Roughly six years ago, David Page's lab at Whitehead Institute for Biomedical Research reported the discovery of eight large areas of mirror-imaged genetic sequences, or palindromes, along the Y chromosome.
Because the Y chromosome essentially has no partner with which to swap genes, a process that between ordinary chromosome pairs leads to genetic diversity and the exchange of good genes for damaged ones, it relies on its own palindromes to swap genes with itself. The Y, as it turns out, folds itself in the middle of palindromic regions, thereby pairing identical sequences to allow for potentially beneficial genetic exchange.
At the time, the finding provided explanation for why, despite much-heralded reports to the contrary, the Y chromosome is not doomed to extinction. Now, the Page lab has discovered that the Y's process of self-preservation can randomly go awry, with considerable clinical consequence.
"We began to think seriously about the centromeres and the activity around them. Two centromeres render the chromosome susceptible to damage," says Julian Lange, first author of the Cell paper and a former graduate student in the Page lab. Because of the Y chromosome's well known roles in sex determination and male fertility, Lange began to speculate about the potential clinical impact of the transmission of an idicY during fertilization.
"Because the Y chromosome is not essential to an individual's survival, these isodicentric Ys can persist," says Lange, who, after completing this research at Whitehead, became a postdoctoral fellow at Memorial Sloan-Kettering Cancer Center. "They can be found in the population."
"We had predicted this correlation, which relates to the overall distance between the centromeres," says Page. "But when we confirmed it with the patient data, we were blown away."
Page believes that this new model for the formation of idicY chromosomes, coupled with the size-instability correlation, suggests a causal link to Turner syndrome, a chromosomal abnormality in girls or women, characterized by the lack of one sex chromosome. Turner syndrome affects an estimated 1 in 2500 females. Page won't yet speculate as to what percentage of Turner syndrome could be caused by this palindrome-to-palindrome recombination, but he does think it's significant.
Written by Matt Fearer
David Page's primary affiliation is with Whitehead Institute for Biomedical Research, where his laboratory is located and all his research is conducted. He is also a Howard Hughes Medical Institute investigator and a professor of biology at Massachusetts Institute of Technology.
"Isodicentric Y Chromosomes and Sex Disorders as Byproducts of Homologous Recombination that Maintains Palindromes"
Cell, September 4, 2009
Julian Lange (1), Helen Skaletsky (1), Saskia K.M. van Daalen (2), Stephanie L. Embry (3), Cindy M. Korver (2), Laura G. Brown (1), Robert D. Oates (4), Sherman Silber (5), Sjoerd Repping (2), and David C. Page (1).
1. Howard Hughes Medical Institute, Whitehead Institute, and Department of Biology, Massachusetts Institute of Technology, 9 Cambridge Center, Cambridge, MA 02142, USA
2. Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Academic Medical Center, University of Amsterdam, the Netherlands
3. Institute for Genome Sciences and Policy, Duke University, Durham, NC 27708, USA
4. Department of Urology, Boston University Medical Center, Boston, MA 02118, USA
5. Infertility Center of St. Louis, St. Luke's Hospital, St. Louis, MO 63107, USA
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