Science 14Feb2020

SCIENCE sciencemag.org

IMAGE: ERIC GRAVE/SCIENCE SOURCE

such topological protection

renders the properties robust

against defects and provides a

platform of rich physics to be

studied. Recent developments

have revealed the existence

of so-called fragile topological

phases, where the means of

classification due to symmetry

is unclear. Z.-D. Song et al. and

Peri et al. present a combined

theoretical and experimental

approach to identify, classify,

and measure the properties

of fragile topological phases.

By invoking twisted bound-

ary conditions, they are able

to describe the properties of

fragile topological states and

verify the expected experimental

signature in an acoustic crystal.

Understanding how fragile

topology arises could be used

to develop new materials with

exotic properties. —ISO

Science, this issue p. 794, p. 797

REPRODUCTIVE BIOLOGY

Cellular remodeling

of the am nion

The embryo-surrounding amnion

remodels through epithelial-to-

mesenchymal transition (EMT)

and the reverse process, termed

MET. Richardson et al. found that

in amnions from mice and human

term births, EMT was greater

after labor compared with before

the onset of labor. Oxidative

stress and the inflammatory

cytokine transforming growth

factor–b, which are increased at

the end of pregnancy, promoted

EMT, whereas the pregnancy

maintenance hormone proges-

terone promoted MET. These

data suggest that oxidative stress

and inflammatory factors accu-

mulate at parturition to trigger

EMT and amnion weakening and

rupture. —AV

Sci. Signal. 13 , eaay1486 (2020).

CATALYSIS

Overcoming

surface defects

Dry reforming of methane with

carbon dioxide creates a mixture

of hydrogen and carbon mon-

oxide—synthesis gas—which

EDUCATION

Not all mentors are equal

Effective mentoring is a

critical component of scientific

training, especially at the under-

graduate level. Even though

prior research suggests that

negative mentoring experiences

are common, little is known

about mentoring experiences

in general. Limeri et al. report

on a qualitative study designed

to define and characterize

negative mentoring experiences

of undergraduate life science

researchers. Thirty-three

life science undergraduate

researchers were interviewed

about their experience with

mentors, including mentor

behaviors and characteristics

and mentoring situations and

events. The results identified

seven major categories of nega-

tive mentoring: absenteeism,

abuse of power, interpersonal

mismatch, lack of career and

technical support, lack of psy-

chosocial support, misaligned

expectations, and unequal treat-

ment. These data could be useful

to future and current mentors

reflecting on their mentoring

practice. —MMc

CBE Life Sci. Educ. 18 , ar61 (2019).

can be converted into liquid

fuels. However, heterogeneous

catalysts for this reaction are

prone to deactivation through

unwanted carbon deposition

(coking) and loss of surface area

of adsorbed metal nanoparticles

through agglomeration (sinter-

ing). Y. Song et al. used highly

crystalline fumed magnesium

oxide to support molybdenum-

doped nickel nanoparticle

catalysts (see the Perspective

by Chen and Xu). On heating,

the nanoparticles migrated on

the oxide surface to step edges

to form larger, highly stable

nanoparticles. This process also

passivated sites for coking on

the oxide to produce a catalyst

with high activity and longevity

at 800°C. —PDS

Science, this issue p. 777;

see also p. 737

STRUCTURAL BIOLOGY

Strengths and weaknesses

of an HIV drug

Retroviruses replicate by insert-

ing a copy of their RNA, which

has been reverse transcribed

into DNA, into the host genome.

This process involves the inta-

some, a nucleoprotein complex

comprising copies of the viral

integrase bound at the ends

of the viral DNA. HIV integrase

strand-transfer inhibitors

(INSTIs) stop HIV from rep-

licating by blocking the viral

integrase and are widely used

in HIV treatment. Cook et al.

describe structures of second-

generation inhibitors bound to

the simian immunodeficiency

virus (SIV) intasome and to

an intasome with integrase

mutations known to cause drug

resistance. Passos et al. describe

the structures of the HIV

intasome bound to a second-

generation inhibitor and to

developmental compounds that

are promising drug leads. These

structures show how mutations

can cause subtle changes in the

active site that affect drug bind-

ing, show the basis for the higher

activity of later-generation

inhibitors, and may guide devel-

opment of better drugs. —VV

Science, this issue p. 806, p. 810

IN OTHER JOURNALS

Edited by Caroline Ash

and Jesse Smith

ORGANOIDS

Modeling neuromuscular

biology and disease

P

roducing organs on demand is an ambitious goal for cell

and developmental biologists. The complexity of structure

and function for many organs is a difficult challenge. As

of now, organoids are the closest approximation. Faustino

Martins et al. used human pluripotent stem cells as start-

ing material to assemble neuromuscular organoids containing

spinal cord neurons, associated neuromuscular junctions,

and skeletal muscle cells. Neural and mesodermal cells were

tracked through development by single-cell RNA sequencing.

The neuromuscular organoids contracted and displayed neuro-

nal circuits and were also induced to recapitulate the pathology

of myasthenia gravis. —BAP

Cell Stem Cell 10.1016/j.stem.2019.12.007 (2020).

Magnified view of neuromuscular junctions, which are complex assemblages

of neurons and muscle cells that can now be replicated in organoids.

14 FEBRUARY 2020 • VOL 367 ISSUE 6479 753

Published by AAAS