CLARITY leaves tissue sturdy enough for scientists to

infi ltrate it repeatedly with labels for specifi c cell types,

neurotransmitters, or proteins; wash them out; and image

the brain again with different labels. Researchers say the

advance could speed up by 100-fold tasks such as count-

ing all the neurons in a given brain region and could make

traditional methods of imaging postmortem brain tissue

irrelevant. At present, however, the technique is limited to

small amounts of tissue: Just clarifying a 4-mm-diameter

mouse brain takes about 9 days.

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Researchers unveiled the most complete skull of an early human ancestor this past November—and proved once again that a single fossil can transform our picture of human ancestors. The stunning 1.8-million-year-old remains of a mature male had a remarkably small brain and a large, jutting jaw. That’s just the opposite of what researchers expected to fi nd for members of our

genus Homo at this time. Four skulls of our direct ancestor, Homo erectus, found in the same sliver of time and place—at Dmanisi in Georgia—had bigger brains and less con-spicuous mugs. As a result, the latest Dmanisi skull, which even includes the fragile midface bones, has given early Homo a new visage.

If it, too, is a member of H. erectus, as the researchers think, that species had more diversity in brain size and facial traits than previously believed. New dating of the skull

and its four companions also suggests that H. erectus left Africa soon after it appeared there 1.9 million years ago.

But some paleoanthropologists suggest the skull could belong to Homo

habilis, a more distant earlier human ancestor that lived in Africa about 2.3 million to 1.4 million years ago. Or it could belong to a new species. Regardless of the skull’s precise identity, its remarkable preservation will make it an icon for the face of early Homo for decades, if not centuries, to come.

Turns out humans weren’t the fi rst organism to gear up to gain a power-ful mechanical advantage. In September, high-speed videos revealed that

immature Issus coleoptratus planthoppers are such great leapers because of toothy interacting gears on their rear legs. By meshing together, the gears cock and coordinate the legs prior to and during each explosive hop.

They will never win a beauty contest, but naked mole rats (Heterocepha-

lus glaber) may hold a lesson or two for humans. Two studies this year, for instance, found clues to why these rodents can live 30 years, cancer-free. One secret may be a ribosome that excels at producing error-free proteins; misformed proteins can clog up the body’s systems and accelerate aging. Another could be a supersized ver-sion of a complex sugar that seems to pro-tect against cancer. Naked mole rats don’t break this compound down as fast as other animals, so it builds up in the spaces between cells and may keep the cells from clumping together and forming tumors.

Dmanisi Skull Gives New Face To Early Human Ancestors

Top-Gear Planthopper

The Rat That Ages Beautifully

F O S S I L O F T H E Y E A R

I N V E RT E B R AT E O F T H E Y E A R

1435www.sciencemag.org SCIENCE VOL 342 20 DECEMBER 2013

BREAKTHROUGH OF THE YEAR 2013 | NEWSFOCUS

that system, called TALENs (for transcription activator-like

effector nucleases), prompted Science to recognize genome

editing as one of the major achievements of 2012.

CRISPR, which stands for clustered regularly inter-

spaced short palindromic repeats, takes genome editing to

the next level. The name comes from repetitive stretches

of DNA that bacteria have evolved as part of an adaptive

immune system against viruses called bacteriophages. To

fi ght these viruses, bacteria link the protein Cas9 to RNA

that matches the virus’s genome. The complex cuts the

viral DNA, disabling it. In 2012, researchers fi rst used lab-

made CRISPR complexes for genome editing in a test tube.

Others immediately recognized CRISPR’s potential. With

TALENs or zinc fi nger nucleases, each new gene targeted

requires a custom protein be built. CRISPR substitutes

RNA—which is simpler to make than a piece of a protein—

for the DNA-targeting section.

Researchers are eagerly tinkering with CRISPR tech-

nology; they are modifying the Cas9 protein so that it nicks

instead of cuts the DNA. Biochemists are also working out the

structures of the Cas9 complexes. And a few labs are explor-

ing whether other Cas proteins might work better than Cas9.

To take CRISPR from basic research to medicine—

harnessing it to fi x a broken gene or disable a bad one, for

example—researchers must show that each CRISPR con-

struct hits only its target and no others. For now, CRISPR

RNA will sometimes latch on to DNA that doesn’t exactly

match up. But CRISPR researchers are already finding

ways to sharpen their targeting.

Both CRISPR and TALENs were unanticipated out-

comes of basic research unrelated to genome editing.

So CRISPR could easily be displaced by an even slicker

genome-editing tool. But for now, with companies form-

ing and new studies coming out practically every week, the

CRISPR craze is in full swing.

V E RT E B R AT E O F T H E Y E A R

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Thirty-six years out from Earth, its power dwindling and several instruments dead, the Voyager 1 spacecraft has left the invisible cocoon spun by the sun and entered interstellar space. So concluded Voyager team leaders and most space physicists in September. But it had taken them a year to realize Voyager had broken out of the heliosphere—the bubble infl ated by the sun’s wind of charged particles. That is a testament to just how weird the outer “edge” of the solar system proved to be.

Team members had a checklist of indicators that would confi rm that Voyager 1 had crossed into interstel-lar space. The density of plasma—the soup of low-energy charged and neu-tral particles pervading space—should jump, cosmic rays produced within the heliosphere should drop while those of interstellar space should increase sharply, and the direction of the magnetic fi eld that pervades all space should switch. Voyager couldn’t detect any change in plasma density, because its plasma instrument failed shortly after passing by Saturn. It did measure the expected changes in cosmic rays, in August 2012. But it never saw the magnetic fi eld switch. So the offi cial team line had Voyager in a “depletion region” still within the heliosphere.

There, Voyager would have remained if not for a little help from the sun. Twice it sent a solar blast out Voyager’s way, setting off oscillations in the plasma that the spacecraft’s plasma wave instrument could detect, giving team mem-bers a proxy for plasma density. Extrapolating back, they could see that the plasma density had shifted in August 2012, just when cosmic rays had switched. Team leaders concluded that Voyager 1 had actually entered interstellar space at that time, even though the magnetic fi eld did not shift.

That interpretation will be tested as Voyager 2, a few years behind its sibling, brings its operating plasma instrument to bear on the same region.

Voyager Is Really Out There, Somewhere

U.S. Representative Lamar Smith (R–TX) likes to recall how a “D” in a fresh-man physics class at Yale University taught by a former presidential science adviser, D. Allan Bromley, caused him to switch his major to American studies

—and started him on the road to a career in politics. Now, the tables have turned: This year, Smith gave a failing grade to the National Sci-ence Foundation (NSF) as part of a controver-sial attempt to reshape U.S. science policy that has scientists talking.

As the new chair of the House of Represen-tatives science committee, Smith has drafted legislation that would alter how NSF manages peer review. He says the proposed changes would make the system more transparent and ensure that tax dollars are being spent

wisely. But science leaders view the bill as a threat to a system that has fueled 60 years of innovation—and that other nations are trying to copy.

In a bid to preempt the draft legislation, this month NSF announced plans to sharpen its descriptions of funded grants to emphasize their relevance to important societal goals. Will it be enough?

Chairman Smith Versus the Scientists

P O L I T I C O O F T H E Y E A R

BREAKTHROUGH OF THE YEAR 2013 | NEWSFOCUS

induced pluripotent stem (iPS) cells to become neural

stem cells. Then they suspended clumps of the cells

in a gelatinous material called Matrigel and let them

grow in a bioreactor, which rotates to help nutrients

reach the cell clusters.

To the scientists’ surprise, after a few weeks they

saw darker pigmented cells that seemed to resemble

early eye development. On closer inspection, they

found evidence that the organoids had developed lay-

ers identifi able as forebrain, midbrain, and hindbrain,

all typical of fetal brains. They also saw evidence

for an outer subventricular zone, which is present in

human brains but not mouse ones.

The mini-brains have already yielded insights into

microcephaly, a condition in which the brain doesn’t

grow to its full size. When the team started with iPS

cells derived from a microcephaly patient, the result-

ing organoids were smaller than normal because stem

cells stopped dividing too soon. With further devel-

opment, researchers hope to use the mini-brain tech-

nique to investigate other brain diseases.CR

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Going, gone. Voyager 1 (top) has exited the heliosphere in this artist’s conception, while Voyager 2 (bottom) is getting close.

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February’s window-shattering explo-sion over Chelyabinsk, Russia, terri-fi ed thousands and caused hundreds of injuries, mostly minor. It also provided a windfall for scientists and a public relations bonanza for asteroid hunters.

For scientists, the midair self-destruction of a 19-meter-diameter rock provided a key benchmark for re-evaluating the threat from such relatively small visitors from the asteroid belt. Researchers had plenty of observations to work with. Data came from 400 public and private video cameras, seismographs, ground-based sensors that record ultra-low-frequency sound, and satellites intended to catch clan-destine nuclear tests.

The Chelyabinsk blast had an energy equivalent of about 500 kilotons of TNT, researchers estimate, or about 23 times the energy of the nuclear bomb dropped on Nagasaki. Initially, that output appeared to make the airburst a rarity, far larger than expected by astronomers who use telescopic surveys to gauge asteroid hazards. But after researchers compared the sound and bright-ness of Chelyabinsk with other meteor airbursts over a 20-year period, they found that big airbursts are at least three times—and perhaps 10 times—more frequent than astronomers thought.

The incident energized those eager to fi nd other small asteroids, whether heading for Earth or passing nearby. NASA is cranking up its search effort because it wants to fi nd an asteroid smaller than 10 meters for an astronaut rendezvous. The nonprofi t B612 Foundation wants to fl y a spacecraft-borne telescope to help with that mission and search for hazardous asteroids, if someone will provide the funding.

In June, the U.S. Supreme Court reversed three decades of policy—and rattled the biotech world—when it ruled that human genes cannot be pat-ented. The case, Association for Molecular Pathology v. Myriad Genetics, pitted a Utah company that owns patents on the human breast cancer genes BRCA1 and BRCA2 against doctors and researchers who argued that the patents were

invalid and stifling research. The court agreed unanimously, fi nding that human genes are a “product of nature” and so not patentable.

It will take years for the full consequences of this rev-olution in legal thinking to become clear. But the deci-sion is already making waves. It

spurred several companies to offer breast cancer diagnostic tests that competed with Myriad’s—sparking a contentious new legal battle. And in October, fed-eral Judge Susan Illston in San Francisco cited the Supreme Court’s reasoning in striking down another DNA patent, involving a Down syndrome test developed by Sequenom of San Diego, California. Sequenom plans to appeal, and it is likely that many companies will be asking judges to clarify exactly how the law defi nes a product of nature.

Siberian Meteor Blast Delivers a Warning Shot

U.S. High Court Bars Human Gene Patents

B R E A K U P O F T H E Y E A R

R U L I N G O F T H E Y E A R

www.sciencemag.org SCIENCE VOL 342 20 DECEMBER 2013

BREAKTHROUGH OF THE YEAR 2013 | NEWSFOCUS

application for which near-perfect crystals are de rigueur.

Crystalline quality is central to a solar cell’s ability to pro-

duce power. When sunlight strikes a cell, it energizes elec-

tric charges. This propels them through the material to the

electrodes, where they are collected and sent through wires

as an electric current. Defects in semiconductor crystals act

as speed traps. Perovskites offer a cheap route to fewer traps.

But perhaps the best news about perovskite solar cells is

that it may be possible to integrate them with conventional

silicon solar cells, layering the newbies right on top of sili-

con panels. Perovskites excel at snagging the higher energy

photons in sunlight—the blues and greens—while silicon

does better at grabbing the lower energy red and infra-

red photons. So putting the two together in a hybrid could

achieve an effi ciency of as much as 30%. Solar research-

ers around the globe are racing to marry the two materials.

They’re also coping with potential problems. Solar

cell perovskites are fragile and readily break down when

exposed to water or air. The current varieties also contain

lead, an environmental toxin. To make a viable technology,

researchers will have to fi nd ways to encapsulate the materi-

als, and fi nd safer replacements. If the rapid progress so far

can be sustained, perovskites’ star has only begun to rise.

hasn’t been easy. Because they’re electrically charged, protons

and nuclei swirl in interstellar magnetic fi elds. So by the

time they reach Earth, cosmic rays do not point back to their

birthplaces. The Fermi team had to fi nd another way to show

that supernova remnants accelerate the particles.

If protons are accelerated in a supernova remnant, then

a few proton-proton collisions should still occur. Such

collisions produce fl eeting particles called pi-zero mesons,

each of which quickly decays into a pair of high-energy

photons. Those pi-zero decays should then produce a telltale

hump in the energy spectrum of photons from a supernova

remnant, when it’s plotted in a particular way. After 5 years

of collecting data, Fermi researchers spotted that signature of

proton acceleration in two supernova remnants. They had to

tease it out of the overwhelming glare of photons that ricochet

off high-energy electrons, which do not have such a spectral

bump. Others had looked for the signature, but Fermi is the

fi rst experiment to see it clearly.

Astrophysicists still don’t know many details of how

the particles and magnetic fi elds interact, and they suspect

that the highest energy cosmic rays originate from other

sources outside our galaxy. Still, there’s now no doubting that

supernova remnants do indeed spew cosmic rays.

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In May, for the fi rst time in recorded history, atmospheric concentrations of carbon dioxide rose above 400 parts per million, dramatiz-ing the failure of governments to limit green-house gas emissions. • The same month, a second reaction wheel failed on the Kepler planet-hunting spacecraft, dooming its abil-ity to point accurately and collect precise data. • In October, congressional gridlock on spend-ing issues forced the U.S. government to

partially shut down for 16 days, paralyzing science funding agencies, disrupting research projects, and canceling many Antarctic fi eld studies. • More than one-half of 304 free open-access journals accepted a bogus paper submitted by Science journalist John Bohannon, who sparked fi erce debate over the quality of peer review when he reported his sting. • By year’s end, disgraced Dutch social psychologist Diederik Stapel had retracted at least 54 papers based on made-up data, but was giving a TED talk about his misconduct.

Notable sequences of 2013: The oldest human mitochondrial DNA, which comes from a 400,000-year-old Neandertal ancestor found in Spain but mys-teriously resembles that of a different extinct human • The oldest organis-mal genome, from a 700,000-year-old fro-

zen horse hoof • Other complete genomes came from the comb jelly, changing views of the animal tree of life • Minke whale, reveal-ing how marine mammals cope with deep dives • Amborella, sister to all fl owering plants, explaining the early days of angiosperms • Tiger, lion, and snow leopard, capturing the

genomic essence of big cats • The scorpion Mesobuthus martensii (at right), which has 10,000 more genes than humans do • Norway spruce (Picea abies), white spruce (Picea glauca), and, soon, loblolly pine (Pinus taeda), each with genomes about seven times the size of a human’s—a sequencing tour de force • The invaluable HeLa cancer research

cell line, requiring permission from the family of Henrietta Lacks • King cobra and Burmese python, telling an evolutionary tale of extreme adaptations • Four bats which, when compared to dolphins, highlight a common core of echolocation genes • Pigeon, revealing the gene for crests • Irish famine

potato blight, showing that this historic strain is extinct.

Breakdowns of the Year

Genomes of the Year

A L S O N OT E D

In January, one of the world’s fi rst nanofactories made its debut. Researchers built a molecular machine that mimics the cell’s protein-building factory, the ribosome, but is one-tenth the size. This ribosome robot includes a molecu-

lar axle track with a ring around it. When heated, the ring’s sulfur-containing amino acid sequentially grabs each of three amino acids from the track to build a short pep-tide chain. The machine has been hailed as ingenious, but it won’t replace ribosomes anytime soon. It takes days to do what the real ribosome can do in tenths of a second.

Ribosome Robot

BREAKTHROUGH OF THE YEAR 2013 | NEWSFOCUS

verts melamine to a form that collects in the kidney. About

1% of infants carry Klebsiella—about the same percent-

age of infants on milk formula who got sick, suggesting this

microbe may play a role in human toxicity as well.

• In Malawi, researchers studied unusual cases in which

one twin developed a malnutrition syndrome called

Kwashiorkor but the other did not. They sampled the chil-

dren’s microbes for 3 years, tracking how the bacterial

populations changed before, during, and after treat-

ment with a nutritional supplement. They also implanted

fecal material from each twin into the guts of germ-free

mice and then monitored the animals over several weeks.

Mice that received bacteria from the Kwashiorkor chil-

dren developed Kwashiorkor-like symptoms; other mice

did not. The researchers discovered that the malnourished

children’s microbial portfolio had not matured properly.

As a result, they suggest, the children were less able to

process amino acids containing sulfur and thus were more

prone to malnutrition.

• This year, researchers traced several links between gut

microbes and cancer. Three anticancer therapies proved to

need gut bacteria to be effective; the bacteria help prime

the immune system to respond to drug treatment. A mouse

study showed that a liver cancer often associated with

obesity can arise because of a DNA-damaging bacterial

byproduct that builds up in obese mice. Finally, new results

confi rmed earlier hints that a gut bacterium called Fusobac-

terium plays a role in stimulating colorectal tumors.

• In a study of obese mice, the animals lost weight and

had better insulin control—even on a high-fat diet—when

researchers boosted the amount of the mucus-eating gut

bacterium Akkermansia muciniphila in their guts. Obese

mice, as well as obese people and people with type 2 diabe-

tes, typically have reduced numbers of these bacteria. The

same bacterium also seems to play a role in the weight loss

that accompanies gastric bypass surgery.

The year also saw more tantalizing hints of microbial

infl uences on immune system function. The autoimmune

disease rheumatoid arthritis, for example, may be asso-

ciated with a bacterium called Prevotella copri. In mice,

increases in the bacterium Lactobacillus johnsonii in the

gut account for much of the protection against allergies and

asthma provided by exposure to indoor/outdoor dogs and, to

a lesser extent, cats.

The studies make it increasingly clear that personal-

ized medicine will need to take our microbial guests into

account to be most effective.

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