You *can* teach an old dog new tricks

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…Tricks like a dog cancer cell becoming an independent pathogen and spreading through the dog population. Drop everything and go read Carl Zimmer’s post about the recent discovery of a dog cancer cell lineage that has left behind its multicellular ancestry. Rather like HeLa cells, except in the wild without human help. If I thought that “phylum” and “phylum-level bodyplan” were inviolable, unchanging character complexes (which I don’t), this example of a super-phyletic macroevolutionary change, on microevolutionary timescales, would rock my world.

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Interestingly enough, dyed in the wool chance worshippers apply theories of chance even when it means denying things that make perfect sense in light of common descent. Case in point is Nick Matzke’s article on Panda’s Thumb entitled You ... Read More

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Zimmer’s is the most interesting science post in weeks. An amazing case of speciation.

One biologist even suggested that the cells should be consider a new species.

Sure it is. It’s not a dog anymore, is it?

That’s… amazing.

I can’t help but wonder, though (assuming they’re right that this is a pathenogenic cancer line and not just a pathogenic virus with a symptomatic cancer):

So, gee, when random mutation changed the dog genome to enable these cancerous dog cells to survive as an independent parasite that can propagate and survive in hosts other than the one they originated in… was this an “increase” or a “decrease” in “information”?

I’ve been using HeLa cells as an example of possible cross-phylum macroevolution for a while now. Good to know I have even more ammo on the same level!

Importantly, this speciation event must have involved a series of highly specialized adaptations, e.g. to maximize “seeding”, grafting to different tissues, immune evasion (unlike conventional cancer cells, these guys are able to avoid immune responses in genetically very different hosts). “Just a loss of information” this ain’t.

unlike conventional cancer cells, these guys are able to avoid immune responses in genetically very different hosts

Can you elaborate on this? Did somebody go to the bother of testing implanting tumors in foreign hosts at some point or something?

Can you elaborate on this? Did somebody go to the bother of testing implanting tumors in foreign hosts at some point or something?

Absolutely - people have long experimented with tumor grafting in experimental animals. In particular, certain strains of mice (inbred strains), in which long-term sequential brother-sister mating has led to all individuals being virtually genetically identical, are commonly used for these purposes. Transformed tumor cell lines from one strain may grow in hosts from the same strain, but not in hosts from other, genetically different strains. (And there are some severely immunodeficient mouse strains in which even some human cancers can grow.)

Uh, I guess I’m dumb, but I couldn’t see what makes this different from a cancer-causing virus. Is it just because of the difference in the genetic markers? This makes it a new species? I guess someone will shell out for the full genome analysis then, since it would be such a huge evolutionary discovery?

Recall that bacterial flagella help bacteria hold on to human cells and cause diarrhea, which is still a leading cause of infant death in the third world.

Now the full truth is out: the Designer hates kids and dogs.

Never mind, I see. The genetic markers tell them that the cancer cells are not from the host dog, but are the immortal cells of a long dead dog. Got it.

Now the full truth is out: the Designer hates kids and dogs.

So W.C. Fields is in fact God.

I always suspected.

If I thought that “phylum” and “phylum-level bodyplan” were inviolable, unchanging character complexes (which I don’t), this example of a super-phyletic macroevolutionary change, on microevolutionary timescales, would rock my world.

Which body plan? Sacculina has several.

steve s asks:

It’s not a dog anymore, is it?

Dog + blob of cells = doob

Blob of cells + dog = blog

Delta Pi Gamma (Scientia et Fermentum)

Jason asked:

… I couldn’t see what makes this different from a cancer-causing virus. Is it just because of the difference in the genetic markers?

I think the difference is, unless I’ve read it wrong, that there is no virus.

This makes it a new species?

Yes. A virus might cause cancer by hijacking a cell’s reproductive tools, and then spread and do the same to a new host. But this is the cancer itself “learning” to spread and live in a new host. It shouldn’t happen easily, the immune system is supposed to reject, in general, transplanted cells. This cancer has foiled that transplant rejection.

I think the difference is, unless I’ve read it wrong, that there is no virus.

Hmmm …

But skeptics noted that virus-like particles are often found in or around Sticker’s sarcoma. There’s lots of strong evidence that viruses can trigger cancers (such as cervical cancer), possibly as a strategy to spread themselves rapidly. Dogs that were struck with Sticker’s sarcoma could just be acquiring a cancer-causing virus from other dogs.

Could be, but the evidence strongly suggests otherwise.

Yeah, the adult Sacculina has ditched the arthropod body plan and changed into very bizarre parasite.

Now consider Devil Facial Tumor Syndrome. A contagious cancer found in tasmanian devils, thought to be picked up from dogs. DFTS is found on the face, and in most cases eventually grows to interfere with breathing. This resulting in the animal’s suffocation.

The tumor cells have been found to have devil DNA, but not that of the victim per se. In addition, anomalous DNA has been found in those same cells not otherwise found in tasmanian devils.

Since DFTS is apparently descended from Sticker’s Sarcoma it could be we have the first speciation event in a new phylum.

Yeah, the adult Sacculina has ditched the arthropod body plan and changed into very bizarre parasite.

I hope you read my link to Carl Zimmer’s article about parasites; it is far more informative and interesting than the Wikipedia piece.

Oops, I see that the Wikipedia article links to Zimmer’s. Nevermind.

Popper’s ghost wrote:

I think the difference is, unless I’ve read it wrong, that there is no virus.

Hmmm …

But skeptics noted that virus-like particles are often found in or around Sticker’s sarcoma. There’s lots of strong evidence that viruses can trigger cancers (such as cervical cancer), possibly as a strategy to spread themselves rapidly. Dogs that were struck with Sticker’s sarcoma could just be acquiring a cancer-causing virus from other dogs.

Could be, but the evidence strongly suggests otherwise.

Are we supposed to read “virus-like particles” as a virus, or just an alternate possiblity?

I thought the point was that the tumor had a certain dog’s DNA in its cells, and that’s why the article was called “A Dead Dog Lives On (Inside New Dogs).”

They noted that the tumor cells appeared to share a unique genetic marker.

Where does that marker come from? Do cancers usually have unique genetic markers? If so, why make note of it?

Could a virus be injecting the unique marker?

My god. I never thought we’d have a more perfect example of macroevolution than HeLa. This is stunning.

And I don’t even have to feel all that bad for the dogs!

Are we supposed to read “virus-like particles” as a virus, or just an alternate possiblity?

I think we’re supposed to read it as evidence supporting the possibility of the involvement of a virus. As Zimmer wrote,

Dogs that were struck with Sticker’s sarcoma could just be acquiring a cancer-causing virus from other dogs.

“could be” = “possibility”

Could a virus be injecting the unique marker?

As I said, “the evidence strongly suggests otherwise”. Your statement was “there is no virus”. That’s an inference from the fact that this appears to be a self-replicating strain of dogcell, not the result of a diligent search for a virus and failure to find one.

P.S. Norm, if it seems like I’m quibbling, you’re probably right; we don’t have any substantive disagreement. But instead of saying that the difference is that there is no virus, I would have said that the difference is that the tumors reproduce, rather than each independently being caused by a virus. For all we know, the tumors are hosts to some virus, which might explain the virus-like particles, in which case there is a virus, but it’s not relevant.

Do HeLa cells have a “right to life”?

Is it humane to continue to perform experiments on human organisms?

The issues under discussions:

1. The possible contribution of a virus to the origin to the tumor versus the LINE insertion upstream of c-myc. 2. The origin and development of the unique genetic and cell surface markers. 3. The tumor/host immune system interactions.

These issues differentiate this discussion and its approach to the study of this unique cell by raising specific testable hypotheses. This is in contrast to ID claims of testability where they continue to generate negative or untestable hand waving arguments.

Delta Pi Gamma (Scientia et Fermentum)

Proposition: The virus-like particles are expressions of the cancer cells themselves. The coding therefor inserted into the cell by the original virus. Thus what we have is not a virus per se, but a reminder of the virus.

Update. The Wikipedia article on Devil Facial Tumor Disease (DFTD) can be found here. It has links to other articles on the condition.

Note that DFTD has been connected to Stickers Sarcoma

Alan Kellogg wrote:

Proposition: The virus-like particles are expressions of the cancer cells themselves. The coding therefor inserted into the cell by the original virus. Thus what we have is not a virus per se, but a reminder of the virus.

That’s almost exactly what crossed my mind when I read Zimmer’s article.

However, virii tend to use RNA, not DNA, and I was thinking the coding inserted into the cell was a scrap of dog DNA. A virus might, however, have gotten symbiotically usurped like the ancient proto-cells that became the mitochondria of our cells.

But as Popper’s ghost insists on reminding us, that is all still a big IF, a mere freaky possibility that requires more study.

The coding therefor inserted into the cell by the original virus

Is there any evidence of an “original virus” or of insertion? I think that’s a misreading of the article:

All of the tumor cells shared the same genetic marker. A virus-like stretch of DNA, called a LINE-1 element, had been moved to a new location in the genome of all of the tumor cells. None of the non-tumor cells from the dogs had this LINE-1 element in this particular spot.

Also,

The scientists propose that several centuries ago, a histiocyte cell in a dog or a wolf turned cancerous. A mutation may have caused the cell to become abnormal–perhaps that LINE-1 element that marks Sticker’s sarcoma cells today.

No particular reason to think that a virus was involved (I don’t think “a virus-like stretch of DNA” implies that). Viral involvement was the proposition of the skeptics of the view that the tumor “can be transmitted from dog to dog”, not of the proponents of that view (presumably there are now fewer skeptics as a result of the work of Murgia et al.).

OK, just to clarify some points: - there are many different types of viruses (with both DNA and RNA genomes) that are known to be involved in the transformation of normal cells into tumor cells; - It is entirely possible that the original tumor causing CTVT may have been caused by such a virus, and that the CTVT cells still harbor the virus, and maybe even shed viral particles; - There is however little if any conclusive molecular evidence of viral infection of CTVT cells; - Regardless, as pointed out by Popper’s Ghost and others above, the evidence in the Cell paper convincingly shows that the causative, transmissible agent of CTVT today is the cell line itself, not any associated virus.

Nice summary, Andrea. I didn’t actually say that the evidence is convincing, just strongly suggestive, because I’m cautious about being convinced of anything, I haven’t read the paper or anything else relevant other than Zimmer’s post, and I’m not qualified or competent to make conclusive judgments about such things.

interesting!

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This page contains a single entry by Nick Matzke published on August 11, 2006 3:15 PM.

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