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The Spawning of a New Lifeform
Evolution skeptics sometimes pose mocking questions like, "When has a dog ever produced something that is not a dog?" The foundation of such a question is flawed, but amazingly we can now say that such a thing has happened!
A few days ago Carl Zimmer highlighted a paper that just came out in Cell. Canine transmissible venereal tumor (CTVT) in an infectious tumor that is spread in dogs by sexual contact, as well as biting and sniffing. It has been known for years that infectious viruses can cause tumors, but that is not the case here. The agents of CTVT transmission are the tumor cells themselves. When scientists looked at tumor DNA, they found that it did not match that of host dogs. Furthermore, all of the tumors examined were closely related genetically. The scientists estimate that the tumor arose in wolves or east Asian dogs somewhere between 200 and 2500 years ago.
So essentially this dog tumor seems to have become its own parasitic lifeform. That's way cool if you ask me!
Abstract:
The transmissible agent causing canine transmissible venereal tumor (CTVT) is thought to be the tumor cell itself. To test this hypothesis, we analyzed genetic markers including major histocompatibility (MHC) genes, microsatellites, and mitochondrial DNA (mtDNA) in naturally occurring tumors and matched blood samples. In each case, the tumor is genetically distinct from its host. Moreover, tumors collected from 40 dogs in 5 continents are derived from a single neoplastic clone that has diverged into two subclades. Phylogenetic analyses indicate that CTVT most likely originated from a wolf or an East Asian breed of dog between 200 and 2500 years ago. Although CTVT is highly aneuploid, it has a remarkably stable genotype. During progressive growth, CTVT downmodulates MHC antigen expression. Our findings have implications for understanding genome instability in cancer, natural transplantation of allografts, and the capacity of a somatic cell to evolve into a transmissible parasite.(FYI, the tumor is derived from histiocytes, which as far as I can tell is just another name for macrophages.)
4 comments:
Don't forget the Tasmanian Devils who are spreading a cancer cell line by biting one another's faces.
I still don't see the case for macro-evolution here. The silly dog is still producing -dogs!
BTW,
Since when is a tumor or cancer cell cosidered an "animal"? Last time I checked, those were not included in the animal kingdom, so the dogs have definately not given birth to a new "species".
John,
Thanks for bring the Tasmanian Devils up. Carl Zimmer discussed those so I didn't mention them.
Rob,
My introduction was a little tongue-in-cheek. As to whether this thing should be its own species--well I guess we're entering into one of those fuzzy areas of biology where rigid classification schemes have trouble.
BTW, are you saying that animals gave birth to something that is not an animal? :)
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