Science - USA (2022-02-25)

SCIENCE science.org 25 FEBRUARY 2022 • VOL 375 ISSUE 6583 833

regulated by the nascent poly-

peptide–associated complex

(NAC). Jomaa et al. investigated

how NAC can prevent SRP

from binding ribosomes that

are synthesizing cytosolic and

mitochondrial proteins while at

the same time recruiting SRP

to ribosomes translating an ER

protein client. Their findings

reveal the role of NAC as a

key sorting factor for nascent

chains that helps to ensure the

specificity of membrane and

secretory protein localization in

eukaryotes. —SMH

Science, abl6459, this issue p. 839

DARK MATTER

The search for

axion dark matter

The hypothetical “axion” particle

is gaining momentum as a

candidate for explaining the

ever enigmatic “dark matter,”

which is thought to account

for about 85% of the matter in

the universe. Chadha-Day et

al. reviewed what this particle

is, and Semertzidis and Youn

reviewed how scientists are

trying to detect it. Axion dark

matter is proposed to consist

of an oscillating radiofrequency

field coupled to ordinary matter

with charge-parity violating

interactions. Detection experi-

ments use magnetic fields

to try to convert dark matter

axions into weak signals of

radiofrequency photons. New

experimental typologies and

advances in precision mea-

surement have dramatically

expanded the range of detect-

ability, and hopes are high that

they may succeed in discover-

ing the axion in the near future.

— M N A

Sci. Adv. 10.1126/sciadv.abj3618

(2022), 10.1126/sciadv.abm9928

(2022).

STRUCTURAL BIOLOGY

Movie of a moving

chloride ion

Biological pumps that use

retinal isomerization to move

protons across a membrane

have been studied extensively,

PHYSIOLOGY

How exercise

supports the brain

How does exercise enhance

neurogenesis in the adult hippo-

campus? The effect may in part

result from increased amounts

of the selenium transport protein

selenoprotein P (SEPP1) in the

serum of exercised animals. Leiter

et al. screened for proteins that

increased in abundance in mice

that exercised on a running wheel.

One of them was SEPP1, which

helps provide selenium to the

brain. Genetic depletion of SEPP1

or its receptor reduced the effect

of exercise on neural precur-

sor cell proliferation. Dietary

but the mechanisms involved

in moving chloride ions, which

have both a different charge and

different coordination require-

ments, are less well understood.

Mous et al. combined time-

resolved x-ray crystallography,

spectroscopy, and computa-

tional simulations to generate

a molecular movie of chloride

transport through a chloride-

pumping halorhodopsin. Ion

uptake from the extracellular

environment is supported by

interactions with the retinal, and

transport through a space gen-

erated by retinal isomerization

occurs within about 1 micro-

second of excitation. Release

of chloride and blockage of

backward flow is mediated

by a salt bridge that forms an

electrostatic gate at the intra-

cellular face. These insights are

important for understanding ion

transport in these pumps, which

are important tools for optoge-

netic silencing of neurons. —MAF

Science, abj6663, this issue p. 845

CANCER IMMUNOLOGY

Shared states of

tumor-specific T cells

Adoptive cell therapy is a type of

cancer immunotherapy in which

an individual’s immune system

is trained to eliminate their

tumor. This process involves

genetically engineering T cells,

but it requires the challenging

identification of T cell recep-

tors (TCRs) that can recognize

cancer-specific alterations.

Lowery and Krishna examined

TCRs from human metastatic

tumors, including those of

breast, melanoma, and colon

origin. Using TCR and single-

cell sequencing technology,

the authors found a conserved

phenotypic state common to

known tumor mutation–specific

T cells. Gene signatures were

able to predict the tumor reac-

tivity of TCRs from independent

samples and discriminate them

from bystander T cells. Such

strategies may enable more

streamlined identification of

tumor-specific TCRs for patient

immunotherapy. —PNK

Science, abl5447, this issue p. 877

NEUROSCIENCE

The elephant’s trunk

I

n the trigeminal ganglion reside cell bodies of neurons

that serve the face. For the elephant, this includes its

trunk. Purkart et al. have made an anatomical analysis

of the trigeminal system in Asian and African bush

elephants. A trunk sensory neuron can be as much as

2 meters in length and is exuberantly supported by glial cells.

The elephant’s trigeminal ganglion is larger in diameter than

its spinal cord. The infraorbital nerve, which serves the trunk,

is thicker than those serving the eye or inner ear. The authors

suggest that the unusually thick axons in the trigeminal nerve

support temporal precision, highlighting the trunk not only for

its utility in manipulating the elephant’s environment but also

for its contribution of sensory input for the elephant. —PJH

Curr. Biol. 10.1016/j.cub.2021.12.051 (2022).

Edited by Caroline Ash

and Jesse Smith

IN OTHER JOURNALS

The sensory neuron of an elephant’s trunk is up to 2 meters

in length to enable precise manipulation and sensitivity.

PHOTO: HENK BOGAARD/ISTOCK.COM