research - mit · far-red light–adapted enzymes that were chemically altered to shift their...

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1198 15 JUNE 2018 • VOL 360 ISSUE 6394 sciencemag.org SCIENCE

is consistent with adjacent layers

naturally having opposite mag-

netizations, which align parallel

to each other in high magnetic

fields. —JS

Science, this issue p. 1218, p. 1214

PHOTOSYNTHESIS

Lower-energy photons do the work, too Plants and cyanobacteria

use chlorophyll-rich photo-

system complexes to convert

light energy into chemical

energy. Some organisms

have developed adaptations

to take advantage of longer-

wavelength photons. Nürnberg

et al. studied photosystem

complexes from cyanobac-

teria grown in the presence

of far-red light. The authors

identified the primary donor

chlorophyll as one of a few

chlorophyll molecules in the

far-red light–adapted enzymes

that were chemically altered to

shift their absorption spec-

trum. Kinetic measurements

demonstrated that far-red light

is capable of directly driving

water oxidation, despite having

less energy than the red light

used by most photosynthetic

organisms. —MAF

Science, this issue p. 1210

CYTOMETRY

Seeing ghostsIn fluorescence-activated

cell sorting, characteristic

target features are labeled

with a specific fluorophore,

and cells displaying different

fluorophores are sorted. Ota

et al. describe a technique

called ghost cytometry that

allows cell sorting based on the

MACHINE LEARNING

A scene-internalizing computer program To train a computer to “rec-

ognize” elements of a scene

supplied by its visual sensors,

computer scientists typically use

millions of images painstakingly

labeled by humans. Eslami et

al. developed an artificial vision

system, dubbed the Generative

Query Network (GQN), that

has no need for such labeled

data. Instead, the GQN first

uses images taken from differ-

ent viewpoints and creates an

Edited by Stella HurtleyI N SC IENCE J O U R NA L S

RESEARCH

abstract description of the scene,

learning its essentials. Next, on

the basis of this representation,

the network predicts what the

scene would look like from a new,

arbitrary viewpoint. —JS


MAGNETISM

An intrinsic magnetic tunnel junction An electrical current running

through two stacked magnetic

layers is larger if their mag-

netizations point in the same

direction than if they point in

opposite directions. These so-

called magnetic tunnel junctions,

used in electronics, must be

carefully engineered. Two groups

now show that high magneto-

resistance intrinsically occurs in

samples of the layered mate-

rial CrI3 sandwiched between

graphite contacts. By varying

the number of layers in the

samples, Klein et al. and Song

et al. found that the electrical

current running perpendicular

to the layers was largest in high

magnetic fields and smallest

near zero field. This observation

HUMAN IMPACTS

Nocturnal refuge

As the human population grows, there are fewer

places for animals to live out their lives inde-

pendently of our influence. Given our mostly

diurnal tendencies, one domain that remains

less affected by humans is the night. Gaynor

et al. found that across the globe and across mam-

malian species—from deer to coyotes and from

tigers to wild boar—animals are becoming more

nocturnal (see the Perspective by Benítez-López).

Human activities of all kinds, including nonlethal

pastimes such as hiking, seem to drive animals to

make use of hours when we are not around. Such

changes may provide some relief, but they may also

have ecosystem-level consequences. —SNV

Science, this issue p. 1232; see also p. 1185

Human activities are driving many

animals, including coyotes (Canis latrans)

like this one, to become more nocturnal.

Tau binding to tubulin monomers Kellogg et al., p. 1242

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15 JUNE 2018 • VOL 360 ISSUE 6394 1199SCIENCE sciencemag.org

morphology of the cytoplasm,

labeled with a single-color

fluorophore. The motion of cells

relative to a patterned optical

structure provides spatial

information that is compressed

into temporal signals, which

are sequentially measured by

a single-pixel detector. Images

can be reconstructed from this

spatial and temporal informa-

tion, but this is computationally

costly. Instead, using machine

learning, cells are classified

directly from the compressed

signals, without reconstruct-

ing an image. The method

was able to separate morpho-

logically similar cell types in an

ultrahigh-speed fluorescence

imaging–activated cell sorter.

—VV


ANTHROPOLOGY

Mesoamerican turquoise locally sourcedScholars have long assumed

that Aztec and Mixtec tur-

quoise artifacts uncovered in

Mesoamerica were imported

from the American Southwest,

which is home to abundant

turquoise deposits. Thibodeau

et al. analyzed the lead and

strontium isotopic ratios in

38 Mesoamerican turquoise

mosaic tiles (tesserae) from the

Sacred Precinct of Tenochtitlan

and in five tesserae from Mixtec

turquoise mosaics. The isoto-

pic compositions of most of

the samples matched copper

Edited by Caroline Ash

and Jesse SmithIN OTHER JOURNALS

deposits and crustal rocks of

Mesoamerica, suggesting at least

one Mesoamerican region as the

source of this turquoise. —PJB

Sci. Adv. 10.1126/sciadv.aas9370

(2018).

NEUROSCIENCE

Disentangling specific memories Each memory is stored in a

distinct memory trace in the

brain, in a specific population of

neurons called engram cells. How

does the brain store and define

the identity of a specific memory

when two memories interact and

are encoded in a shared engram?

Abdou et al. used optogenetic

reactivation coupled with manipu-

lations of long-term potentiation

to analyze engrams that share

neurons in the lateral amygdala

(see the Perspective by Ramirez).

Synapse-specific plasticity

guaranteed the storage and the

identity of individual memories in

a shared engram. Moreover, syn-

aptic plasticity between specific

engram assemblies was neces-

sary and sufficient for memory

engram formation. —PRS

Science, this issue p. 1227;

see also p. 1182

INFECTIOUS DISEASE

Designer bugs as drugsThe endemic persistence and

outbreaks of Vibrio cholerae

indicate a need for new methods

of control. Mao et al. discovered

that lactic acid production by the

probiotic Lactococcus

lactis rendered the

infant mouse gut hostile

to V. cholerae and

engineered L. lactis to

detect breakthrough

infection. Hubbard et al.

extensively modified a

contemporary V. chol-

erae strain for a live oral

vaccine, which resulted

in an attenuated strain

that could protect infant

rabbits from V. cholerae

challenge within 24

hours of vaccine admin-

istration. —LP

Sci. Transl. Med. 10,

eaao2586, eaap8423 (2018).

Isotope analysis indicates a Central American

source for Aztec turquoise.

Part of the Compact Muon Solenoid at CERN’s Large Hadron Collider

PARTICLE PHYSICS

In the company of top quarks

The coupling of elementary particles to the Higgs boson

is correlated with their masses. For some particles, it

can be measured by observing the decay of the Higgs

into those particles. The top quark, however, is too heavy

for the Higgs to decay into. Therefore, Sirunyan et al.

from the Compact Muon Solenoid Collaboration at the Large

Hadron Collider (LHC) looked at the processes in which the

Higgs boson is produced in conjunction with the top quark

and its antiparticle. By combining the results from the runs at

different center-of-mass energies of proton-proton collisions

at the LHC, they found that such processes indeed occurred

and that the signal strength was consistent with the predic-

tions of the Standard Model of particle physics. —JS

Phys. Rev. Lett. 120, 231801 (2018).

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RESEARCH

sciencemag.org SCIENCE

ALSO IN SCIENCE JOURNALS

IMMUNOLOGY

Modeling memory differentiation in T cells The balance between effector

and central memory T cells

shifts toward the latter as the

number of T cells participating

in immune responses increases.

Polonsky et al. determined the

mechanisms by which T cell

quorum sensing affects memory

differentiation by using live-cell

imaging to track cell proliferation

and differentiation. They found

that the rate of memory CD4+

T cell differentiation is deter-

mined by cell number. This rate

substantially increases above

a threshold number of locally

interacting cells. Mathematical

modeling suggests that the num-

ber of initially seeded cells and

the number of cell divisions are

not critical. Instead, the instan-

taneous number of interacting

cells continuously modulates the

differentiation rate. This is partly

fueled by increased sensitivity

to the cytokines interleukin-2

(IL-2) and IL-6, independent of

any effects on cell proliferation.

—STS


CANCER

Chronic stress as a survival tactic Most patients with pancreatic

ductal adenocarcinoma (PDA)

develop liver metastases after

surgical removal of their primary

tumor. These metastases are

thought to potentially arise from

quiescent disseminated cancer

cells, likely present at the time of

surgery, which evade elimination

by the immune system. Pommier

et al. explored how these

quiescent cells survive by ana-

lyzing mouse models and tissue

samples from patients with PDA.

They found that disseminated

cancer cells do not express a cell

surface molecule that triggers

killing by T cells. This pheno-

typic feature is linked to their

inability to resolve endoplasmic

reticulum stress. When this

stress is resolved, the dissemi-

nated cells begin proliferating

and form metastases. —PAK


NANOTECHNOLOGY

Reconsidering resonator sensing Changes in the frequency

of a nanoscale mechanical

resonator can be used for many

sensing applications, provided

that there is an adequate signal-

to-noise ratio. Normally, this

ratio is improved by creating

resonators with higher quality

factors that “ring” for longer

times. Taking a cue from the

approaches used in atomic

force microscopy, Roy et al.

show that if the thermomechan-

ical noise of the resonator is

well defined, the signal-to-noise

ratio of the frequency shift can

improve by lowering the quality

factor. They used this approach

to demonstrate temperature

sensing with a double-clamped

silicon beam resonator, which

performed better at ambient

pressures than in a vacuum.

—PDS


PLANT SCIENCE

How to make bioactive alkaloidsVinblastine and vincristine are

important, expensive anticancer

agents that are produced by

dimerization of the plant-derived

alkaloids catharanthine and

vindoline. The enzymes that

transform tabersonine into

vindoline are known; however,

the mechanism by which the

scaffolds of catharanthine and

tabersonine are generated has

been a mystery. Caputi et al. now

describe the biosynthetic genes

and corresponding enzymes

responsible. This resolves a

long-standing question of how

plant alkaloid scaffolds are

synthesized, which is important

not only for vinblastine and

vincristine biosynthesis, but

also for understanding the many

other biologically active alkaloids

found throughout nature. —PJH


NEUROSCIENCE

The mechanisms of fear attenuation Surprisingly little is known

about how remote fearful mem-

ories are stored and attenuated.

Khalaf et al. used independent

fear memory attenuation para-

digms, engram-based tagging

techniques, and chemogenetic

tools to alter neuronal activ-

ity (see the Perspective by

Frankland and Josselyn). They

found that a discrete subset of

neurons within an ensemble

is engaged during recall after

memory attenuation, which

correlated with fear reduction.

Memory updating and extinc-

tion mechanisms thus likely

coexist to make this happen.

These findings support the

notion that effective memory

attenuation is mediated by a

rewriting of the original memory

trace of fear toward one of

safety. —PRS


see also p. 1186

STRUCTURAL BIOLOGY

Tackling microtubule-tau interactions Alzheimer’s disease is a major

cause of death in the elderly.

Disease progression is associ-

ated with the accumulation

of neurofibrillary tangles

composed of tau, a protein

important for neuronal devel-

opment and function. Tangle

formation is preceded by phos-

phorylation events that cause

tau to dissociate from its native

binding partner, microtubules.

Microtubule-tau interactions

have been mysterious. Kellogg

et al. used cryo–electron

microscopy and molecular

modeling to show how tau

interacts with the outer surface

of the microtubule, stapling

together tubulin subunits and

thus stabilizing the polymer. A

key tau amino acid within the

tightly bound segment between

tubulin subunits corresponds

to a clinically relevant site of

tau phosphorylation, explain-

ing the competition between

microtubule interaction and tau

aggregation. —SMH


NEUROSCIENCE

Shifts in brain regions with brain size Brain size among normal

humans varies as much as

twofold. Reardon et al. surveyed

the cortical and subcortical

structure of more than 3000

human brains by noninvasive

imaging (see the Perspective

by Van Essen). They found that

the scaling of different regions

across the range of brain sizes

is not consistent: Some brain

regions are metabolically costly

and are favored in larger brains.

This shifts the balance between

associative and sensorimotor

brain systems in a brain size–

dependent way. —PJH


see also p. 1184

OCEANS

Environmental DNA tracks rare speciesMarine animals are often elusive,

making it difficult to establish

their presence in a region or to

estimate population sizes. Many

of these animals are also rare,

making them even more difficult

to study. In a Perspective, Pikitch

highlights the advantages of

environmental DNA studies for

detecting rare marine animals,

particularly to aid conservation

efforts. The method is noninva-

sive and highly sensitive, allowing

detection of the recent presence

of animals such as killer whales.

Edited by Stella Hurtley

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However, challenges remain, par-

ticularly for estimating population

sizes, where the approach should

prove useful in combination with

more established methods. —JFU


IMMUNOLOGY

Letting thymocytes goDuring the process of T cell

development, thymocytes

must travel from the

cortex of the thymus to the

medulla, where potentially

autoreactive cells are removed

by negative selection. Duke-

Cohan et al. found that mouse

thymocytes lacking the guano-

sine triphosphatase–activating

protein Tagap failed to detach

from the cortex. Given that in

humans, single-nucleotide poly-

morphisms in the gene encoding

TAGAP are associated with

autoimmune disorders, the data

suggest that this protein facili-

tates the trafficking required for

the efficient negative selection of

autoreactive cells. —JFF

Sci. Signal. 11, eaan8799 (2018).

HIV

Spontaneous HIV controllersA small number of HIV-infected

individuals (<1%) can spontane-

ously control HIV in the absence

of antiretroviral therapy. Because

CD4+ and CD8+ T cell responses

are thought to contribute to

protection, HIV-responsive T cell

receptors (TCRs) from these

individuals are of considerable

interest. Galperin et al. examined

how three class II–restricted

TCRs observed in spontane-

ous controllers are capable of

binding a Gag peptide in the

context of multiple HLA-DR mol-

ecules (HLA, human leukocyte

antigen). The authors solved the

structures of several TCR–

peptide–HLA-DR complexes.

The findings suggest that the

ability of these TCRs to recognize

the Gag peptide in the context

of multiple HLA-DR allomorphs

is shaped by extensive contacts

between the TCRs and the

peptide itself. —AB

Sci. Immunol. 3, eaat0687 (2018).

15 JUNE 2018 • VOL 360 ISSUE 6394 1200-C

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Designer bugs as drugsLindsey Pujanandez

DOI: 10.1126/science.360.6394.1198-h (6394), 1198-1199.360Science

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