MSNBC Chimp genome compared

[Guest guest]

>Chimp genome compared

>A wide-ranging analysis of the chimpanzee genome

>sheds new light on how humans evolved, and could

>eventually result in new medical therapies as

>well.

>http://www.msnbc.msn.com/id/9136200/

 

Chimp genetic code opens human frontiers

Genome comparison reveals many similarities - and crucial differences

By Alan Boyle

Science editor

MSNBC

Updated: 3:27 p.m. ET Aug. 31, 2005

 

 

Scientists unleashed a torrent of studies

comparing the genetic coding for humans and

chimpanzees on Wednesday, reporting that 96

percent of our DNA sequences are identical. Even

more intriguingly, the other 4 percent appears to

contain clues to how we became different from our

closest relatives in the animal kingdom, they

said.

 

" We're really looking at an individual

evolutionary event, and this is spectacular, "

said University of Washington geneticist Robert

Waterston, senior author of a study in the

journal Nature presenting the draft of the

chimpanzee genome.

 

The achievement should lead to discoveries with

implications for human health, including new

approaches to treating age-old diseases, said

Francis Collins, director of the National Human

Genome Research Institute.

 

" As we build upon the foundation laid by the

Human Genome Project, it's become clear that

comparing the human genome with the genomes of

other organisms is an enormously powerful tool

for understanding our own biology, " he said in a

written statement.

 

The chimpanzee genetic blueprint is the result of

a multimillion-dollar effort involving 67

researchers from the United States, Israel,

Italy, Germany and Spain. In addition to that

blueprint, more than a dozen other related

reports are being published this week in Nature

and two other scientific journals, Science and

Genome Research.

 

Among the highlights from the analyses:

Small but crucial differences: The researchers

said the results confirmed the common

evolutionary origin of humans and chimpanzees.

Out of the 3 billion base pairs in the DNA coding

for chimps and humans, about 35 million show

single-base differences, and another 5 million

DNA sites are different because of insertions or

deletions of genetic code. Waterston estimated

that 1 million of those coding changes are

responsible for the functional differences

between humans and chimps - thus defining our

humanness.

Six new genetic frontiers: Scientists identified

six regions of our DNA that appear to have

evolved dramatically over the past 250,000 years

- including a " gene desert " that may play a role

in nervous system development and also has been

linked to obesity. They said a seventh region

that showed notable change contains the FOXP2

gene, which already has been linked to speech in

humans.

Brain genes key: A comparison of gene expression

in various tissues indicated that most of the

genetic changes occurring during the evolution of

chimps and humans had neither a positive nor a

negative effect. However, the testes in the males

of both species showed strong evidence of a

positive effect. Also, genes active in the brain

showed much more accumulated change in humans

than in chimps - suggesting that those genes

played a special role in human evolution.

Primates' risky business: Scientists compared the

chimp and human genomes with those of mice and

rats, and found that both primates carried a

greater amount of potentially harmful genetic

coding. They speculated that such coding may have

made primates more prone to genetic diseases, but

also more adaptable to environmental changes.

Clues to diseases: The genomes contained hints

that the chimpanzee genetic code has been

attacked more frequently than humans by

retroviral elements - such as those present in

the HIV virus. Scientists also noted key

differences between the genomes that may affect

susceptibility to viruses, the workings of the

immune system and the progression of diabetes and

Alzheimer's disease in humans.

 

The researchers emphasized that the studies

raised more questions than answers, and that it

would take years to decipher the meaning behind

differences in genetic coding.

 

For example, although six new regions of rapid

evolutionary change have been identified, " we

don't know what natural selection in these

regions acted upon, " said Tarjei Mikkelsen, a

graduate student at the Massachusetts Institute

of Technology who was the first listed author for

the chimp genome study.

 

But Waterston said the " really big picture " is

that geneticists can now focus on the small

percentage of DNA coding that is peculiar to

humans, and figure out how that coding works.

 

" We're probably down to a million or so changes

in the human genome that are even candidates for

being the changes that have made us human, " he

told MSNBC.com. " So it's fun and exciting to be

looking at nature's lab notebook like this. "

 

How the job was done

The chimpanzee genome is only the fourth

mammalian genetic sequence to be deciphered,

following up on humans, mice and rats.

 

The DNA used to create the sequence came from the

blood of a male chimpanzee named Clint at the

Yerkes National Primate Center in Atlanta. Clint

died last year from heart failure, at the

relatively young age of 24, but two of his cell

lines have been preserved for medical research.

 

Clint's genetic coding was analyzed using the

same type of " whole-genome shotgun " approach that

produced drafts of the human genome beginning in

2001. Most of the work of sequencing and

assembling the chimp genome was done at the Broad

Institute of MIT and Harvard, and at the

Washington University School of Medicine in St.

Louis.

 

As expected, of the coding that was common to

both human and chimp genomes, 99 percent was

identical. Researchers found that an additional

1.5 percent of the human DNA coding was not found

in chimps, and 1.5 percent of the chimp coding

was missing in humans - bringing the total

difference between the two genomes to 4 percent.

 

In comparison, the genetic codes of two typical

humans are only 0.1 percent different. On the

other hand, the difference is 10 percent for mice

vs. rats, and 60 percent for humans vs. mice.

 

Darwin's claim confirmed

Researchers said the chimp/human comparison

served as the most dramatic confirmation yet of

Charles Darwin's claim in 1871 that humans and

chimpanzees had a common ancestor. Today,

scientists believe that the most recent common

ancestor lived 6 million years ago.

 

" I couldn't imagine Darwin hoping for a stronger

confirmation of his ideas than when we see the

comparison of the human and chimpanzee genome, "

Waterston told reporters during a Washington news

conference.

 

The researchers also used the chimp genome as a

new reference point for judging how rapidly

various areas of genetic code have changed:

Waterston said it appeared that genes linked to

the wiring of the nervous system and the

perception of sound changed particularly quickly

in primates, compared with other mammals.

 

As for genetic changes that are peculiar to

humans, the " most intriguing " one involves

transcription factors, the proteins responsible

for controlling the expression of other genes,

Waterston said. Scientists believe that tweaks in

transcription factors may spark rapid

evolutionary change, even though the genes they

control are relatively unchanged - just as the

same classical melody can sound dramatically

different when given a jazz interpretation.

 

How has the brain changed?

A separate study, published by Science, looked at

how genes were expressed in the brain, heart,

liver, kidney and testes of chimpanzees and

humans. That study found that the brain showed

the least differences between species, while the

liver showed the most.

 

Those findings may seem to go against the idea

that brain development was crucial to the

emergence of modern humans, but the senior author

behind that study, Svante Paabo of the Max Planck

Institute for Evolutionary Anthropology in

Germany, told MSNBC.com that the results were in

line with evolutionary theory. He said the coding

for the brain is complex and highly constrained -

meaning that too much change would impair brain

activity - while the coding for a " simple " organ

such as the liver could vary more without having

a negative impact.

 

" However, even given these constraints, we see

that something special have gone on with the

function of the brain in human ancestors, " Paabo

said in an e-mail message, " since if we compare

how much change occurred in human ancestors

versus in chimp ancestors, more change happened

in our ancestors than in the ancestors of the

chimps in genes expressed in the brain. "

 

Paabo is well-known for his study of the FOXP2

gene, the " language gene, " and he said that

further analyses of the chimpanzee genome were

likely to turn up additional genes that are

responsible for characteristics peculiar to

humans.

 

Broader perspectives

For his part, Waterston said the genome analysis

brought a broader perspective to the question of

what makes us so different from chimpanzees.

 

" You have to think about it the other way: Are we

really as different from chimps as we think? And

I think the basic conclusion has to be that we

are not, " he told MSNBC.com. " What we see as

profound differences are actually somewhat

superficial: We walk upright and they don't. We

have less hair and they have more. We have more

complicated brains. These are fine tuning. ...

The challenge will be to figure out what the

critical differences are. "

 

He also said the studies should change the way we

look at chimps as well as the way we look at

humans.

 

" Chimps in the wild have to be a concern, " he

said. " The environment is being degraded and

encroached upon greatly, and chimps are extremely

threatened in the wild. To watch this happen to

something that's so similar to us has to be a

concern. "

© 2005 MSNBC Interactive

 

© 2005 MSNBC.com

 

URL: http://www.msnbc.msn.com/id/9136200/

--