The siamese rat, a biological view

I just read about the siamese gene c(h) in rats, and it was just interesting, I wanted to let ya know why they dont produce that seal color all over.

The science stuff:
The tyrosinase enzyme converts tyrosine (colorless) into dopaquinone (colorless). Phaeomelanins (red to yellow pigment) are made out of dopaquinone.

A mutation of the tyrosinase enzyme caused by the chinchilla gene creates the albino (CC) and the siamese (c(h)) by making it semi-functional.

The semi-functional tyrosinase is very fragile and temperature dependent. When it is too warm, the tyrosinase breaks, and it will no longer convert tyrosine into dopaquinone, which means no more phaoemelanin (red yellow) pigments. That is why the pigment is only created in cooler extremities of the body. (so why isn't the body black? Because dopaquinone creates the dopachrome to create emelanin (black brown) and the tyrosinane can't be converted to create it by the chinchilla gene)

When you mix the dilute gene into the siamese you get blue point siamese.

(The dilute gene is a mutation that literally stops the pigment from reaching the cell edge, creating the "steel blue" color.)

I don't know if there is any way to really stop the eumelanin from being created in the extremeties. Because a fawn or yellow point rat would be totally cool.

Hope it wasnt to muddled to read!

Very intresting! Where did you get the info from? It sounds well grounded. I would love to study this further if the information is out there to be had.

Thanks.

http://www.ratbehavior.org/CoatColorMutations.htm : its all there. Why does it say this thread was moved??

Just a glitch in the system.

When you quote someone word for word, please put it in quotes and cite the source, otherwise it looks as if you are copying their words as your own, which can become rather confusing and "muddled", not to mention an infringement of copyright.

Cut from Rat Behaivor.org, bottom of screen, the Chinchilla gene :

Quote:

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The chinchilla gene has other known mutations, however, and many of them result in a semi-functional tyrosinase. These produce animals with diluted color compared to those with normal tyrosinase. In the acromelanic version, the semi-functional tyrosinase is very fragile and temperature dependent. Raise the temperature too much and the tyrosinase breaks. Rats and other animals with temperature-sensitive tyrosinase only produce pigment in the cooler areas of their bodies: the extremeties such as nose, ears, feet and tail. Animals with these temperature-sensitive mutations are siamese or himalayan. For a specific molecular description of how the tyrosinase produced by the achromelanic mutation differs from the normal tyrosinase, see Kwon et al. 1989.

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http://www.ratbehavior.org/CoatColorMutations.htm

I had heard that before (makes sense since only the cold body parts are dark.. and the cooler the room temp is where you keep them the darker they get.)

I'm going to check out that site to see what else they have there.. I'm very interested in this sort of thing.

Now when I first read about the chinchilla gene on AFRMA, the ladie that wrote it explained that the Phaeomelanins were completely cancelled out by the c(h) gene. But that's not the case with this explanation. She said it would be impossible to create a flame point rat (like the cat) because of this. I'll have to read on it more, but that doesn't seem to be the case with this explanation. I've been thinking on different ways to get the eumelanins diluted or stopped to create the flame point. I think it would be a very cool project to dinker with.
I would also like to point out that the first post wasn't copied word for word. (I put the original text in that last post) :)

I am really glad that you posted this! It clears up- alot for me that I had been wondering. So I guess it'd be similar with Siamese and Himilayan cats too?

littleindiangirl - you might want to change the link in your signature from www.hawthorn.org.uk to www.hawthorn.org.uk/varieties.asp - glad you like the site though :)

I have bred both red eye dilute point Siamese (chch rr) and pink eye dilute seal point Siamese (chch pp) ... both are white rats with pale eyes. Not really projects worth continuing with, unfortunately.

I wonder about the fawn gene on a blue point siamese? Has that been bred?
I wonder why the pigments failed to produce at all when that second dilute was introduced. Was the tyrosinase too fragile, and made completely unfunctional with the second dilute? I guess I will have to differentiate between the functions of the pp and rr gene's compared to the dilute dd gene. Very interesting!

[edit] another thought also, does being agouti with the c(h) rr make any difference? You didnt really specify. I think if it were a self, the beige/buff would then be completely cancelled out. I'm just mowing over why it didnt work.

Oh btw, does the link not work for you? I get automatically fowarded when I click on it.

Quote:

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Originally Posted by littleindiangirl

I wonder about the fawn gene on a blue point siamese? Has that been bred?

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I can't think of anyone who has bred one off the top of my head, but it wouldn't be any different to a non-dilute RED Siamese. All the dilute gene would do is further dilute the pigment, which is already paled out to white ...

Quote:

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Originally Posted by littleindiangirl

I wonder why the pigments failed to produce at all when that second dilute was introduced. Was the tyrosinase too fragile, and made completely unfunctional with the second dilute? I guess I will have to differentiate between the functions of the pp and rr gene's compared to the dilute dd gene. Very interesting!

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I think a lot of it is just the fact that the pigment colour in rr and pp rats is so pale that it's just not possible to see on a Siamese rat. Consider that even black can only express itself to a dark brown seal colour, and you can see how hard it would be for the extremely deformed melanin in a PED or RED rat to express itself at all when restricted by the Himalayan gene. The eyes on a RED Siamese will be darker than the eyes on a PED Siamese though.

Quote:

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Originally Posted by littleindiangirl

[edit] another thought also, does being agouti with the c(h) rr make any difference? You didnt really specify. I think if it were a self, the beige/buff would then be completely cancelled out. I'm just mowing over why it didnt work.

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From the limited breeding I did, it doesn't appear to make a difference if the rats are agouti or non-agouti based with Siamese. You might see a small amount of agouti banding on a really nice agouti point, but once you add the dilutes in it's impossible to see.

I thought the link didn't work ... but then I remembered I did add a forwarding page earlier. I will probably put some sort of main site back on the domain, leaving the varieties/genetics at the varieties.asp link in the future though.

It must just be too fragile then. That has to be it. I'm just confused why the blue comes through so well, but any other dilutes just pale it out so much. That bites, I would have liked to see a nice topaz/fawn point.
Thanks for all the great information! I do really love the site, I go there quite often, its such a great listing. ;)

You know what else I just thought of, the brown mutation. Its a very warm color when agouti, not quite chocolate, not quite cinnamon. That sound plausible at all? LOL, tell me when to stop, I'm just overly excited when I think of new ways to get around the complete dilution.

Not sure what relevance brown has here? Adding more colour modifying genes will only ever make the rat lighter, not darker...