Download - 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
070331_N_Inbriefs.indd 18070331_N_Inbriefs.indd 18 27/3/07 10:33:0627/3/07 10:33:06