Science - USA (2020-01-03)

3 JANUARY 2020 • VOL 367 ISSUE 6473 37

Edited by Caroline Ash

and Jesse Smith

IN OTHER JOURNALS

T CELL SIGNALING

Checkpoint cross-talk

Immunotherapy using antibod-

ies that block the programmed

cell death (ligand) 1 [PD-(L)1]

or cytotoxic T lymphocyte–

associated protein 4 (CTLA-4)

immune checkpoint pathways

has resulted in impressive

responses for some cancer

patients. Combined inhibition

of both pathways has generally

delivered better responses than

the targeting of either alone, but

how they functionally cross-talk

is not well defined. Zhao et al.

report that PD-L1 (the main

ligand of PD-1) and CD80 (shared

ligand for CTLA-4 and the central

costimulatory receptor CD28),

heterodimerize in cis. Using their

model system, the authors found

the PD-L1:CD80 cis complexes

to be defective in binding either

PD-1 or CTLA-4, but the abil-

ity of CD80 to activate CD28

appeared to be fully preserved.

SNOWBALL EARTH

Beating the freeze

D

espite multiple episodes during the Cryogenian period

in which the planet was mostly covered in ice for millions

of years—essentially shutting down air–sea exchange

and causing widespread ocean anoxia—marine aerobic

eukaryotes somehow survived those Snowball Earth

conditions. How did they do it? Lechte et al. show that oxygen-

ated glacial meltwater was supplied to the oceans near ice

sheet grounding lines, offering a lifeline to microbial communi-

ties there. This process may have created glaciomarine oxygen

oases that were critical to the survival and evolution of those

organisms during episodes of extreme glaciation. —HJS

Proc. Natl. Acad. Sci. U.S.A. 116 , 25478 (2019).

Artist’s conception

of a Snowball Earth

almost entirely

covered by ice

Modern example of storage organs

from a species of the Hypoxis genus,

which includes the African potato

SCIENCE sciencemag.org

PHOTO (FROM LEFT): SURADECH KONGKIATPAIBOON/ALAMY STOCK PHOTO; CHRIS BUTLER/SCIENCE SOURCE

the light and the electrons. They

show that an additional kick of

around 0.9 kilo–electron volts

(keV) can be given to a bunch

of 80-keV electrons along just

30 micrometers of a specially

designed channel. Such miniatur-

ized dielectric laser accelerators

could open up particle physics to

a number of scientific disciplines.

—ISO

Science, this issue p. 79

ARCHAEOLOGY

Middle Stone Age cooking

Early evidence of cooked starchy

plant food is sparse, yet the con-

sumption of starchy roots is likely

to have been a key innovation

in the human diet. Wadley et al.

report the identification of whole,

charred rhizomes of plants of the

genus Hypoxis from Border Cave,

South Africa, dated up to 170,000

years ago. These archaeobotani-

cal remains represent the earliest

direct evidence for the cooking of

underground storage organs. The

edible Hypoxis rhizomes appear

to have been cooked and con-

sumed in the cave by the Middle

Stone Age humans at the site.

Hypoxis has a wide geographi-

cal distribution, suggesting that

the rhizomes could have been a

ready and reliable carbohydrate

source for Homo sapiens in

Africa, perhaps facilitating the

mobility of human populations.

—AMS

Science, this issue p. 87

EVOLUTIONARY BIOLOGY

Generating a new

transcriptional network

Organismal novelties result

from changes in transcriptional

circuits. But what comes first,

changes in regulatory protein

or changes in cis-regulatory

sequences? Britton et al. exam-

ine the Mata2 protein in a

Saccharomycotina clade of

fungi. They show that a newly

evolved transcription circuit

involving repression of the

a-specific genes by the ancient

homeodomain protein Mata 2

occurred in two stages sepa-

rated by millions of years. In the

first stage, Mata2 acquired

several coding changes followed

by changes in cis-regulatory

sequences. This clade-specific

requirement explains how the

coding changes of Mata2 were

in place long before the new

a-specific gene repression circuit

arose. —BAP

Science, this issue p. 96

PARASITIC INFECTIONS

Parasite perturbation

of immunity

Helminths—a broad grouping

of parasitic worms—infect bil-

lions of people and are known

to modulate host immune

responses to promote their own

survival. De Ruiter et al. used

mass cytometry to determine

which immune cells are affected

by helminth infection. They

analyzed samples from rural

Indonesians before and after

deworming treatment. These

were compared to samples

from Europeans and urban

Indonesians, neither of which

had been exposed to helminths.

Helminths expanded specific

type 2 and regulatory immune

cells, and many immune altera-

tions reverted upon deworming.

These details on host–pathogen

interaction could inform future

targeted therapies. —LP

Sci. Transl. Med. 12 ,

eaaw3703 (2020).

Published by AAAS