486 1 MAY 2020 • VOL 368 ISSUE 6490 sciencemag.org SCIENCE
RESEARCH | IN OTHER JOURNALS
dependent splitting of Landau
levels. The authors interpreted
this splitting in terms of valley
polarization, suggesting that the
findings may contribute to the
control of the valley degree of
freedom in the emerging field of
valleytronics. —JS
Phys. Rev. Lett. 124 , 106802 (2020).
EPIDEMIOLOGY
SARS-CoV-2 in Iceland
Like so many countries, Iceland,
with its population of 364,000
inhabitants, has been stricken
by severe acute respiratory
syndrome coronavirus 2 (SARS-
CoV-2). From 13 January through
4 April 2020, 13.3% of 9199 per-
sons chosen for testing because
they had symptoms or had trav-
eled from places of high risk were
found to be positive. Voluntary
testing of 13,080 people from the
general population revealed that
0.8% were positive for SARS-
CoV-2. Using contact tracing,
Gudbjartsson et al. revealed
that the source of infection
shifted over time, from travel to
family contact. Viral sequencing
data confirmed how imported
viral strains spread to others in
Iceland. The data from late March
indicate a stable infection rate,
showing the effect of the social
distancing measures that Iceland
put in place. —PJH
N. Engl. J. Med. 10.1056/
NEJMoa2006100 (2020).NEUROSCIENCE
Circuit promotes
overeating
Compulsive eating can be
induced in rodents by stimula-
tion of g-aminobutyric acid(GABA) neurons in the lateral
hypothalamus. In mice, this pro-
motes rapid approach to food
and causes eating even if the
animal has just finished a meal
and is fully sated. Marino et al.
investigated the brain circuitry
involved in such paradoxical
behavior. Stimulation failed to
drive eating through interac-
tion with GABA or dopamine
neurons in the ventral tegmen-
tal area. Instead, the authors
found that eating was elicited by
stimulation of lateral hypotha-
lamic neurons. The behavior
was mediated by a projection
that passes through the ventral
tegmental area and terminates
in a brainstem structure next
to the locus coeruleus. These
results may contribute to
our understanding of obesity
because this circuit initiates
compulsive eating in theabsence of any physiological
hunger stimulus. —PRS
Proc. Natl. Acad. Sci. U.S.A. 117 , 8611
(2020).BIOMEDICINE
The tuberculous tickle
Tuberculosis is caused by
Mycobacterium tuberculosis
(Mtb) and often manifests
with a persistent cough. This
cough is concerning not only
for the patient but also because
it provides a mechanism for
onward transmission. Coughing
often results from the activa-
tion of nociceptive neurons in
the lungs. Ruhl et al. wanted
to know how Mtb infection
induces cough in patients.
They isolated extracts from the
bacterium and applied them to
nociceptive neurons in vitro. A
specific glycolipid, sulfolipid-1
(SL-1), activated the neurons
and induced cough in guinea
pigs, but Mtb mutants that did
not synthesize SL-1 failed to
induce cough in these animals.
Thus, this bacterial molecule
appears to specifically enhance
transmissibility of Mtb. —SMH
Cell 181 , 293 (2020).AU TO CATA LYS I S
Charting the course of
the Soai reaction
The Soai reaction is unusual in
its capacity to produce just one
of two mirror-image prod-
ucts by amplifying miniscule
asymmetries at the outset.
The reaction adds an isopropyl
group from organozinc to a
specific pyrimidine-substituted
aldehyde. The product alcohol
then appears to coordinate
isopropylzinc in a tetrameric
arrangement to catalyze sub-
sequent additions. Athavale et
al. report kinetic, spectroscopic,
and modeling studies with a
simplified substrate (pyridine
in place of pyrimidine) that still
manifests autocatalysis. They
conclude that amplification
stems from better substrate
accommodation by the less
stable homochiral tetramer.
—JSY
Nat. Chem. 12 , 412 (2020).TOXINSA poisonous relationship
M
any animal species harbor microbes that provide specialized services, such as the
production of poisonous molecules that the animals can accumulate to protect them
from predation. Vaelli et al. studied the skin microbiome of rough-skinned newts, which
are known to have population-level variations in their propensity to accumulate the
ion channel blocker tetrodotoxin (TTX). They found that newts with high levels of TTX
harbored a very different set of bacterial species, including those capable of producing this
toxin. They also identified three mutations within newt ion channels that confer TTX resistance
in vitro. An important question raised by these results is whether newts can manipulate their
microbiome to cultivate the bacteria that produce TTX. —MAF
eLife 9 , e53898 (2020).Rough-skinned newts
(Taricha granulosa)
with high levels of the
poison tetrododoxin
host a distinct
set of bacteria that
produce the toxin.PHOTO: GERRY ELLIS/MINDEN PICTURES