Key Black Pigment Gene Described by Science

Blanched guppy.

Yesterday I posted this link to facebook: http://www.biomedcentral.com/1756-0500/4/31.

The article is titled, "The MC1R gene in the guppy (Poecilia reticulata): Genotypic and phenotypic polymorphisms" by Ayumi Tezuka et. al at Japanese and UK universities.

I call the article on the identification of the MC1R gene "one small step for science, one large step for the hobby." Why am I so excited?

Please correct me if I am wrong, but this is the first time a color gene in the guppy has actually been identified at the molecular level. In other words, the actual DNA sequence on a physical gene has been identified and linked to its phenotypical appearance. In such scientific papers as those by Dr. O. Winge or Dr. Violet Phang genes have been hypothesized based on genetic analysis but they have not actually been associated with a specific region of DNA on a specific gene. They remain abstract. The researchers in the MC1R paper found the actual sequence of base pairs on a physical gene corresponding to black color in guppies.

The MC1R gene is actually well known in animal pigmentation studies. It is found throughout the animal kingdom. Even humans have an MC1R gene. A variant of that gene produces red hair in people. I am not going to describe the MCR1 gene in depth here as I have done so in my published works, other than to make some general comments. (There are many good introductions to the MC1R gene. See Wikipedia: http://en.wikipedia.org/wiki/Melanocortin_1_receptor. Another good article that places MC1R in the context of animal pigmentation is: http://www.oeb.harvard.edu/faculty/hoekstra/pdfs/hoekstra2006her.pdf).

There is a molecule on the surface of black color cells (melanophores) that provides the communication link between the world outside the cell and the cell's internal production of black pigment. It is called the melanocortin 1 receptor or MC1R. This is what the MC1R genes codes for. Think of it as a switch that turns on the black color cell's black pigment making factory or turns it off. If the gene becomes dysfunctional the signaling function of the melanocortin 1 receptor is affected. Normally hormones act on it to signal the production of more or less pigment. But it can malfunction and turn on permanently causing an overproduction of black. I suspect this is the basis for the Black Moscow.

In order to appreciate why I consider the paper a breakthrough, you need to understand pigment pathways. Again I explain this concept in my books, and you can read about it in the source I have cited above, but essentially what this means is that there is not a single gene that controls the production of black in the guppy, there are quite a number of genes that act in concert. Think of it as a factory production line involving many different stations of assembly and even suppliers of parts from distant sources.

Pigment pathways give you a better conceptual framework for understanding patterns on the guppy. I found the guppy shown in the picture above in a pet shop. It is a half-black guppy, but the black on its peduncle and the reticulation pattern of the body is very pale and weak. I believe this "blanching" of the guppy is due to a failure in the pigment pathway for black color. Instead of assigning the pattern to a single gene, I see the pattern as being the result of the state of a number of different genes and genetics switches. I believe I will be able to show in my new book why a Moscow and a snakeskin are both the end product of different mutations in the pigment pathway for black. This is a very different vision of guppy color than suggested by the work of Winge, Dzwillo or Phang. Would I have discovered the "blanched" guppy in the pet store if I did not have a current frame of reference for black in the guppy? Probably, because it was lighter than its tank mates. But what I actually saw was evidence for a failure in the melanocortin signaling pathway. That was much more exciting and mentally challenging.

Why am I so excited? Here it is 2011 and science has just got around to identifying perhaps the most important player in the color patterns of the guppy. I first began writing about it in the early part of the previous decade and was soundly criticized for what many called my speculative research. But the odds that the guppy had the MC1R gene was extremely high since it has been found in other fish and it was shown to play a major role in the pigmentation of animals throughout the animal kingdom. The fact that it is found in the guppy is unexciting for most scientists because they fully expected to find it. What is exciting is that the scientists involved in the study suspect that the MC1R gene in the guppy may play a key role in its polymorphism, its ability literally to change its spots. This is precisely where I have been looking in the past year or so in my own more speculative research as yet unpublished. (The book I am currently writing has several chapters on it.)

In a previous blog I lamented that the progress I have made in understanding guppy color pattern and inheritance may be lost to future generations of guppy hobbyists. The publication of the article on the MC1R gene completely removes this worry from my mind. Even if my books are lost, somebody else in the hobby will stumble across this pivotal paper at some time in the distant future. If they are able to understand what the scientists in the paper are talking about, they will have arrived at the same point I am at now. Hopefully by then science will have delivered even more solid research on the biological basis for guppy color.

I can say this. If you understand how the melanocortin signaling pathway works, then you have the conceptual framework in place to understand current guppy genetic theory. Do you understand pigment pathways?

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