present, but it’s inadequate,”

he says. “Could that be because

mammals don’t have enough

[heart] stem cells? We need to

understand what is holding the

system back so that we can devise

a strategy to turn that brake off.”

But Kenneth Chien of the

Massachusetts General Hospital

in Boston isn’t convinced. “The

most important question now is:

can you identify that new pool?

Are they pre-existing immature

cardiac muscle cells? Or are they

[stem cells] from the heart or

elsewhere in the body?”

remained the same, suggesting

that adult mice don’t normally

make new heart muscle cells.

When the team induced heart

attacks in the mice, the number

of stained cells dropped to 70 per

cent, while the overall number of

heart cells remained about the

same, suggesting that new muscle

cells can form in response to

injury (Nature Medicine, DOI:

10.1038/nm1618).

Lee thinks that the adult

mouse heart has a limited ability

to repair itself. “The mechanism

to activate cardiac regeneration is

TATOOINE, eat your heart out. The

fictional planet in Star Wars that orbits two suns stands to be

upstaged by a quadruple star

system 150 light years from Earth

that may host a planet.

The system, called HD 98800,

consists of two pairs of stars in

which the partners in each pair

orbit one another and the pairs in

turn travel around each other.

Observations by the Spitzer Space

Telescope show two concentric

rings of dust around one of the

pairs, which suggests a planet

may be circling there.

Elise Furlan of the University

of California, Los Angeles, and

colleagues say the empty space

between the two rings might have

been cleared out by the gravity of

a planet orbiting there. One ring

lies about twice as far as the Earth

lies from the sun, while the other,

which is denser, lies about six

times the Earth-sun distance.

Since any coalescence in the

dust is not expected to be stable

at the location of the inner ring,

Furlan says if there is a planet, it

is more likely to be found near the

outer ring. However, it is possible

the region between the rings

could simply have been cleared by

the gravity of the four stars.

Four-star lodgings

for a planet

MOTORISTS are not the only ones to

benefit from high-speed roads. Life

in the fast lane also helps plant seeds

travel far from home. So say Moritz

von der Lippe and Ingo Kowarik of

the Technical University of Berlin,

Germany, who have shown that

traffic may account for up to half of

seed dispersal near motorways.

Seeds may stick to vehicles or be

swept along in the airflow created by

traffic. To find out how common this

is, the researchers left seed traps deep

within several long road tunnels,

ensuring that the seeds collected were

transported by vehicles rather than

the wind. Over a year, they trapped

more than 6000 seeds, from which

they calculated that vehicle transport

is responsible for between 635 and

1579 seed falls per square metre

per year. That is roughly the level

of natural seed fall in sparsely

vegetated areas, suggesting that

vehicle transport could double

the effectiveness of seed dispersal

if such areas are near busy roads

(Conservation Biology, DOI: 10.1111/

j.1523-1739.2007.00722.x).

Among their samples, von der

Lippe and Kowarik found seeds from

39 problematic invasive species that

are damaging biodiversity in some

parts of the world. “Many countries,

including the US, spray roadsides with

herbicides,” says von der Lippe.

DO YOU remember life’s highs and

lows? If not, perhaps you can blame

your genes. It looks as if a gene that

influences how brains respond to

neurotransmitters may affect our

ability to recall emotional events.

Such incidents trigger the release

of noradrenalin, which stimulates

memory storage, says Dominique de

Quervain at the University of Zurich

in Switzerland. Since the ability to

recall emotional events varies from

person to person, he wondered if

a variant of ADRA2B, the gene that

codes for the noradrenalin receptor,

could be involved.

To find out, his team selected

photos of various events, some

unlikely to rouse emotions, others

with a strong emotional charge,

positive or negative. Then they

showed the pictures to two large

groups of people and later asked

them which ones they remembered.

One group comprised traumatised

survivors of the Rwandan genocide,

the other healthy Swiss citizens. In

both groups, people with the ADRA2B

variant were “substantially more

likely” to remember both positive

and negative images than people

with other forms of the gene (Nature Neuroscience, DOI: 10.1038/nn1945).

However, the Rwandans with the

variant had far higher recall of the

negative emotional events in the

experiment than the Europeans who

carried it. The variant is carried by

30 per cent of Caucasians and 12 per

cent of Africans.

THE discovery of heart stem cells

in 2006 raised hopes that new

treatments for heart disease

would soon follow. Now, it seems

heart stem cells may already help

to repair the damage after a heart

attack, if only to a limited degree.

Richard Lee of the Harvard

Medical School and colleagues

genetically engineered mice so

that their heart muscle cells could

be stained with a fluorescent

protein. Only 80 per cent of the

heart muscle cells in young mice

picked up the stain. However,

as the mice aged, this level

PUNC

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The heart can repair itself – up to a pointMemories are made of this

Beware invasion by hitch-hiking seeds

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