Research news
Making sense of centromeres
Pete Moore

Journal of Biology 2004, 3:16

The electronic version of this article is the complete one and can be found
online at: http://jbiol.com/content/3/4/16

      Published   31 August 2004

© 2004 BioMed Central Ltd
Comparative analysis of the proteins that bind exclusively at the centromere
provides evidence of an evolutionary battle that may make sense of sex.

At the pinched waist of each eukaryotic chromosome is a region that is both
elusive and enigmatic. Despite considerable effort, and multiple
announcements of completed genome sequences, this zone stubbornly refuses to
reveal its complete sequence, and what little we know of it at first sight
runs counter to standard theories of evolution. The region in question is,
of course, the centromere.

Back in the 1880s, scientists worked out that centromeres played a critical
part in helping cells get their fair share of chromosomes during cell
division, and we now know that it is at these sites that spindle
microtubules attach. "It's not just another intriguing organelle that we
would like to understand; it is central to eukaryotic biology," claims
Steven Henikoff, researcher in the Basic Sciences Division of the Fred
Hutchinson Cancer Research Center, Seattle, and senior author of the study
of centromere protein evolution published in Journal of Biology [1] (see the
'The bottom line' box for a summary of the work). In prokaryotes, chromosome
segregation at division occurs simultaneously with DNA replication, whereas
in eukaryotes the two processes occur at different points in a complex cell
cycle. And while the rest of the chromosome's DNA is packaged away and
consequently 'silenced' during mitosis, the centromere alone remains active
in directing chromosomal movement. "The centromere is unique in eukaryotic
biology - there is nothing else like it - and when we look at its evolution
we find that there is nothing like it either," says Henikoff.

While the exact detail of the DNA sequence at the centromeres (see the
'Background' box) is unknown, it is clear that the DNA is highly variable at
this region both in sequence and in amount - so much so that
centromere-specific DNA in the human Y chromosome varies in size by one
order of magnitude between people, a feature that is also sometimes seen in
other chromosomes. "The paradox is that normal expectations of evolutionary
biology say that a region with such a critical and highly conserved function
should have a stable sequence," says Kevin Sullivan, in the Department of
Cell Biology at The Scripps Research Institute, who has been working on the
structure and function of centromere proteins for 15 years. One would expect
the DNA sequence to be passed on almost unchanged from individual to
individual and even from species to species. But in reality, flies, yeast,
plants and mammals have highly individualistic versions of centromere DNA

Full Text at Journal of Biology
http://jbiol.com/content/3/4/16

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