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April 11, 2014

Starfish Secrets: Did Echinoderms Cure Cancer?




Since my theory does say that all Bilaterians accumulated defenses against cancer is it possible that other animals have defenses that might be adaptable to treating or preventing human cancers? Interestingly, researchers at the University of Rochester recently identified a chemical in naked mole rats that seems to make them “cancer-proof.” Although Dr. Vera Gorbunova, one of the lead investigators, had access to my book and cited it in some of her earlier papers, I am certain that neither she nor her colleagues needed guidance from me or from  any evolution theorist to prompt their interest in naked mole rats. After all, researchers have established that other rodents not only experience cancer but may be especially susceptible to it: as mentioned on p134 of Cancer Selection two National Cancer Institute investigators [Anderwont and Dunn] found tumors in more than 40 percent of randomly gathered wild mice. Considering the widely known facts about cancer in rodents the Rochester investigators did not need any evolutionist to suggest that it might be worthwhile examining the rare rodent species that seems not to experience any cancer. Nor would they need much thought to suspect that those cancer-free rodents may even have acquired, over evolutionary time, an efficient anti-cancer mechanism.  

However, I think there may be other animals that might warrant investigation as possible possessors of potentially useful cancer defenses: the echinoderms. These Bilaterians (1) exhibit a characteristic which, according to my theory, complex animals ought not to possess: they regenerate damaged parts with spectacular efficiency. In my book (pp 79, 83 and 144) I argue that the reason most Bilaterians (and especially the more complex ones) do not regenerate as routinely and as competently as, for example, Hydra, is that regeneration involves increased production of somatic cells, each possessing cancer-triggering mechanisms embedded in oncogenes. (My theory asserts that only Bilaterians can die of cancer.)  To prevent death from cancer natural selection would have favored strict limits over regeneration despite its obvious survival benefit. Although I did note (on p79) that starfish can regenerate an entire animal complete with internal organs from one amputated arm, I may have underestimated the significance of that fact.   

To give some sense of the echinoderms’ regenerative powers, consider this quotation from the abstract of University of Milan’s Dr. Candia Carnevali’s 2006 paper Regeneration in Echinoderms: repair, regrowth, cloning.

Regenerative potential is expressed to a maximum extent in echinoderms. It is a common phenomenon in all the classes, extensively employed to reconstruct external appendages and internal organs often subjected to amputation, self-induced or traumatic, rapidly followed by complete successful re-growth of the lost parts. Regeneration has been studied in adult individuals as well as in larvae. In armed echinoderms, regeneration of arms is obviously frequent: in many cases, the detached body fragments can undergo phenomena of partial or total regeneration independently of the donor animal, and, in a few cases (asteroids), the individual autotomised arms can even regenerate to produce new complete adults, offering superb examples of cloning strategies.

Aside from the theoretical considerationif I am correct to claim that avoidance of flamboyant regeneration is a cancer defense, does that imply that any Bilaterian exhibiting such activity has solved its cancer problem?(2)what do observable facts say about cancer in echinoderms? Well, a search of Google Scholar shows no reports of echinoderm cancers and Wellings reported unsuccessful efforts to  initiate it artificially: “A number of attempts were made to induce neoplasia in post-embryonic echinoderms by the injection of carcinogenic hydrocarbons, or other substances, but there are no recorded examples of a successful result.”

If modern echinoderms are indeed free of cancer what is the evolutionary explanation? I believe there are two possibilities: they have completely lost the ability to trigger cancer (if they once possessed functional oncogenes those cancer triggers have since been altered to such an extent that cancer cannot even be induced) or they do possess functioning oncogenes but their gene pool discovered, as did that of the naked mole rats, a way to avoid the initiation of detectable cancer.

Notes

1. Although starfish and other echinoderms adapt radial symmetry as adults they are bilaterally symmetrical as larvae and are thus classified as Bilaterians.

2. I also use the logic of my theory to suggest in another posting that the apparent absence of cancer in certain rodents is related to their extraordinary life span: Do Naked Mole Rats Confirm That Senescence is a Cancer Defense?
Do Naked Mole Rats Confirm That Senescence is a Cancer Defense? - See more at: http://cancerselection.blogspot.com/2013/08/do-naked-mole-rats-confirm-that_20.html#sthash.KfZ444k7.dpuf

References

Carneveli, M. D. C. "Regeneration in Echinoderms: repair, regrowth, cloning." Invertebrate Survival Journal 3 (2006): 64-76.

Wellings, S. R. "Neoplasia and primitive vertebrate phylogeny: echinoderms, prevertebrates, and fishes--A review." National Cancer Institute Monograph 31 (1969): 59.

Comments and questions are welcomed here.

At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and  the 1992 Nature review of my book.

Copyright © 2014 by James Graham

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