT: JARAMILLO AND RUEDA, 2006
---------------------------------------------------------------------------
Fast Spinning
---------------------------------------------------------------------------
Pulsars are fast-spinning neutron stars that emit flashing twin radio
beams. For the last 23 years, the speed limit was set by the first such
pulsar discovered, which rotates at 642 hertz. Hessels et al. (p. 1901,
published online 12 January; see the Perspective by Grindlay) have now
found an even faster pulsar that spins 716 times a second. This extreme
pulsar was found with the giant Green Bank Telescope during a survey of the
globular cluster Terzan 5. From the pulsar's rotation speed, the star's
diameter is calculated to be less than 16 kilometers, and limits can be
placed on mechanisms for braking of the system by gravitation radiation.
The faintness of this pulsar suggests that even faster ones await
discovery.
---------------------------------------------------------------------------
Up in the Middle
---------------------------------------------------------------------------
Meteorological observations show that surface temperature of the western
side of the Antarctic Peninsula has increased at a rate faster than that of
any other region on Earth in the last 50 years. However, there have been
few statistically significant surface temperature changes across the rest
of Antarctica, which may even have cooled slightly in some places during
recent decades. In order to help provide a more complete picture of how
temperatures in the Antarctic troposphere have changed, Turner et al. (p.
1914) examined recently released radiosonde data from 1971 to 2003. The
Antarctic middle troposphere has warmed by 0.5{degrees}C or more per decade
during the winters during that time. Although this rise has been detected,
its cause is still unknown.
CREDIT: TURNER ET AL.
---------------------------------------------------------------------------
Uplifting Off Sumatra
---------------------------------------------------------------------------
Rupture of the Sunda megathrust during the giant earthquake of 28th March
2005 with a moment magnitude of 8.7 produced spectacular tectonic
deformation along a 400-kilometer strip of the western Sumatran
archipelago. Briggs et al. (p. 1897; see the Perspective by Bilham) combine
measurements of uplifted coral and continuous satellite records to map the
pattern of deformation in the region. They reveal belts of uplift as high
as 2.9 meters parallel to the trench and a 1-meter-deep subsidence trough
between the islands and main Sumatran coast. Two barriers to the
propagation of this earthquake are identified.
---------------------------------------------------------------------------
Frictionless Spinning
---------------------------------------------------------------------------
One of the principal changes in moving a chemical system from the gas to
solution phase is a huge increase in collision frequency. Constant
bombardment by solvent molecules tends to quickly equilibrate any excess
energy that a solute may acquire, for example, by photoexcitation. Moskun
et al. (p. 1907) show that if a solute is given a sufficient burst of
angular momentum, it can transiently push aside the surrounding solvent and
rotate for picoseconds as if it were in a collisionless gas phase
environment. Rapidly spinning CN fragments were generated with specific
energies by ultraviolet photolysis of ICN in alcohol or aqueous solution.
The persistent coherent rotation was well reproduced by simulating CN
rotors in liquid argon, which suggests that solvent structure had little
impact on the initial phase of nearly frictionless spinning.
---------------------------------------------------------------------------
High-Performance Superconducting Wires
---------------------------------------------------------------------------
Potential applications of high-temperature superconductors have included
high-efficiency power transmission and levitating trains. However, these
applications require wires that can carry huge currents and still remain
superconducting in high magnetic fields. Kang et al. (p. 1911; see the news
story by Service) have fabricated so-called second-generation
superconducting wires, flexible metal substrates coated with thick
high-temperature superconducting material, and show that they can meet the
performance targets that have been set by industry for many applications.
---------------------------------------------------------------------------
Drying Streams
---------------------------------------------------------------------------
Africa is particularly vulnerable to the tragic consequences of drought,
and climate models project that the mean annual rainfall in the northern
and southern sections of the continent will decrease significantly during
this century. De Wit and Stankiewicz (p. 1917, published online 2 March)
examine what effects these expected changes in precipitation will have on
perennial stream flow using a continent-wide database of all of the rivers
and lakes in Africa and the fields of precipitation projected by a
collection of climate change models. Perennial drainage could be
significantly reduced in 25% of Africa by the end of the century, which
would place an even greater burden on already struggling populations.
---------------------------------------------------------------------------
Highlighting the Niche
---------------------------------------------------------------------------
Replenishment of hair, skin, mucosal surfaces, and blood all depend on a
steady supply of replacement cells that are generated by a small population
of quiet but dedicated stem cells. These sorts of stem cells seem to reside
in particular physical locations, or niches, within the organism. Moore and
Lemischka (p. 1880) now review stem cell niches, including what they look
like and how they direct the function of the stem cells, and also explore
some of the questions about them that remain open.
---------------------------------------------------------------------------
Kaposi's Virus Entry Receptor
---------------------------------------------------------------------------
Kaposi's sarcoma-associated herpes virus (KSHV) is responsible for causing
the debilitating life-threatening lesions often observed in patients with
HIV/AIDS. Kaleeba and Berger (p. 1921) now identify human xCT, the light
chain of human cystine/glutamate transporter as a receptor for the virus
necessary and sufficient for its entry into target cells. Recombinant xCT
rendered otherwise nonpermissive target cells susceptible to KSHV
glycoprotein-mediated cell fusion and to KSHV virion entry, and antibodies
to CT blocked KSHV fusion and entry with naturally permissive target cells.
---------------------------------------------------------------------------
A Mitotic Function for Lamin B
---------------------------------------------------------------------------
Nuclear lamins line the nuclear envelope to make up the nuclear lamina,
which helps to maintain the structure and function of the nucleus. During
cell division, the nuclear lamina disassembles, and the role for the
lamins, if any, in mitosis is unclear. Tsai et al. (p. 1887, published
online 16 March) now show that lamin B is required for the formation of the
mitotic spindle. In cell extracts, lamin B formed a matrix with which
spindle-assembly factors (which promote assembly of microtubules) were
associated. Thus, lamin B is a key part of the so-called "spindle matrix,"
a structure known to be associated with assembly of the spindle but whose
molecular constituents have not been described.
CREDIT: TSAI ET AL.
---------------------------------------------------------------------------
Accentuate the Positive
---------------------------------------------------------------------------
The cytokine interleukin-2 (IL-2) facilitates proliferation of naive T
cells, but several studies have shown that antibodies that bind IL-2, which
at first glance should be inhibitory, can promote the expansion of subsets
of memory CD8 T cells. Thus, IL-2 somehow might inhibit suppressive T cell
populations that would otherwise prevent memory CD8 T cell expansion.
Boyman et al. (p. 1924, published online 16 February; see the Perspective
by Prlic and Bevan) now show that instead, binding of antibodies to IL-2
augments the direct activity of the cytokine on memory CD8 T cells
themselves. Immune complexes form that focus local levels of IL-2 through
presentation by Fc receptors. These observations could be important to
consider in therapies that involve the manipulation of IL-2 and other
cytokines, such as bone marrow transplantation and tumor immunotherapy.
---------------------------------------------------------------------------
Keeping the Wheat Near the Chaff
---------------------------------------------------------------------------
Wild grasses tend to release their mature seed fairly easily to facilitate
widespread propagation. Domesticated grasses, such as wheat, rice, maize,
and oat crops, do not release their grain as easily, and indeed would be of
little value if the grain were to fall willy-nilly to the ground. Li et al.
(p. 1936; see the cover and the Brevia by Tanno and Willcox) describe a
one-nucleotide substitution in a rice gene that encodes a putative
transcription factor that appears to account for this difference. The gene
is expressed late in grain development at the junction between the seed and
the mother plant.
---------------------------------------------------------------------------
The Making of Complex Carbohydrates
---------------------------------------------------------------------------
The cell walls of grasses differ from those of other plants in that they
contain a particular type of polysaccharide, glucan. Burton et al. (p.
1940; see the Perspective by Keegstra and Walton) have now identified the
(1,3;1,4)--D-glucan synthase genes of rice, which are critical for
production of the grain-specific glucan. The rice gene was identified by
comparison with quantitative trait loci of barley that affect its malt
quality. Improved understanding of the complex carbohydrate biochemistry
behind cell walls could lead to modifications tailored for specific
purposes, whether as fuel, food, or fiber.
---------------------------------------------------------------------------
Six in a Row
---------------------------------------------------------------------------
Among the many unusual properties of carbon, relative to the other
elements, is its propensity to catenate into one-dimensional chains. Hill
et al. (p. 1904) find that-diketiminate ligands can coax indium to form a
chain as well, in contrast to the more common tendency of this metallic
element to form bridged clusters. Crystallography revealed a partially
coiled string of six indium centers, each coordinated by a-diketiminate
ligand, with the ends capped by iodides. Spectroscopy and theoretical
modeling offer preliminary evidence for electron delocalization along
the-bonded In backbone.
---------------------------------------------------------------------------
Shared Signals
---------------------------------------------------------------------------
The immune system is classically described in terms of innate and acquired
immunity, although it is becoming increasingly apparent that these two arms
share some fundamental cellular and molecular processes. In large part,
this overlap exists "downstream" at points of gene expression and
transcriptional regulation; for example, the transcription factor NFB
activates a large number of innate and acquired immune response genes.
Although "upstream" (membrane proximal) signaling proteins appear to be
more segregated, Suzuki et al. (p. 1927) find that IRAK-4, a dominant
protein kinase already known to be involved in signaling innate immune
responses from Toll-like receptors, also supports signaling from the T cell
receptor. Thus, mice lacking the IRAK-4 gene showed diminished acquired T
cell immunity to viral infection.
---------------------------------------------------------------------------
Finding Variation
---------------------------------------------------------------------------
It is no longer enough to have one sequenced genome of an organism;
characterizing function and understanding diversity or evolution can
require inefficient and expensive resequencing efforts. Gresham et al. (p.
1932, published online 9 March) have compared an entire yeast genome to a
reference sequence represented on a microarray to rapidly locate all
sequence differences. Genomes could differ by as little as one mutation or
as many as 30,000. The approach was used for identifying genes related to
specific traits and to track all the single-nucleotide polymorphisms that
accumulate during experimental evolution of a yeast population.
-----------------------------------------------------------------
