38 3 JANUARY 2020 • VOL 367 ISSUE 6473 sciencemag.org SCIENCE
The interaction of checkpoint
pathways might allow opportuni-
ties to improve therapy. —PNK
Immunity 51 , 1059 (2019).
NEUROSCIENCE
Filling a blank canvas
Natural scenes can be decoded in
the brain in the early visual cortex.
Decoding is a product of planned
output (feedforward) corrected
by experience (feedback). Morgan
et al. occluded one quadrant of
the visual field of human partici-
pants and then presented them
with images of landscape scenes.
Responses in the visual cortex
(areas V1 and V2) were measured
for each person by functional
magnetic resonance imaging.
Even in the occluded region,
information about the scene was
being decoded. To access what
the brain had modeled for the
occluded region, participants
were asked to complete the image
by line drawings on an electronic
drawing tablet. The drawings were
shown to all participants, who
scored how well the “averaged”
drawing for each scene matched
the complete image. Mental
models at the first visual cortical
stage were predicted by the line
drawings. So, faced with a blank
canvas, an artist may be using
cortical feedback processing until
the lines and edges converge on
her mental model of a scene, thus
providing a window into her visual
cortex. —PRS
J. Neurosci. 39 , 9410 (2019).CELL BIOLOGY
Kill, but don’t be killed
Cytotoxic T lymphocytes (CTLs)
recognize and destroy infected
or malignant cells. CTLs secrete
the pore-forming protein per-
forin into the immune synapse,
where perforin disrupts the
target cell plasma membrane
and initiates cell death pathways.
Paradoxically, the secreted
perforin only damages the
target cell, leaving the producer
lymphocytes unscathed and
able to attack another target cell.
What protects the lymphocyte
is unclear. Using a variety of
approaches, Rudd-Schmidt et
al. found that two distinct but
coordinated mechanisms were
deployed by CTLs to protect
themselves. Both mechanisms
depended on the dynamic regu-
lation of plasma membrane lipid
composition and topology. High
membrane lipid order made
the CTL presynaptic membrane
refractory to perforin binding.
Furthermore, phosphatidyl-
serine, exposed on the killer cell
membrane, appeared to bindand inactivate perforin. —SMH
Nat. Commun. 10 , 5396 (2019).MICROBIOTA
Postantibiotic recovery
Antibiotic consumption by
humans is ubiquitous. Although
they are lifesaving and valuable
medicines, antibiotics can harm
resident mutualistic micro-
organisms in unpredictable ways
leading to physiological damage.
Ng et al. systematically explored
the long-term effects of antibi-
otic treatment on transplanted
human microbiota in mice. The
alpha-diversity of Bacteroides
spp. suffered mass extinction
by streptomycin within hours of
treatment, whereas Firmicutes
were more resilient. Such taxa-
specific selection depended on
the antibiotic used, influenced
the recovered community com-
position, and affected resilience
to subsequent treatments.
Diet was an important variable:
Without microbiota-accessible
fiber in the diet, mucus graz-
ers predominated, which may
facilitate the activity of patho-
gens, such as Acinetobacter
muciniphila. Recolonization from
untreated cage mates was also
vital for healthy reestablishment
of the microbiota, especially
of Bacteroidetes. It is possiblethat selective transplantation of
extinct taxa could aid a healthy
microbiota to recover after anti-
biotics exposure. —CA
Cell Host Microbe 26 , 650 (2019).PHYSICS
Tailoring electronic
properties
The layered material a-RuCl 3
has piqued the interest of physi-
cists as a potential platform for
the so-called Kitaev model—a
type of quantum spin liquid
that hosts exotic excitations.
However, in addition to the
magnetic interactions of the
Kitaev model, a-RuCl 3 also hosts
non-Kitaev interactions. Biswas
et al. investigated theoretically
whether a heterostructure
consisting of a a-RuCl 3 mono-
layer on top of graphene would
be a better approximation of
the Kitaev model. Using ab initio
calculations, the researchers
found that the a-RuCl 3 layer
would experience strain and
become doped by graphene
electrons. The strain would
make the Kitaev interactions
more dominant, and the doping
may provide a route towards
p-wave superconductivity in this
system. —JS
Phys. Rev. Lett. 123 , 237201 (2019).METALS IN BIOLOGYCopper on the half shell
O
ysters, like many marine mollusks, have
a complex life cycle that requires changes
in their body and biochemistry. Weng et al.
examined how the abundance and distribu-
tion of copper, a trace element essential for
metabolism, changes in larval and juvenile oysters
as they develop. Using a combination of imag-
ing techniques, they see copper accumulation in
certain organs during developmental transitions,
especially in the cells’ mitochondria. Both cell
proliferation and programmed cell death involve
biochemical processes linked to mitochondrial
copper concentrations. Understanding metal
ion distributions may offer insights valuable for
conservation and cultivation. —MAF
Environ. Sci. Technol. 53 , 14724 (2019).Oysters have a particularly critical need for the trace element
copper during their late pelagic larval stage (pictured).PHOTO: STEPHANIE ALEXANDER, UNIVERSITY OF MARYLAND CENTER FOR ENVIRONMENTAL SCIENCE HORN POINT OYSTER HATCHERYRESEARCH | IN OTHER JOURNALS
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