[情報] Chimpanzee joins the genome club
http://www.nature.com/news/2005/050829/full/050829-9.html
Published online: 31 August 2005; | doi:10.1038/news050829-9
Chimpanzee joins the genome club
Genetic sequence could show just how we differ from other apes.
Michael Hopkin
Blood samples from single chimp, called Clint, provided 98% of the genome
data. (c) Yerkes National Primate Research Center
Geneticists have finished reading one of the most important volumes in the
library of life: the DNA of the chimpanzee. Decoding the sequence of our
comrade in apehood may help to answer the age-old question of what makes us
human.
The US-led Chimpanzee Sequencing and Analysis Consortium, which presents the
sequence in this week's Nature1, has already begun making such comparisons. By
lining the Pan troglodytes sequence up against the human genome, it has
spotted six areas of our own DNA that have been rigorously sculpted by natural
selection. The areas include one that contains a gene known to be crucial
for that most human of traits, speech.
"We have targeted regions of genes that look like they'll be really
important for investigating the differences between chimps and humans," says
consortium member Evan Eichler of the University of Washington School of
Medicine in Seattle.
In the lists
The chimpanzee joins an extensive roster of species that have been given the
genome-sequencing treatment. The list now numbers in the hundreds, including a
host of bacterial species and pathogens, the mouse, rice, and family
favourites such as the dog.
We have targeted regions of genes that look like they'll be really
important for investigating the differences.
Evan Eichler
University of Washington School of Medicine, Seattle
Waiting in the wings are a diverse bunch including guinea pigs, domestic
cats and a motley crew of parasites and moulds (see 'Decoders target 18 new
genomes').
The chimpanzee consortium assembled its sequence using the now de rigeur
method of whole-genome shotgun sequencing. This involves cutting up the entire
sequence, some 3 billion letters of code in the chimp's case as in the human
genome, sequencing each section, and reassembling the jigsaw by computer.
The process has got cheaper and easier since the human genome was unveiled
in 2001, after more than a decade of struggle costing hundreds of millions
of dollars. The chimp genome cost no more than an estimated US$50 million.
Some 98% of the data came from blood samples from a single common
chimpanzee, called Clint, who lived at the Yerkes National Primate Research
Center in Atlanta, Georgia. Clint died after a heart failure in January this
year at the tender age of 24; most chimps live into their 50s.
Home truths
So what does Clint's DNA actually tell us? For a start, humans and chimps
are not quite the close cousins we thought. Crude past comparisons of our
DNA showed that our sequences were between 98.5% and 99% identical. That is
indeed the case when considering single-letter differences in the DNA code, of
which there are 35 million, adding up to about 1.2% of the total sequence.
But there are other differences, Eichler says. The two sequences are
littered with duplicated segments that are scattered in different ways in
the two species, he reports in a separate analysis2. These regions add another
2.7% of difference to the tally. "So the 1.2% figure is woefully inaccurate,
" says Eichler.
Much of the difference is seen in genes involved in the immune system. The
contrast suggests that humans and chimps came up against different diseases
during our evolutionary upbringing, Eichler explains.
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The most fertile grounds for human gene duplications are regions near the ends
of chromosomes called subtelomeres, reports a team led by Barbara Trask of the
Fred Hutchinson Cancer Research Center in Seattle3. These areas are still
poorly understood, she says, and could tell us more about our own evolution.
But in terms of what makes us human, the most exciting areas of our genome are
six regions, containing a few hundred genes, that show very little variation
from human to human, but more variation in chimps. This implies they were
important in our evolution. Enticingly, says Eichler, one of these regions
is home to a gene called FOXP2, which is crucial for producing coherent
speech.
Could this be the thing that really sets us apart from other apes? Eichler
warns against getting too excited just yet. "I'm a bit pessimistic that this
is the silver bullet," he says. "But it's a part of it."
References
1. Chimpanzee Sequencing and Analysis Consortium Nature, 437. 69 - 87 (
2005).
2. Cheng Z., et al. Nature, 437. 88 - 93 (2005). | Article | PubMed |
3. Linardopoulou E. V., et al. Nature, 437. 94 - 100 (2005). | Article |
PubMed |
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