research - science · 2020. 7. 16. · science, this issue p. 1247 insect locomotion robot on a...

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12 JUNE 2020 • VOL 368 ISSUE 6496 1201SCIENCE sciencemag.org

MESOSCOPIC PHYSICS

Coherent electronic wavesThe wave nature of conduct-

ing electrons in solids can be

revealed through interference

effects. In layered materials,

these effects are most often

seen in in-plane transport. By

contrast, Putzke et al. studied

electronic transport perpen-

dicular to the conductive layers

in the ultraclean delafossites

PdCoO2 and PtCoO

2. When

an in-plane magnetic field

was applied, the electrical

resistance exhibited periodic

oscillations as a function of

field magnitude. The findings

can be explained through

a model that requires that

the electronic waves remain

coherent over macroscopic

distances. —JS

Science, this issue p. 1234

CELL CYCLE

How cells monitor mitogen availabilityClassical experiments indicated

that cells sense the mitogens or

growth factors that control cell

division within a limited window

during the cell cycle. Min et al.

reexamined this issue with high-

throughput live-cell imaging and

temporally controlled perturba-

tions to more closely monitor

dynamic signal processing.

Human epithelial cells in culture

integrated the mitogenic signals

sensed throughout the cell

cycle. One important factor

was the control of transla-

tion rates, which influenced

the amount of cyclin D, thus

regulating proliferation. The

results may also help to explain

how cells maintain a uniform

size. —LBR


PROTEIN FOLDING

Shedding light on disordered proteinsDisordered proteins often fold

as they bind to a partner protein.

There could be many different

molecular trajectories between

the unbound proteins and the

bound complex. Most methods

to measure transition paths

rely on monitoring a single

distance, making it difficult to

resolve complex pathways. Kim

and Chung used fast three-

color single-molecule Foster

resonance energy transfer

(FRET) to simultaneously probe

distance changes between the

two ends of an unfolded protein

and between each end and a

probe on the partner protein.

They show that binding can be

initiated by diverse conforma-

tions and that the molecules

are held together by non-native

interactions as the disordered

protein folds. This allows the

association to be diffusion lim-

ited because most collisions lead

to binding. —VV


NANOPHOTONICS

Light under compressionThe ability to confine light to

volumes much smaller than

the wavelength produces high

electromagnetic fields that can

then be exploited in chemi-

cal and biological sensing and

detection applications. Using

silver nanocubes placed on a

graphene surface, Epstein et

al. developed a single, nano-

meter-scale acoustic graphene

plasmon cavity device that

can confine mid-infrared and

terahertz radiation with mode

volume confinement factors

of 5 × 1010. With the response

RESEARCH

OCEANOGRAPHY

Coral reef islands adjust to rising sea

Gravel-covered islands that develop naturally atop coral reefs have

long provided opportunities for human habitation in the tropics,

but there is widespread concern that such communities may be at

risk because of sea level rise. However, Masselink et al. suggest that

these islands may be able to adjust dynamically to changes in sea level.

Numerical modeling of sediment transport on these islands during limited to

moderate sea level rise indicated that foundering beneath the waves is not inev-

itable. Instead, sediment redistribution may simply change island geography

and topography. Although the authors note that this process would be societally

problematic, it may at least preserve the short-term habitability of coral reef

islands. —KVH Sci. Adv. 10.1126/sciadv.aay3656 (2020).

Funafuti atoll, the capital of the Pacific island nation Tuvalu, is threatened by rising sea level,

which may also change patterns of sediment deposition.

I N SC IENCE J O U R NA L S

Edited by Michael Funk

Published by AAAS

SIGNALING

Controlling blood flow in the liverHigh blood pressure in the

liver created by fibrosis causes

serious clinical illness. Blood

pressure is regulated by nitric

oxide, but this is depleted if

hepatic sinusoidal endothelial

cells are damaged. The scaffold

protein b-arrestin 2 (b-Arr2)

regulates the activity of endo-

thelial cell nitric oxide synthase

(eNOS) in rodent liver. Liu et al.

found that in rodents, b-Arr2,

which serves several functions

in G protein–coupled receptor

signaling, helps to control eNOS

at endothelin receptors. b-Arr2

promoted the association of

another protein called GIT1 with

eNOS, which activates eNOS.

Apparently, b-Arr2 and other

signaling components form a

signalsome near the endothe-

lin receptors, which regulates

eNOS function. Disruption

of this signaling contributes

to the liver injury and portal

hypertension that cause lethal

liver disease in humans. —LBR

Proc. Natl. Acad. Sci. U.S.A. 117, 11483

(2020).

MIGRATION

Should I stay or should I go?The global upheaval of seasonal

bird migration is an astonishing

phenomenon. The European

blackcap is a species of small

songbird that shows great varia-

tion in wanderlust. Delmore et

al. collected DNA-sequencing

data from blackcaps across

their breeding range to deter-

mine the genetic basis for

variations in migratory behavior.

The impulse to migrate and the

distance and direction of travel

are encoded in small genomic

regions. Polymorphisms were

found in genes for transcription

factors such as Clock, Npas2,

and Bma1, which are associated

with circadian rhythm. A few

genes linked to traits as varied

1202 12 JUNE 2020 • VOL 368 ISSUE 6496 sciencemag.org SCIENCE

RESEARCH | IN SCIENCE JOURNALS

Edited by Caroline Ash

and Jesse SmithIN OTHER JOURNALS

being dependent on the size of

the nanocube and electrically

tunable, the results demonstrate

a powerful platform with which

to develop sensors in what has

been a challenging wavelength

regime where molecular finger-

prints reside. —ISO


MOLECULAR MACHINES

Ten rings on one axleRotaxanes consist of molecu-

lar rings threaded on a central

axle. Most approaches to their

synthesis have focused on

introducing a single ring per axle.

Qiu et al. now report a system-

atic approach to threading up to

10 adjacent rings consecutively.

The axle’s end groups were con-

structed to attract free-floating

rings when reduced and then to

push those rings toward the cen-

ter upon oxidation. Products of

each successive reduction-oxi-

dation cycle were characterized

by nuclear magnetic resonance

spectroscopy and mass spec-

trometry. —JSY


INSECT LOCOMOTION

Robot on a wireStudying the free flight of

insects using artificial systems

such as tethered flight or flight

in confined environments can

cause the insect to fly in an

unnatural way. Pannequin et al.

report a cable robot consist-

ing of an open cage mounted

with cameras, which they call

“lab-on-cables.” The cable robot

moves automatically with the

flying insect by using reactive

controllers to track the insect’s

flight in natural conditions with

limited disturbance. Using this

system, the researchers were

able to study Agrotis ipsilon

moths flying freely at speeds

of up to 3 meters per second.

—MML

Sci. Robot. 5, eabb2890 (2020).

ICE SHEETS

Taking stock of our lossesEarth’s ice sheets are melting

and sea levels are rising, so it

behooves us to understand bet-

ter which climate processes are

responsible for how much of the

mass loss. Smith et al. estimated

grounded and floating ice mass

change for the Greenland and

Antarctic ice sheets from 2003

to 2019 using satellite laser

altimetry data from NASA’s

ICESat and ICESat-2 satellites.

They show how changing ice

flow, melting, and precipitation

affect different regions of ice and

estimate that grounded-ice loss

averaged close to 320 gigatons

per year over that period and

contributed 14 millimeters to sea

level rise. —HJS


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A cable-driven robot

capable of autonomous

tracking of free-

flying insects in three

dimensions

GENETICS

Big cat genomics

The lion may be the king of beasts, but over the past

~14,000 years, their range has decreased substan-

tially and many current populations are in decline.

To understand the historical population genomics of

lions, de Manuel et al. sequenced cave lion remains

from ~30,000 years ago, several historic specimens

from extinct populations over the past ~500 years, and

samples from extant populations. From this, they were

able to reconstruct relationships among lion populations

over time. No evidence of gene flow between cave lions

and recent lion populations was detected. Modern lion

groups that diverged into northern and southern lineages

show evidence of admixture, especially in extant central

African populations. These data could be valuable not

only because they indicate the relationships between

modern and extinct populations but also because they

reveal a historical level of inbreeding that could be rel-

evant to conservation efforts. —LMZ

Proc. Natl. Acad. Sci. U.S.A. 117, 10927 (2020).

Published by AAAS

1203-B 12 JUNE 2020 • VOL 368 ISSUE 6496 sciencemag.org SCIENCE

RESEARCH

NEUROSCIENCE

Receptors moving in and out of the synapseThe number of neurotransmit-

ter receptors and their spatial

organization on the postsynaptic

site is a central determinant of

synaptic efficacy. Sophisticated

techniques to visualize and

track the movement of single

molecules have provided us

with profound new insights into

these dynamics. We now know

that neurotransmitter receptors

undergo movements on different

scales. Groc and Choquet review

our present understanding of

the mechanisms that regulate

glutamate receptor localization

and clustering. Receptor move-

ments are fundamental to basic

synaptic function and participate

in many forms of synaptic plas-

ticity. —PRS


CORONAVIRUS

Repurposing existing vaccinesSince the 1950s, we have had

evidence that live attenuated

vaccines can induce protection

from infections that are not

included in the vaccine. This

has especially been the case

for the oral poliovirus vaccine

(OPV), which induces protection

against various other pathogens,

including influenza viruses.

In a Perspective, Chumakov

et al. discuss the evidence for the nonspecific protective

effects of live vaccines, includ-

ing Bacillus Calmette-Guérin

(BCG) for tuberculosis and OPV.

These nonspecific effects might

be efficacious in protecting

against severe acute respira-

tory syndrome coronavirus 2

(SARS-CoV-2). Trials using BCG

to protect against SARS-CoV-2

infection are under way, and the

authors recommend that OPV

should also be tested for this use

because it has a strong safety

profile and production could be

scaled up quickly. If successful,

this strategy could protect the

most vulnerable individuals from

SARS-CoV-2 infection. —GKA


CELL BIOLOGY

Actin cortex controls cell migrationCell migration is mainly

controlled by local actin polym-

erization–driven membrane

protrusion. However, a second

structural mechanism might also

regulate membrane protrusions

and directed migration: changes

in the density of the attachment

between the plasma membrane

and the underlying F-actin

cortex, a parameter related to

membrane tension. Many types

of attachment and signaling

mechanisms are known to

alter the density of membrane-

proximal cortical actin. Bisaria

et al. designed a membrane-

proximal F-actin (MPA) reporter

that could directly measure local

changes in the density of MPA in

living cells. Levels of MPA were

surprisingly low toward the front

of migrating cells despite an

opposing high overall concentra-

tion of F-actin in the same front

region. The researchers propose

that MPA density can integrate

different signaling processes to

direct local membrane protru-

sions and stabilize cell polarity

during cell migration. —SMH


STRUCTURAL BIOLOGY

Drug inhibition of glycosyltransferasesMycobacteria, including the

species that causes tuberculo-

sis (TB), synthesize a complex

cell wall that helps to support

and protect the bacterial cells.

The major components of

the cell wall include complex

heteropolysaccharides that

are synthesized in the peri-

plasmic space. Zhang et al.

determined the cryo–electron

microscopy structures of two

transmembrane glycosyltrans-

ferase enzyme complexes that

use a lipid-anchored sugar donor

to append arabinose units to

the cell wall polysaccharides.

They also captured the anti-TB

drug ethambutol bound within

these complexes and observed

that it binds in a site overlap-

ping both donor and acceptor

sugars. Mapping of resistance

mutants provides a structural

understanding of how resis-

tance emerges while preserving

function of the enzyme and may

help to guide the development

of next-generation anti-TB drugs

that target these enzymes.

—MAF


GEOPHYSICS

Sequencing for seismic structuresStructures illuminated by seis-

mic waves at the core-mantle

boundary of the Earth are tra-

ditionally found by focusing on

a specific target area. Kim et al.

used an unsupervised manifold

learning algorithm called “the

Sequencer” to automatically

detect anomalies in seismic

data (see the Perspective by

Miller). Using this technique,

they uncovered structures

at the core-mantle boundary

across the entire Pacific region

all at once. They found many

structures previously identified,

but also a new, ultra-low-velocity

zone beneath the Marquesas

Islands. —BG

Science, this issue p. 1223;

see also p. 1183

ELECTROCHEMISTRY

Charging into epoxidesEthylene oxide is a strained,

reactive molecule produced

on a vast scale as a plastics

precursor. The current method

of synthesis involves the direct

reaction of ethylene and oxygen

at high temperature, but the

original protocol relied on the

reduction of chlorine to produce

a chlorohydrin intermediate.

Leow et al. report a room tem-

perature method that returns

to the chlorine route but uses

electrochemistry to generate it

catalytically from chloride (see

the Perspective by Barton). This

efficient process uses water in

place of oxygen and can be inte-

grated with the electrochemical

generation of ethylene from

carbon dioxide. Propylene oxide

can be produced using the same

method. —JSY


see also p. 1181

PLASTIC POLLUTION

Here, there, and everywhereNo place is safe from plastic

pollution. Brahney et al. show

that even the most isolated

areas in the United States—

national parks and national

wilderness areas—accumulate

microplastic particles after they

are transported there by wind

and rain (see the Perspective by

Rochman and Hoellein). They

estimate that more than 1000

metric tons per year fall within

south and central western U.S.

protected areas. Most of these

plastic particles are synthetic

microfibers used for making

clothing. These findings should

underline the importance of

reducing pollution from such

materials. —HJS


see also p. 1184

ECOLOGICAL ECONOMICS

The benefits of ecosystem restorationHuman activities have fun-

damentally altered many

ecosystems. Recent successful

restoration efforts have led to

healthier ecosystems, but this

has led to a disruption in econo-

mies dependent on the altered

state of the system. One of the

best-known trophic cascades is

the sea otter–kelp forest system,

Edited by Michael FunkALSO IN SCIENCE JOURNALS

Published by AAAS

12 JUNE 2020 • VOL 368 ISSUE 6496 1203-CSCIENCE sciencemag.org

RESEARCH

wherein recovery of once

extirpated sea otters is bring-

ing back biodiverse and healthy

kelp forests but reducing the

abundance of harvested shell-

fish. Gregr et al. looked at the

costs and benefits of this shift

and found that for key trade-offs,

the value of kelp forest–associ-

ated features such as tourism,

fin fish fisheries, and carbon

capture outweighed the losses to

economies (see the Perspective

by Estes and Carswell). Thus,

ecosystem recovery can benefit

both ecosystems and econo-

mies. — SNV


see also p. 1178

SEXUAL DIMORPHISM

Canaries changing colorsMany animals are sexually

dimorphic, with different phe-

notypes in males and females.

To identify the genetic basis

of sexual differences in bird

coloration, Gazda et al. investi-

gated red coloration in mosaic

canaries and related species

(see the Perspective by Chen).

Using a combination of genetic

crosses, genomic mapping, tran-

scriptomics, and comparative

analyses, the authors show that

trans-regulation of the carot-

enoid-processing gene BCO2

is involved in sexual dichroma-

tism. Although such variation in

coloration among the sexes is

common, particularly in birds,

there are few candidate genes

known to be involved. This study

helps to elucidate the molecular

mechanisms that underlie the

evolution of dichromatism and

may aid in uncovering sexually

selected traits. —LMZ


see also p. 1185

BIOTECHNOLOGY

Very fast CRISPR on demandNumerous efforts have been

made to improve the temporal

resolution of CRISPR-Cas9–

mediated DNA cleavage to

the hour time scale. Liu et

al. developed a Cas9 system

that achieved genome-editing

manipulation at the second time

scale (see the Perspective by

Medhi and Jasin). Part of the

guide RNA is chemically caged,

allowing the Cas9-guide RNA

complex to bind at a specific

genomic locus without cleav-

age until activation by light. This

fast CRISPR system achieves

genome editing at high temporal

resolution, enabling the study of

early molecular events of DNA

repair processes. This system

also has high spatial resolution

at short time scales, allowing

editing of one genomic allele

while leaving the other unper-

turbed. —SYM


see also p. 1180

CORONAVIRUS

An antibody defense against COVID-19One of the responses of the

immune system to invading

viruses is the production of

antibodies. Some of these are

neutralizing, meaning that they

prevent the virus from being

infectious, and can thus be

used to treat viral diseases. Wu

et al. isolated four neutralizing

antibodies from a convales-

cent coronavirus disease 2019

(COVID-19) patient. Two of the

antibodies, B38 and H4, blocked

the receptor binding domain

(RBD) of the viral spike protein

from binding to the cellular

receptor, angiotensin-converting

enzyme 2 (ACE2). The struc-

ture of the RBD bound to B38

shows that the B38-binding

site overlaps with the binding

site for ACE2. Although H4 also

blocks RBD binding to ACE2,

it binds at a different site, and

thus the two antibodies can

bind simultaneously. This pair of

antibodies could potentially be

used together in clinical applica-

tions. —VV


MUSCLE PHYSIOLOGY

Autism and musclesMutations in the gene SHANK3,

which encodes a postsynaptic

protein, are associated with

autism spectrum disorders

(ASDs) and Phelan-McDermid

syndrome (PMDS). Children with

ASD or PMDS present neurode-

velopmental abnormalities and

skeletal muscle hypotonia; how-

ever, the mechanisms mediating

the decreased muscle tone are

unclear. Lutz et al. used patient-

derived material and a mouse

model to show that SHANK3 is

expressed in muscle sarcomeres

and plays a role in the matu-

ration of the neuromuscular

junctions (NMJs). Muscle biop-

sies from patients with PMDS

showed alterations in NMJs and

sarcomeres. Similarly, Shank3

deficiency in mice resulted

in smaller NMJs, sarcomere

abnormalities, and hypotonia.

Muscular deficits in mice were

rescued with the troponin activa-

tor tirasemtiv, suggesting that

this drug might also be effective

for treating hypotonia in patients

with SHANK3 mutations. —MM

Sci. Transl. Med. 12, eaaz3267 (2020).

FIBROSIS

Leaky blood vessels to kidney fibrosisInjury can result in a cellular

transdifferentiation program

called the endothelial-to-mes-

enchymal transition (EndMT).

Lovisa et al. found that EndMT

in the kidney triggers fibrosis

(see the Focus by Balzer and

Susztak). EndMT in response

to kidney injury led to vascular

disruptions. The ensuing tissue

hypoxia caused a Myc-induced

metabolic switch to glycolysis

in tubular epithelial cells that

culminated in fibrosis and

compromised kidney function.

Blocking EndMT in endothelial

cells or inhibiting Myc or glycoly-

sis in epithelial cells prevented

kidney fibrosis and dysfunction

after injury. —WW

Sci. Signal. 13, eaaz2597, abb8834

(2020).

NEUROIMMUNOLOGY

Safeguarding the sense of smellGiven the proximity of the olfac-

tory bulb to the upper airways,

it is surprising that viruses

that infect the upper airways,

including influenza, rarely infect

the brain. In mice, intranasal

infection with vesicular stoma-

titis virus (VSV) does result in

infection of sensory neurons

in the olfactory bulb. Using

VSV that expresses a fluores-

cent reporter, Moseman et al.

examined the ability of VSV to

infect distinct cell types within

the olfactory bulb. Although

VSV infection was restricted to

neurons within the olfactory

bulb, they found that microglial

cells that were not infected by

VSV were key in priming T cell

responses that promoted viral

clearance. —AB

Sci. Immunol. 5, eabb1817 (2020).

Published by AAAS

research - science · 2020. 7. 16. · science, this issue p. 1247 insect locomotion robot on a...

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