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many other interesting proper-
ties. Higher-order topological
insulating states, where regions
of interest are along edges and
at corners, have been difficult to
identify unambiguously. Peterson
et al. developed a theoretical
framework to help identify and
characterize these exotic states,
including a new topological
marker—the fractional charge
density—that can be used to
detect topological states of
matter when the spectroscopic
probe of gapless surface states
is not accessible. The agreement
between experimental work
and theory is encouraging for
applicability to other topological
platforms. —ISO
Science, this issue p. 1114
CANCER
How cancer cells adapt to stressBacteria adapt to harsh
conditions such as antibiotic
WEARABLE DEVICES
Improving ionic thermoelectricsUsing ions as charge carriers in
thermoelectric devices usually
requires using either thermal
diffusion or redox reactions at
two electrodes with different
temperatures. Han et al. lever-
aged both of these strategies
to develop a gelatin-based ionic
thermoelectric device that uses
alkali salts and an iron-based
redox couple to generate a large
thermopower. This device is
capable of generating useful
amounts of energy from body
heat. —BG
Science, this issue p. 1091
PLASTIC POLLUTION
Not just settlingWhat controls the distribution
of microplastics on the deep
seafloor? Kane et al. show that
the answer to that question is
more complicated than particles
simply settling from where they
are found on the sea surface
(see the Perspective by Mohrig).
Using data that they collected off
the coast of Corsica, the authors
show that thermohaline-driven
currents can control the distribu-
tion of microplastics by creating
hotspots of accumulation, analo-
gous to their role in causing
focused areas of seafloor sedi-
ment deposition. Such currents
also supply oxygen and nutrients
to deep-sea benthos, so deep-
sea biodiversity hotspots are also
likely to be microplastic hotspots.
—HJS
Science, this issue p. 1140;
see also p. 1055
CORONAVIRUS
Smothering fecal-oral coronavirus spreadDiarrhea is a common symptom
in patients with coronavirus
disease 2019 (COVID-19). Zang
et al. used organoid cultures of
cells from the epithelial lining of
human small and large intestine
as an in vitro model system with
which to study viral entry and
replication in enterocytes. Mature
enterocytes expressing the viral
receptor were susceptible to pro-
ductive infection, which was also
stimulated by the expression of a
protease involved in viral entry. A
subset of patients with COVID-19
shed high amounts of viral RNA
in feces, but experiments with
simulated human colonic fluid
suggested that any shed virus
would be rapidly inactivated
during transit through the colon.
—IRW
Sci. Immunol. 5, eabc3582 (2020).
TOPOLOGICAL OPTICS
Topological insulators in the spotlightIn addition to having an insulating
interior while at the same time
supporting conducting surface
states, topological insulators have
1076 5 JUNE 2020 • VOL 368 ISSUE 6495 sciencemag.org SCIENCE
RESEARCH
REPRODUCTIVE BIOLOGY
Local control of sperm maturation
Newly produced spermatozoa within the testis do not
have fertilizing ability but become fully functional when
they mature in the epididymis. The development of the
epididymis itself is dependent on testicular factors
arriving via luminal flow. Improper signaling between
the testis and epididymis is hypothesized to result in male
infertility. Kiyozumi et al. identified NELL2 as a testicular
luminal protein that binds to its receptor, ROS1, on the luminal
epididymis surface and induces epididymal differentiation
(see the Perspective by Lord and Oatley). In turn, differentiated
epididymis secretes a fertility-essential protease, ovochy-
mase-2, to make spermatozoa fully mature and functional.
Thus, testis-epididymis interorgan communication by this
“lumicrine” regulation ensures mammalian reproduction. —BAP
Science, this issue p. 1132; see also p. 1053
CR
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KIY
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I N SC IENCE J O U R NA L SEdited by Michael Funk
Fluorescence microscopy image revealing localization of the protease ovochymase-2
(purple) within the caput epididimus, which is part of the male reproductive tract in mammals
Published by AAAS
DEVELOPMENT
Making cartilage throughout lifeThe skeletons of newborn
mammals are soft and pliable
because they are composed
primarily of cartilage. During
growth to adulthood, most
cartilage is replaced by bone.
The remaining cartilage, such
as that found in the joints,
does not readily regenerate, so
joints deteriorate with age. By
contrast, elasmobranch fish
make cartilage throughout their
5 JUNE 2020 • VOL 368 ISSUE 6495 1077SCIENCE sciencemag.org
exposure by acquiring new
mutations, a process called
stress-induced mutagenesis.
Cipponi et al. investigated
whether similar programs of
mutagenesis play a role in the
response of cancer cells to
targeted therapies. Using in
vitro models of intense drug
selection and genome-wide
functional screens, the authors
found evidence for an analogous
process in cancer and showed
that it is regulated by the mam-
malian target of rapamycin
(mTOR) signaling pathway. This
pathway appears to mediate a
stress-related switch to error-
prone DNA repair, resulting in
the generation of mutations
that facilitate the emergence of
drug resistance. —PAK
Science, this issue p. 1127
ARCHAEOLOGY
Timing the rise of maize in MesoamericaMany lines of evidence suggest
that maize (Zea mays) became
a dietary staple across ancient
Mesoamerica. However, there
has been little direct evidence
of its consumption, and the
timing of how it came to domi-
nate the diet of the peoples of
the region is unknown. Using
stable isotopic evidence from
human skeletons excavated
from two rock shelter sites in
Belize, Kennett et al. show that
there is no clear evidence of
Edited by Caroline Ash
and Jesse SmithIN OTHER JOURNALS
maize consumption by the sites’
inhabitants before 4700 years
ago. However, isotopes from
more recent individuals show the
increasing importance of maize
in the diet, such that by 4000
years ago, maize had become a
persistent dietary staple. —MSA
Sci. Adv. 10.1126/sciadv.aba3245
(2020).
ANALYTICAL CHEMISTRY
Perfluorocarbons’ path into soilsCovering carbon chains with
fluorines has produced a variety
of useful nonstick coatings.
However, growing concern
about the toxicity and extraordi-
nary environmental persistence
of the underlying compounds is
spurring a search for alterna-
tives. The precise structure
of these next-generation
alternatives often remains a
trade secret. Washington et al.
sampled soils in New Jersey and
then used mass spectrometry
to assign plausible structures—
incorporating chlorine and ether
segments into the CF2 chain—to
compounds that appear to have
emanated from their manu-
facture (see the Policy Forum
by Gold and Wagner). The data
can inform in-depth studies of
these compounds’ environmen-
tal transport and persistence.
—JSY
Science, this issue p. 1103;
see also p. 1066
Maize, a global staple crop seen here growing in a field in El Salvador, rose to
dominate diets in Mesoamerica by 4000 years before present.PH
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MATERIALS SCIENCE
Better food preservation
Fresh fruits and vegetables are a key part of a healthy diet
but there can be considerable waste caused by spoilage
after harvest. Shelf life can be extended by preventing
microbial growth, dehydration, or storage at higher tem-
peratures, but adding a wax coating, creating a reduced
oxygen environment, or using refrigeration can be expensive
and/or time consuming and may alter the taste of the food.
Jung et al. developed an egg-sourced albumin coating rein-
forced with nanocrystalline cellulose that can be made from
waste materials. When coated onto banana, avocado, papaya,
and strawberry, shelf life was extended by a week, with reduced
external browning and internal ripening. The coatings are safe
to ingest but are also easily removed through washing. —MSL
Adv. Mater. 10.1002/adma.201908291 (2020).
Postharvest spoilage of fresh fruits and vegetables is reduced by a safe
and easily removed coating made with egg albumin.
Published by AAAS
5 JUNE 2020 • VOL 368 ISSUE 6495 1078-BSCIENCE sciencemag.org
CORONAVIRUS
Applications of antibody testingThere has been a strong focus
on testing to determine whether
an individual has an active severe
acute respiratory syndrome–
coronavirus 2 (SARS-CoV-2)
infection, but how do we find out
if someone has been infected
in the past? In a Perspective,
Krammer and Simon discuss the
key applications of serological
tests to detect antibodies against
SARS-CoV-2. Serological testing
could answer key questions
about whether neutralizing
antibodies form, and if they
do, serological studies could
assess the duration of immune
protection. Such tests could
also identify recovered patients
with high amounts of antibody
who could donate blood serum
for therapeutic use. In addition,
population serosurveys could
inform mitigation practices,
which could be especially impor-
tant during subsequent predicted
waves of infection. However, it is
important to ensure that tests are
accurate and sufficiently reliable
first. —GKA
Science, this issue p. 1060
COMPUTER SCIENCE
From bottom to topThe doubling of the number of
transistors on a chip every 2
years, a seemly inevitable trend
that has been called Moore’s law,
has contributed immensely to
improvements in computer per-
formance. However, silicon-based
transistors cannot get much
smaller than they are today, and
other approaches should be
explored to keep performance
growing. Leiserson et al. review
recent examples and argue that
the most promising place to look
is at the top of the computing
stack, where improvements in
software, algorithms, and hard-
ware architecture can bring the
much-needed boost. —JS
Science, this issue p. 1079
PLASMID EVOLUTION
Agrobacteria virulence writ largePlasmids are widespread among
bacteria and are important
because they spread virulence
and antibiotic resistance traits,
among others. They are horizon-
tally transferred between strains
and species, so it is difficult to
work out their evolution and
epidemiology. Agrobacteria, a
diverse grouping of species that
infect plants, inject oncogenic
Ti and Ri plasmids, which
cause crown galls and hairy
root diseases, respectively. The
upside is that these plasmids
have become valuable biotech-
nological tools. Weisberg et al.
combed through an 80-year-old
collection of Agrobacterium
strains but found a surprisingly
low diversity of plasmids. It is
puzzling how limited the number
of plasmid lineages is despite
reported high levels of plasmid
recombination, but what is clear
is how plant production systems
have influenced plasmid spread
into various genomic backbones.
—CA
Science, this issue p. 1080
STRUCTURAL BIOLOGY
Architecture of DNA-organizing complexThe highly conserved mam-
malian CTC1-STN1-TEN1
(CST) complex is critical for
genome stability and telo-
mere maintenance. Lim et al.
solved the structure of the
human CST complex using
cryo–electron microscopy. CST
forms an unprecedented and
substantial decameric super-
complex triggered by telomeric
single-stranded binding. This
decameric form with single-
stranded DNA–binding capacity
of up to 10 telomeric repeats,
suggested the possibility of CST
organizing telomere overhangs
into compact and restrictive
structures in a manner similar to
the nucleosome’s organization
of double-stranded DNA. This
work provides a platform for
understanding the mechanisms
of various CST functions. —SYM
Science, this issue p. 1081
CHEMICAL PHYSICS
Watching electrons swarm ammoniaLiquid ammonia is unusual in
its capacity to host electrons in
stable solution, with vivid blue
and bronze colors signifying the
low- and high-concentration
regimes, respectively. Buttersack
et al. used photoelectron spec-
troscopy and accompanying
theoretical simulations to track
the precise energetic changes
that ensued as steadily rising
quantities of electrons were
introduced by dissolved lithium,
sodium, or potassium (see the
Perspective by Isborn). The
results point to a gradual transi-
tion from the dilute electrolyte
solution of paired dielectrons to
the more delocalized metallic
structure at the highest concen-
trations. —JSY
Science, this issue p. 1086;
see also p. 1056
ORGANIC CHEMISTRY
Hydrogenations that tolerate N–O bondsCatalysts that add hydrogen to
carbon-carbon, carbon-nitrogen,
and carbon-oxygen double bonds
are among the most widely used
in synthetic chemistry. They are
particularly adept at delivering
just one of two mirror-image
products. However, they may
also target adjacent bonds in
the compound that would be
better left intact. Mas-Roselló et
al. report that an iridium catalyst
paired with a strong acid can
hydrogenate C=N bonds without
disturbing a weak N–O bond
on the same nitrogen center.
The reactions proceed at room
temperature with high enantiose-
lectivity. —JSY
Science, this issue p. 1098
NEUROSCIENCE
Making blind retinas see againPhotoreceptor degenera-
tion is an important cause of
blindness. Nelidova et al. used
tunable, near-infrared sensors
to render diseased photorecep-
tors light sensitive again (see
the Perspective by Franke and
Vlasits). Gold nanorods capable
of detecting infrared light were
coupled with an antibody to tem-
perature-sensitive ion channels.
When the nanorods absorbed
light and converted it into heat,
the coupled ion channels were
gated by infrared light. In a
mouse model of retinal degen-
eration, these ion channels were
successfully targeted to cone
photoreceptors, and responses
to near infrared light could be
detected. In the primary visual
cortex, more cells responded
to near-infrared stimuli in mice
expressing these ion channels
than in controls. By changing the
length of the gold nanorods, the
system could be tuned to differ-
ent infrared wavelengths. —PRS
Science, this issue p. 1108;
see also p. 1057
PALEOECOLOGY
Mangroves under sea level riseThe rate of sea level rise has
doubled from 1.8 millimeters
per year over the 20th century
to ~3.4 millimeters per year
in recent years. Saintilan et al.
investigated the likely effects
of this increasing rate of rise on
coastal mangrove forest, a tropi-
cal ecosystem of key importance
for coastal protection (see the
Perspective by Lovelock). They
reviewed data on mangrove
accretion 10,000 to 7000 years
before present, when the rate
of sea level rise was even higher
than today as a result of glacial
ice melt. Their analysis sug-
gests an upper threshold of
7 millimeters per year as the
maximum rate of sea level rise
Edited by Michael FunkALSO IN SCIENCE JOURNALS
RESEARCH
Published by AAAS
1078-C 5 JUNE 2020 • VOL 368 ISSUE 6495 sciencemag.org SCIENCE
associated with mangrove verti-
cal development, beyond which
the ecosystem fails to keep up
with the change. Under pro-
jected rates of sea level rise, they
predict that a deficit between
accretion and sea level rise is
likely to commence in the next
30 years. —AMS
Science, this issue p. 1118;
see also p. 1050
IMMUNOLOGY
Innate immune cells rememberImmunological memory is a phe-
nomenon by which immune cells
can quickly recognize an antigen
that the host has previously
encountered. Certain cells of the
innate immune system exhibit
memory-like responses know
as trained immunity. Rapid,
antigen-specific secondary
(anamnestic) responses were
long thought to be the domain of
B and T cells. However, Dai et al.
report that monocytes and mac-
rophages can acquire memory
specific for particular major
histocompatibility complex I
antigens using paired A-type
immunoglobulin-like receptors
(PIR-As) (see the Perspective by
Dominguez-Andrés and Netea).
This pathway contributes to
recognition and rejection of
allograft-transplanted tis-
sue from a donor of the same
species. Genetic depletion or
blockade of PIR-As in mice
diminished the rejection of
kidney and heart allografts.
This work, which expands
immunological memory to
include myeloid cells, points to
targets that may improve organ
transplantation outcomes in the
future. —STS
Science, this issue p. 1122;
see also p. 1052
MOLECULAR BIOLOGY
DNA barcodes in small packagesUnder adverse environmental
conditions, some microorgan-
isms form spores that provide
robust protection for genetic
material. Qian et al. developed a
system in which DNA barcodes
are encapsulated inside non-
germinating microbial spores
and can be dispersed on objects
or in the environment (see the
Perspective by Nivala). These
barcoded spores provide a
durable, specific marker that can
be read out quickly with simple
equipment. When applied to soil,
the spores can be transferred
to and from objects around
them, enabling tracking at
meter-scale resolution. On plant
leaves, the spores are not readily
transferred, and the authors
demonstrate a potential use for
tracking agricultural products.
—MAF
Science, this issue p. 1135;
see also p. 1058
GENE EDITING
Enforced editingVarious autoimmune diseases
could potentially be treated
with regulatory T cells (Tregs
),
but there are many hurdles
between this idea and clini-
cal execution. Honaker et al.
devised a gene-editing strategy
to enforce the expression of
FOXP3, the master Treg
tran-
scription factor, in CD4+ T cells
isolated from human peripheral
blood, thereby overcoming the
limitations of Treg
isolation and
expansion. The resulting stable
FOXP3 expression enabled a
suppressive phenotype in vitro,
and the edited cells were also
functional in both a xenogeneic
graft-versus-host disease model
and an experimental autoim-
mune encephalitis model. This
approach has the potential to
rapidly translate to clinical use.
—LP
Sci. Transl. Med. 12, eaay6422 (2020).
PHARMACOLOGY
More targeted endothelial protectionThe bioactive lipid S1P exerts
effects in diverse tissues.
Unbiased agonists of the S1P
receptor S1P1 trigger a reduced
lymphocyte count, or lympho-
penia, a useful feature when
treating autoimmune diseases
but an undesirable side effect
when activating S1P1 in other cell
types. Poirier et al. identified a
G protein–biased S1P1 agonist,
SAR247799, which maintained
endothelial function and reduced
tissue damage caused by
ischemia-reperfusion injury in
two different animal models. The
characteristics of SAR247799
show that it is possible to
target S1P1 in the endothelium
without compromising immune
responses. —WW
Sci. Signal. 12, eaax8050 (2020).
RESEARCH
Published by AAAS
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