North Carolina State University researchers have uncovered evidence that evolutionary¹ "breakpoints" on canine²（犬的） chromosomes⁴ are also associated with canine cancer. Mapping these "fragile" regions in dogs may also have implications for the discovery and treatment of human cancers. When new species evolve, they leave genetic⁵ evidence behind in the form of "breakpoint regions." These regions are sites on the genome where chromosomes broke during speciation (when new species of dogs developed). Dr. Matthew Breen, professor of genomics at NC State, and graduate student Shannon Becker looked at the breakpoint regions that occurred when the canid（犬科动物） (dog) species differentiated⁶ during evolution. They compared the genomes of several wild canine species with those of the domestic dog. By overlaying the genomes, they found shared breakpoints among 11 different canid species -- the so-called evolutionary breakpoints.

"The interesting thing about the breakpoint areas in the canid chromosome³ is that they are the same regions that we have shown to be associated with chromosome breaks in spontaneously occurring cancers," Breen says. "It is possible that the re-arrangement of chromosomes that occurred when these species diverged⁷ from（背离） one another created unstable⁸ regions on the chromosome, and that is why these regions are associated with cancer."

The researchers' results appear in Chromosome Research.

"As species evolve, genetic information encoded on chromosomes can be restructured -- resulting in closely related species having differently organized genomes," says Becker. "In some cases, species acquire extra chromosomes, called B chromosomes. We looked at these extra B chromosomes in three canid species and found that they harbor several cancer-associated genes⁹. Our work adds to the growing evidence that there is an association between cancer-associated genomic instability and genomic rearrangement during speciation."

"The presence of clusters of cancer- associated genes on canid B chromosomes suggests that while previously¹⁰ though to be inert¹¹, these chromosomes（染色体） may have played a role in sequestering¹² excess copies of such genes that were generated during speciation," adds Breen. "We now need to determine whether these stored genes are active or inert（惰性的） -- that information could give us new tools in cancer detection and treatment."

The research was funded by the Morris Animal Foundation. The Department of Molecular¹³ Biomedical Sciences is part of NC State's College of Veterinary Medicine.