no signs of life… just an old plate

In brief–

Richard ffrench-Constant

of the University of Exeter in

Penryn, Cornwall, in the UK and

colleagues confirmed that the

resistance is due to the LTR

by showing that it increases

expression of Cyp6g1 in tissues

where detoxification takes place.

Ffrench-Constant says it is “scary”

that Accord has exactly the same

mode of expression as Cyp6g1

and that it landed in exactly the

right spot in the genome.

“It’s enough to make you

believe in God,” ffrench-Constant

says. “Not that I do.”

cytochrome P450, things got

interesting. Accord copied itself

and jumped out again, leaving

behind a 149 base-pair footprint –

a section of DNA called a long

terminal repeat (LTR).

This LTR just happens to

express itself in exactly the same

way as Cyp6g1. With double the

gene expression, double the

amount of detoxification agent

was made – and the insect became

resistant to the insecticide

DDT, as well as a whole slew of

new insecticides (Genetics, DOI:

10.1534/genetics.106.066597).

A HUNT for signs of the earliest

life on Earth has instead turned

up the earliest evidence yet for

plate tectonics. This pre-dates

previous evidence by more than a

billion years and will go some way

to settling a debate about whether

plate tectonics began early in

Earth’s history, or much later.

Until now, the earliest

evidence for the theory – which

describes the motion of the plates

that make up the Earth’s crust –

came from the discovery of

2.5-billion-year-old “ophiolites”.

These are a distinctive sequence

of rocks from the ocean floor that

end up on land and are regarded

as a sign of plate tectonics.

Harald Furnes of the University

of Bergen in Norway and his

colleagues were looking for signs

of life in the Isua supracrustal

belt, a 3.8-billion-year-old rock

formation in south-western

Greenland. Instead they found

“sheeted dikes”, the banded rocks

that make up ophiolites, and

rocks nearby resembling those

beneath islands that sit above

today’s subduction zones – where

one plate slides beneath another

(Science, vol 315, p 1704). This

suggests plate tectonics got going

at least 3.8 billion years ago.

No signs of life… just an old plate

Mammals not such late developersTHE demise of the dinosaurs led to

an evolutionary explosion of modern

mammals – or so we thought. It

now seems that most mammalian

lineages were around well before the

dinosaurs died out, perhaps being

held in check by other mammals.

From the fossil record alone, it

looks as if the ancestors of most living

mammals arose in a sudden burst

of evolutionary divergence soon

after the Cretaceous period ended

65 million years ago, filling ecological

gaps left by the extinct dinosaurs.

To check this, Olaf Bininda-Emonds

of the Technical University of Munich,

Germany, and colleagues drew up an

evolutionary “supertree” of 4510 of

the 4554 living species of mammals

and used fossils, DNA and statistical

estimation to date the branching

points over the past 150 million years.

The supertree shows that

diversification did not in fact speed

up at the end of the Cretaceous.

Instead, the evolutionary branching

of mammals was thickest about

93 million years ago, while dinosaurs

were still in their prime (Nature,

vol 446, p 507).

A second burst of diversification

beginning about 50 million years ago

may have resulted from the extinction

of other, more primitive mammal

groups, which may have suppressed

the radiation of advanced mammals.

Relief in sight for severe back painMANY people get back pain at some

point in their lives. But some of us

are unlucky enough to develop

severe degenerative disc disease,

which can be truly debilitating. Now

it seems that disc transplants from

dead donors could be used to treat

the problem.

Spinal discs connect individual

vertebrae and have a jelly-like

centre that acts as a shock absorber.

Over time, the discs can dehydrate

and become less compressible,

causing severe pain.

The usual treatment is painkillers

and physical therapy. The last resort

is spinal fusion, an operation in

which two vertebrae are fused

together, but this can lead to

decreased mobility and degeneration

of discs between nearby vertebrae.

Keith Luk of the University

of Hong Kong and Dike Ruan of the

Naval General Hospital in Beijing,

China, used donor discs to replace

damaged ones in the neck regions of

one woman and four men. Five years

later, symptoms such as numbness,

muscle weakness and stiffness of gait

had improved in all the patients (The Lancet, vol 369, page 993).

Importantly, none of the patients

had an immune response to the

foreign tissue, even though

immunosuppressive drugs were not

used. “Anatomically this is a special

tissue. There is no blood supply to

the centre of the disc bringing in

immune cells,” says Ruan.

SELFISHNESS is not always a bad

thing. Selfish DNA has caused an

entire species to become resistant

to a range of insecticides in just

40 years.

That’s some feat when the

species is the almost ubiquitous

fruit fly, Drosophila melanogaster.

Even more remarkable is the way

it happened. The bit of selfish

DNA involved, called Accord, is a

transposable element that jumps

around the fruit fly genome

copying itself. When Accord landed

in Cyp6g1, a gene that makes a

detoxification agent called

NEIL

BOR

DEN/

SPL

DAVE

WAT

TS/N

HPA

How selfish DNA saved the fruit fly

18 | NewScientist | 31 March 2007 www.newscientist.com

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