836 12 NOVEMBER 2021 • VOL 374 ISSUE 6569 science.org SCIENCE
PHOTOS: (LEFT TO RIGHT STEVE GSCHMEISSNER/SCIENCE SOURCE; ZUMA PRESS, INC./ALAMY STOCK PHOTORESEARCH | IN SCIENCE JOURNALS
to carbon atoms. The s-hole
gives rise to the halogen-bonding
mechanism, which is well known
in supramolecular chemistry
despite its existence being con-
firmed only indirectly. Mallada et
al. developed Kelvin probe force
microscopy with a specifically
functionalized tip and report
direct real-space visualization of
the s-hole, revealing its strong
anisotropic charge distribution.
The authors show that this tech-
nique, which relies entirely on
electrostatic interactions, may
be a powerful tool with which to
study anisotropic atomic charge
distributions. —YS
Science, abk1479, this issue p. 863
DENDRITIC CELLS
Infected lungs call
for backup
Resident dendritic cells (DCs)
within the lung epithelium are
positioned to rapidly detect
invading pathogens and initiate
an adaptive immune response.
They can also be expanded
through recruitment of blood-
derived progenitors. In a mouse
model of influenza virus infec-
tion, Cabeza-Cabrerizo et al.
showed that expression of the
chemokine receptor CCR2 is
required for recruitment of DC
progenitors (pre-DCs) to the
lungs and subsequent position-
ing at foci of infection. Using
mice with conditional deletion
of CCR2 in the DC lineage, they
MACROECOLOGY
Biotic interactions
limit range edges
Species ranges are strongly
influenced by climate, but spe-
cies interactions can also limit
ranges and constrain range
shifts with climate change.
Paquette and Hargreaves used
a meta-analysis of 338 stud-
ies of range limits from 654
taxa to test a long-standing
hypothesis that abiotic factors
are more important at cooler,
more stressful range edges
(high latitudes and elevations),
and biotic interactions limit
more biodiverse warm edges.
The authors found that spe-
cies interactions were more
important at warm than at cool
range edges. Climate affects
both warm and cool range
edges; however, incorporating
information about competition,
predation, and parasitism isespecially important for pre-
dicting changes in warm range
edges. —BEL
Ecol. Lett. 24 , 2427 (2021).PLANT SCIENCE
Light directs leaf shape
Coordinated patterns of cell
division followed by cell expan-
sion combine to define the
shape of a plant leaf. A wide,
flat leaf shape maximizes light
capture and gas exchange.
Phototropins in the leaf per-
ceive blue and ultraviolet light
direction and, through auxins,
locate signals for stems to
grow toward the light and for
leaves to flatten to maximize
light reception. Legris et al.
defined the signaling cascades
initiated by phototropins that
direct whether an Arabidopsis
leaf will be flat or curly. The
phototropins have their effect
rather late in leaf development,found that pre-DC recruitment
is necessary for effective
T cell responses and protec-
tion against reinfection. These
results demonstrate that expan-
sion of the homeostatic lung DC
network by circulating pre-DCs
is essential for immunity against
respiratory viruses. —CO
Sci. Immunol. 6 , eabi9331 (2021).PHYSICS
Dark matter declines
to reveal itself
Astrophysicists hold that our uni-
verse is dominated by mysterious
“dark” matter and energy that
puzzle outsiders and which, in
truth, are not yet well understood
even though their existence is
supported by many lines of evi-
dence. Several new fundamental
particles have been proposed as
candidates for dark matter, but
there are few claims of definitive
signals. An exception is the claim
by the DAMA collaboration of a
statistically significant annual
modulation in their event rate,
consistent with weakly interact-
ing massive particles, but this
result had seemed inconsistent
with other direct search experi-
ments. Adhikari et al. analyzed
data from a different collabora-
tion, COSINE-100, which appears
to exclude the DAMA result. Dark
matter thus remains elusive.
—WSW
S c i. Ad v. 10.1126/sciadv.abk2699
(2021).Dendritic cells, seen here in a colored scanning electron microscope image,
help detect and respond to pathogens in the lungs.
IN OTHER JOURNALS
Edited by Caroline Ash
and Jesse Smith