From: Joao Magalhaes (joao.magalhaes@fundp.ac.be)
Date: Thu Dec 05 2002 - 14:31:02 MST
Hi!
At 11:20 05-12-2002 -0800, you wrote:
>It's hard to understand how such a relatively small number of genes being
>different can lead to such enormous differences between the two species.
>Longevity seems like only a small part of the picture.
As I've been trying to convince people working on aging, biology is highly
hierarchical. For example, the few proteins controlling gene expression can
regulate entire complex processes--and why not aging too? Check the work by
the controversial Svante Paabo, for instance:
Enard,W., Khaitovich,P., Klose,J., Zollner,S., Heissig,F., Giavalisco,P.,
Nieselt-Struwe,K., Muchmore,E., Varki,A., Ravid,R. et al. (2002) Intra- and
interspecific variation in primate gene expression patterns. Science, 296,
340-343.
Apparently--I read this at ScienceDirect--, humans have the genes that mice
use to build their tail; presumably, the reason why we don't have a tail is
because a few developmental genes are turned off in humans. Now, regarding
aging, the way I see it, aging is programmed into the genes--how else can
we explain the 25-fold difference in rate of aging between mice and
humans?--and a few key regulatory genes control the rate of aging in
mammals. Now, the question is: which genes? I don't know. That's what we
must find out, but my money is on the DNA repair/transcription complex and
the changes in chromatin structure that involve proteins such as the Werner
protein, Ku, the telomeres, etc.
>One thing I'm finding confusing in the articles is just how different
>the genomes are. We used to hear that humans and chimpanzees were
>something like 98% the same. This article from last May,
>http://www.newscientist.com/news/news.jsp?id=ns99992352, says:
I think the confusion is caused because you're actually comparing different
things. For example, according to this latest paper, humans and mice share
99% of genes. That is to say that if humans have 30,000 genes, mice have
29,700 of these genes. Yet nucleotide similarity between mice and humans is
somewhere around 80%. That is to say that if you align all human genes to
mice genes you get an average of 80% positive hits. Now, regarding chimps,
the latest estimates I read point to 95% genomic similarity in terms of
nucleotide similarity. For baboons, it's about 90%. Yet this does not tell
us anything about how many of the 30,000 human genes chimpanzees have.
They're all nucleotide comparisons.
All the best.
Joao Magalhaes (joao.magalhaes@fundp.ac.be)
Website on Aging: http://www.senescence.info
Reason's Triumph: http://www.jpreason.com
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