H I G H L I G H T S O F T H E R E C E N T L I T E R AT U R E

EDITORS’ CHOICE
edited by Stella HurtleyE C O L O G Y / E VO L U T I O N

Butterfly Mate Recognition
In butterflies, the elaborate and colorful wing patterns have a number of functions, including warning signals to predators, camouflage,
and thermoregulation. In many species
they also serve as mate recognition
Wing patterns
signals. However, in some groups ofof female Lycaeides idas
butterflies the differences(below) and L.
in wing pattern between
melissa (left).
species, or between populations within a species,
are slight and subtle, and insuch cases a mate recognition function has beenthought unlikely. Fordyce et al. studied
the ability of two closely related species
with very similar wing patterns in thefamily Lycaenidae (blues and hairstreaks)
to recognize their conspecifics. Males werepresented with choices of females from different populations, including accurate computer-generated paper
models of females to exclude the possibility of other cues such as
pheromones. They preferred to initiate courtship with females ormodels having the conspecific wing pattern, indicating that evenslight differences are distinguishable. Manipulation of the computergenerated models has the potential to suggest which elements of
the wing pattern are most significant in mate recognition. — AMS
J. Evol. Biol. 15, 871 (2002).

DEVELOPMENTCREDITS: FORDYCE ET AL., J. EVOL. BIOL. 15, 871 (2002)

Getting Your Left
Right
Left-right asymmetry—whereby, for example, the heart is on
the left side of the body withfunctionally distinct left andright chambers—is establishedvery early in development. In
the African toad Xenopus, and inchick embryos, Levin et al. now
show that the H+ and K+ ATPasetransporter is required in theformation of embryos with anormal left-right body axis. In
fertilized Xenopus eggs, maternal transporter messenger RNA
is symmetrically expressed;
however, during the first twocell divisions of development it
becomes localized. In chick embryos the transporter mRNAs
are again symmetrically localized, but a difference in membrane potential is generated either side of the primitive streak.

In both systems, interfering withtransporter activity caused randomization of the expression
pattern of asymmetrically expressed genes, resulting in opposite handedness in the organs
and tissues produced later indevelopment—including theheart, the gut, and the gall bladder. Thus, very early in development, differential ion fluxes
generated by the H+/K+ ATPaseare key to determining future
left-right asymmetry. — SMH
Cell 111, 77 (2002).

APPLIED PHYSICSA New Low for Photonic Crystal Lasers
The development of integrated
optical technology places strict
demands on its components,
including the ability to guide,
modulate, and detect light efficiently. The ideal device would
also have small volume and becompatible with current semiconductor technology processing. Photonic crystals, whichcontain arrays of periodicallyvarying dielectric contrast thatcan be tuned to transmit particular wavelengths, are promising materials for meeting all of
the above criteria. As a demonstration of their potential, Loncar et al. describe the fabrication and operation at room
temperature of a high–quality
factor, low-threshold photonic
crystal laser etched into a slabof InGaAsP. With a spot size ofjust 3.9 square micrometers,
lasing from the structure
begins at just 220 microwattsof input light power, a threshold
power significantly lower
than other quantum
well–based lasers. — ISOAppl. Phys. Lett. 81, 2680 (2002).

AT M O S P H E R I C S C I E N C E

Certainly Warmer
How much global warming occurs as a result of human additions of radiatively active
agents like greenhouse gases
and sulfate aerosols depends
on how sensitive climate is tothese species. “Climate sensitivity” is a measure of how
much global average surface
temperature can be expected
to change in response to an increase in radiative forcing
equivalent to that which
would be produced by doubling the concentration of atmospheric CO2 from pre-industrial levels (280 ppm). The
best estimates of climate sensitivity suggest that its value
lies between 1.5° and 4.5°C,
but they do not generally include any information about
how certain those bounds are.
Gregory et al. use a model that
includes observations of temperature changes in the ocean
and the atmosphere to evaluate the probable lower boundof climate sensitivity, and findthat there is a 95% chancethat it is at least 1.6°C. Thus,
unless greenhouse gas emissions are abated, substantial
climate change will occur in
response to warming during
the next century. The large uncertainty in the amount of radiative forcing prevents the determination of an upper boundfor climate sensitivity. — HJS
J. Clim. 15, 3117 (2002).

GENETICSRNAi and Fragile X
Fragile X syndrome is the mostcommon form of inheritedmental retardation and is generally caused by mutations in
the fragile X mental retardation
gene (FMR1). The FMR1 protein
is thought to negatively regulate the translation of specificgenes. Caudy et al. and Ishizuka
et al. have now demonstrated
that the homologous protein in
Drosophila, dFMRP, is associated with a vital component of
the RNA interference (RNAi)
machinery, the RNA-induced
silencing complex (RISC), as
well as with ribosomal proteins
and VIG (Vasa intronic gene).
These results suggest that RISC
might provide a link between
RNAi-based and FMRP-basedmodes of post-transcriptional
gene control or, more provocatively, that FMRP may play arole in RNAi, thereby implicating defects in RNAi in humandisease. — GR
Genes Dev. 16, 2491; 2497 (2002).

GEOPHYSICS

Dynamic
Disappointment
Near-surface horizontal tectonics have shaped much ofEarth’s topography; many sedimentary basins, for instance,
apparently stemmed from horizontal stretching of the lithosphere, followed by cooling,subsidence, and sedimentary
infilling. However, some theoretical models have concluded
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that a substantial part of Earth’s surfacetopography might be tied to density-driven flow in the mantle. For example, thesubduction of cool, dense slabs in themantle, viscously coupled to the overlying
lithosphere, could “pull down” Earth’s surface—by as much as 1 to 2 km. The possibility of such dynamic topography has
profound implications for how we understand basin formation, but determining
subsidence contribution in real sedimentary basins has been difficult.
Wheeler and White analyzed age,depth, and sedimentary thickness datafrom wells, seismic reflection profiles, andother sources over a wide area of Southeast Asia, where models have predicted
some of the largest amplitudes of dynamic topography on Earth. The maximum
basin depth that could potentially be explained by dynamic topography amounts
to around 300 m, far less than the 1 to 2
km predicted by numerical models. — SW
Tectonics 10.1029/2001TC900023 (2002).

M AT E R I A L S S C I E N C E

Nanotubes in the Groove
Molecules in liquid crystalline materials can bealigned either by pretreatment of a substratesurface or by the subsequent application of anelectric or magnetic field.
Experimental setup (top)and resulting electric fieldalignment of the carbon
nanotubes (bottom).

Lynch and Patrick
exploited thisproperty to create well-oriented carbon
nanotube(CNT) films.
Orient with magnetic or
The CNTs were electric field, or substratedissolved into
one of two common
nematic liquid
crystals andthen deposited
onto prescratchedpolycarbonate membrane
Draw solution through pores
substrates. The
liquid crystal
molecules
tended toalign parallelto thegrooves in the substrate, forcing the CNT
to follow suit. By applying a mild vacuum,
the liquid crystal was drawn out throughthe holes in the membrane, leaving behindeither single or multilayered films as desired. Applying an electricfield to part of the substrate
could locally reorient someof the CNTs perpendicular tothe direction of the grooves.
This technique should makeit easier to engineer nanotube-based devices or reinforcing layers without theneed to grow oriented CNT
in situ. — MSL
Nano Lett. 10.1021/nl025694j (2002).

H I G H L I G H T E D I N S C I E N C E ’ S S I G N A L T R A N S D U C T I O N K N OW L E D G E E N V I RO N M E N T

Modeling Fine-Tuned Affinity
Using a combination of experimental analysis and mathematicalmodeling, Coombs et al. have investigated the fundamental
molecular interactions by which the immune system reacts to peptide antigens.The
critical interaction is that of peptide bound to major histocompatibility complex(pMHC) on the surface of antigen-presenting cells, which binds to T cell receptors(TCRs) on T lymphocytes. However,T cell activation requires that the affinity of this interaction be just right. If the TCR does not remain bound to pMHC long enough, activation is not completed. However, too high an affinity is not optimal because the system
must respond to exceedingly small amounts of pathogen-derived molecules. pMHC
molecules are thought to be amplified by serial interaction with multiple TCRs; thus,
weaker binding can be advantageous to signaling. Modeling of pMHC-TCR interactions
supports the concept of an ideal range of affinities for activation. Internalization of TCRs
appears to require recognition of TCRs that have interacted with pMHC but have sincedissociated, presumably producing biochemical changes in the TCR.Also, differences incross-reactivity of naïve and mature T cells may be mediated by changes in amounts of
intracellular signaling molecules that are available to interact with the TCR. — LBR

CREDITS: LYNCH & PATRICK NANO LETT. 10.1021/NL025694J (2002)

www.stke.org

Nature Immunol. 3, 926 (2002).

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