Science - USA (2022-02-04)

then intercede to form car-

bon–halogen, carbon–carbon,

and carbon–sulfur bonds. A

two-step upcycling sequence

that added imidazolium groups

to postconsumer polyethylene

foam produced a potentially

valuable ionomer. —JSY

Science, abh4308, this issue p.545

DEVELOPMENTAL BIOLOGY

Deriving primitive

endoderm stem cells

The mammalian blastocyst

forms early in development and

consists of three distinct cell

types: epiblasts, trophoblasts,

and primitive endoderm (PrE).

Although stem cell lines that

retain the functional properties

of epiblasts or trophoblasts have

been established, we lack stem

cell lines that retain the develop-

mental potential of PrE, which

gives rise to extra-embryonic

lineages that nourish the embryo

and promote its development.

Ohinata et al. report derivation

of PrE stem cells that are able to

NEUROSCIENCE

Unmasking place fields

in hippocampal CA1

A basic transformation process

in the brain is the conversion

of a neuron’s excitatory and

inhibitory inputs to spikes.

Experimentally examining

the transformation process

requires access to subthresh-

old membrane dynamics. To

date, only intracellular record-

ings have met this requirement.

Valero et al., using a new tech-

nique based on optogenetic

stimulation to probe the excit-

ability of neurons, examined the

subthreshold activity dynamics

of CA1 pyramidal neurons dur-

ing sharp-wave ripples, theta

oscillations, and place fields.

During sharp-wave ripples,

overall excitability shifted

toward synaptic inhibition.

However, during theta waves

and in the center of place

fields, excitability moved in the

direction of synaptic excitation.

This stimulation unmasked the

place fields of nonplace cells,

indicating that the proportion

of place cells in CA1 is much

higher than previously thought.

—PRS

Science, abm1891, this issue p. 570

NEUROGENOMICS

Genes control cortical

surface area

Humans exhibit heritable

variation in brain structure and

function. To identify how gene

variants affect the cerebral cor-

tex, Makowski et al. performed

genome-wide association stud-

ies in almost 40,000 adults and

9000 children. They identified

more than 400 loci associated

with brain surface area and

cortical thickness that could

be observed through magnetic

resonance imaging analy-

ses. Examining the biological

pathways linking gene vari-

ants to phenotypes identified

region-specific enrichments of

neurodevelopmental functions,

some of which were associ-

ated with psychiatric disorders.

Partitioning genes with heritable

variants relative to evolutionary

conservation helped to identify

a hierarchy of brain develop-

ment. This analysis identified a

human-specific gene-phenotype

association related to speech

and informs upon what genes

can be studied in various model

organisms. —LMZ

Science, abe8457, this issue p. 522

ORGANIC CHEMISTRY

A clean break for

C–H bonds

Carbon–hydrogen (C–H) bonds

are ubiquitous in pharma-

ceuticals and plastics but are

difficult to transform. Fazekas

et al. report a versatile reagent

that strips hydrogen without

immediately trapping the

carbon. Heating or photoly-

sis of the reagent produces a

pair of radicals, one of which

rapidly cleaves a C–H bond

while the other remains com-

paratively inert. A wide variety

of other radical sources can

RESEARCH

Edited by Michael Funk

IN SCIENCE JOURNALS

Self-assembly of hydroxyapatite nanowires can produce an artificial analog of

enamel, the hard biomineral that covers the surface of the teeth.

PHOTO: ALEXSHOR/ISTOCK.COM

SCIENCE science.org 4 FEBRUARY 2022 • VOL 375 ISSUE 6580 509

MATERIALS SCIENCE

Artificial enamel analog

T

ooth enamel is the thin outer layer of our teeth and is the

hardest biological material in the human body. Zhao et al.

engineered an enamel analog consisting of assembled

hydroxyapatite nanowires with amorphous intergranular phase

segments aligned using scalable, dual-directional freezing in the

presence of polyvinyl alcohol. The artificial tooth enamel was designed

to closely mimic the composition of the natural material by copying

the shapes and sizes of the components found biologically and the

organization of their interfaces. —MSL Science, abj3343, this issue p. 551