Science - USA (2021-12-03)

MECHANICAL BONDS

Pumping macrocycles

onto surfaces

Numerous chemical processes,

ranging from water purification

to catalysis, involve sorption of

small molecules onto sur-

faces. Typically, spontaneous

attractive interactions favor the

binding event. Feng et al. report

a mechanisorption process that

requires redox manipulations

to pump macrocycles from bulk

solution onto axles immobilized

on a metal-organic framework.

The resulting rotaxanes store

energy through nonequilibrium

charge concentration in their

mechanical bonds. Ultimately,

the technique could also prove

useful for actively partitioning

compounds with particular

functionality between surface

and bulk environments. —JSY

Science, abk1391, this issue p. 1215

EXOPLANETS

A nearby iron-rich

sub-Earth planet

The mass and radius of an

exoplanet determine its

mean density, which provides

information about the possible

interior structure. Lam et al.

have identified a planet on a

7.7-hour orbit around a nearby

red dwarf star. The authors

determined the planet’s radius

from the transit, then used

radial velocity observations to

measure the mass. They found

a sub-Earth–sized planet with

a density almost equivalent

to pure iron. Its high surface

temperature is close to the

vaporization point of iron, sug-

gesting that it is the iron core of

a planet that has lost its outer

mantle. —KTS

Science, aay3253, this issue p. 1271

HUMAN GENOMICS

Rare variants and blood

LDL cholesterol

A current goal in genomics is to

identify genetic variation associ-

ated with actionable traits of

clinical concern. Through exome

sequencing of an Old Order

PHYSIOLOGY

Controlling cardiomyocyte

proliferation

Mammalian cardiomyocytes pro-
liferate during development but
lose this capacity in adult life, and
this underlies the inability of the
heart to regenerate. This limita-
tion is related to cardiomyocyte
superspecialization as efficient

contractile cells. Tampakakis et al.

found that sympathetic neurons

directly repress cardiomyocyte

proliferation in mice through the

activation of transcription factors

that regulate circadian rhythm.

Cardiac sympathetic innerva-

tion develops during fetal life as

cardiomyocytes increase in size

and contractile capacity. This

maturation process is further

exacerbated postnatally, leading

to proliferation-incompetent car-

diomyocytes. This study expands

our understanding of the barriers

that restrict cardiomyocyte

proliferation and provides new

opportunities for exploring the

reactivation of heart regeneration

in mammals. —MT

Sci. Adv. 10.1126/sciadv.abh4181

(2021). PHOTO: JONATHAN BENT

1210 3 DECEMBER 2021 • VOL 374 ISSUE 6572 science.org SCIENCE

CARBON CYCLE

Up in the air

U

nderstanding ocean-atmospheric carbon dioxide (CO 2 ) fluxes in the Southern Ocean is

necessary for quantifying the global CO 2 budget, but measurements in the harsh condi-

tions there make collecting good data difficult, so a quantitative picture still is out of

reach. Long et al. present measurements of atmospheric CO 2 concentrations made by

aircraft and show that the annual net flux of carbon into the ocean south of 45°S is large,

with stronger summertime uptake and less wintertime outgassing than other recent observa-

tions have indicated. —HJS Science, abi4355, this issue p. 1275

RESEARCH

Edited byMichael Funk

IN SCIENCE JOURNALS

Aerial surveys above the ocean around Antarctica indicate greater net annual uptake

of carbon dioxide than was found by previous measurements.