Science - USA (2020-08-21)

SCIENCE sciencemag.org 21 AUGUST 2020 • VOL 369 ISSUE 6506 931

associated with tumor cells.

They found that a type of intes-

tinal bacteria called enterococci

harbor a bacteriophage that

modulates immune responses.

In mouse models, administra-

tion of enterococci containing

the bacteriophage boosted

T cell responses after treatment

with chemotherapy or pro-

grammed cell death protein 1

(PD-1) blockade. In humans, the

presence of the bacteriophage

was associated with improved

survival after PD-1 immunother-

apy. A fraction of human T cells

specific for naturally processed

melanoma epitopes appeared

to be able to recognize micro-

bial peptides. This “molecular

mimicry” may represent cross-

reactivity between tumors and

microbial antigens. —PNK

Science, this issue p. 936

LIQUID CRYSTALS

Controlling the curvature

Molecular chirality is often

required to make chiral liq-

uid crystalline phases, but

liquid crystallinity has also been

obtained using curved elon-

gated rods known as bent-core

or banana-shaped molecules.

Fernández-Rico et al. developed

a method to controllably alter the

curvature of the rods using ultra-

violet light and a photoresponsive

polymer (see the Perspective by

Godinho). From a single starting

batch can come a family of rods

with different curvatures but

similar overall rod thickness,

length, and length distribution.

The researchers explored a

range of liquid crystalline phases,

including the splay-bend nematic

M U TAT I O N

Calibrating mtDNA

mutations through age

Mitochondrial DNA (mtDNA)

is a separate genome found in

eukaryotic cells that is mater-

nally inherited. Mutations in

mtDNA underlie several human

diseases, and the accumula-

tion of these mutations has

been associated with aging.

Arbeithuber et al. used duplex

sequencing to trace accumula-

tion of spontaneous mtDNA

mutations in oocytes, brain,

and muscle cells of mice. Ten-

month-old mothers showed a

two- to threefold increased rate

of mtDNA mutation compared

with their 1-month-old pups. The

authors found that the D-loop, a

stretch of triple-stranded highly

variable DNA in the noncoding

region of the circular mtDNA

where replication initiates,

accumulated the most muta-

tions. These mtDNA mutations

occurred in patterns, indicating

that they were caused by replica-

tion errors. It is possible that

inheritance of aged mtDNA from

older mothers may have health

consequences for their offspring.

—LMZ

PLOS BIOL. 18 , e3000745 (2020).

phase that was predicted more

than 40 years ago. —MSL

Science, this issue p. 950;

see also p. 918

IMMUNOLOGY

SOSTDC1 for germinal

center regulation

T follicular helper (TFH) cells are

CD4+ T cells that facilitate B cell

antibody production and B cell

memory responses in the ger-

minal centers (GCs) of lymphoid

organs. These activities are in

turn restrained by T follicular

regulatory (TFR) cells, a population

of T cells with unclear origins.

Wu et al. now demonstrate that

a subpopulation of TFH cells and

fibroblastic reticular cells both

produce sclerostin domain-

containing protein 1 (SOSTDC1),

which drives TFR cell generation

by inhibiting Wnt–b-catenin

signaling. In mice lacking the

gene Sostdc1, TFR cell numbers

were substantially decreased and

GC responses were enhanced.

These insights into TFR cell

biology and GC regulation may

have important implications for

autoantibody-mediated diseases

and the future development of

vaccines and therapies for auto-

immune disease. —STS

Science, this issue p. 984

CHEMICAL PHYSICS

Attosecond science in

liquid phase

Many physical properties of

liquid water remain unresolved

due to the very fast dynamics

involved in the liquid phase.

Using attosecond time-resolved

photoelectron spectros-

copy, Jordan et al. found that

photoemission of electrons

from water in the liquid phase

shows a time delay of about 50

to 70 attoseconds compared

with photoemission from the

gas phase. This difference was

attributed to solvation effects

and was validated by analysis

of various contributions to the

measured delays and by using

theoretical simulations in water

clusters of different sizes. —YS

Science, this issue p. 974

PLANT ECOLOGY

Let the grass grow old

O

ver the past decade, there has been a reappraisal of the

importance of grasslands in the global ecosystem. While

they have often been regarded as a successional step en

route to forest and woodland, there is increasing recogni-

tion of the conservation value of old-growth grasslands.

Nerlekar and Veldman synthesized data on species richness

in grasslands worldwide, showing that old-growth grasslands

display high plant species diversity and that weedy secondary

grasslands can take centuries to recover old-growth richness.

They conclude that old-growth grasslands should be priori-

tized for conservation for their value in providing ecosystem

services and supporting herbivore populations, analogous to

the values perceived in old-growth forest. —AMS

Proc. Natl. Acad. Sci. U.S.A. 117 , 18550 (2020).

Curved nanorods, observed by confocal

microscopy, adopt dif erent phase

behavior depending on their curvature.

Old-growth grasslands are highly diverse, support herbivores, and provide

important ecosystem services that are vulnerable to damage.

CREDITS (FROM LEFT): FERNÁNDEZ-RICO

ET AL.;

CATHERINE WITHERS-CLARKE/ISTOCK

Edited by Caroline Ash

and Jesse Smith

IN OTHER JOURNALS

Published by AAAS