Molecularbiology
The Receptor called MC1R (see graphic) is causing the pigment type switching.
- If the receptor signals, dark eumelanin is produced.
- If there is no signal, light pheomelanin is produced.
- Normally the ubiquitous MSH (blue square in the graphic, melanocyte stimulating hormone) is connected to the receptor causing signaling -> dark pigment
- spatial/temporal ASIP (green triangle, Agouti signal protein) is produced, which has a stronger binding ability, so it replaces MSH and binds to the receptor, preventing signaling -> light pigment
- e produces a receptor with 10 missing proteins rendering it (at least partly) nonfunctional.
- ED produces a receptor with 2 missing proteins rendering it (over)active
- eJ produces a receptor with 1 substituted and 2 missing proteins rendering it (over)active and only working in some parts of the skin (this differentiation occurs in early development and is inherited on proliferation). The mutation is on a similar place of the adjacent transdomain part of MC1R.
- Messenger RNA (needed to build receptors) was found in dark hair skin regions only. A composite six bp in-frame deletion in the melanocortin 1 receptor (MC1R) gene is associated with the Japanese brindling coat colour in rabbits (Oryctolagus cuniculus) - BMC Genomic Data
Very helpful summary of the receptor basis of the coloration, thank you! I especially liked the description of the action of <ej>.
The summary is concise enough for me to ask some questions.
For instance, where does <Es> fit into this scheme? Is there similar information about <Es> regarding its protein deletions or substitutions?
ED
They wrote it may be ED or ES. They found one mutation and dont know which one it is. But if you look at the rabbits which are found to carry the mutation in this and other Fontanesi papers, yo will find them all self colored (californian, black/blue checkered giant, white giant, new zealand white, black/blue dutch), there is no one probed which actually shows ES, so yes one could not know...
I provided samples from ESE rabbits, but i think unfortunately they are still not yet fully sequenced.
I know from one ES sample, where the same mutation as in the black rabbits was found, but this sequencing only includes the DNA part where this mutation resides. The rest of the receptor DNA was not sequenced. So you could guess it may be the same, but it could be as well as with f.e. himi and chinchilla.
Himi occured first and chinchilla later. Both have the same mutation, but chinchilla has an additional one causing the chinchilla coloration.
Tyrosinase gene variants in different rabbit strains - PubMed
From
Robinson, Genetic studies of the rabbit (1958) citing Punnet:
ED appeared earlier, ES later.
I believe I understand that your argument lies not only with the E series, but rather an <Ed> possibly hiding an <A_>. But I cannot reconcile an <A_ Ed_> genotype with the ancestry I know and the offspring I see in my rabbits.
I am as reasonably sure as possible (given my never say never rule
) that I know which rabbits are agouti, and I have no reason to believe that <Ed> gene factors into my line at all. I've never, in 15 years of breeding these particular Satins, had an unexpected agouti show up, other than the chinchillas from the self squirrel x NZW cross, which was explained satisfactorily and backed up by all subsequent breedings. All of my self chins and self squirrels produce exactly what they "should" given their agouti status, when bred to either another self, a tan <at> or another agouti. My <at a> otters, even from the Moon line which carries <Es>, produce exactly what they "should" when bred to a self or to an agouti...except for the bunny with the gold haze, of course, which
could be the exception that proves your argument. (Unfortunately for this discussion, I did not keep that rabbit and cannot use it for test breeding.)
If I understand correctly, you suspect that the self black dam of the bunny with the gold haze might be <Ed> rather than <Es>. But I can't understand why <Ed> would have hidden for so long with so many opportunities for it to show up, or where it would have come from, given its presumed distribution in the U.S. rabbit population.
Also - if the dam was <Ed>, I still don't understand why pairing her with an agouti buck would produce a <A_ Es> kit that looked like that gold-hazed kit. It should look like a GTS, yes? What do you think the genotype of the gold haze kit is? Is that what <A_ Ed_> would look like? I thought <Ed> individuals were completely black. I am more and more mystified by this animal.
Isn't there a US breed with blue, red and white color which brings this colors only (maybe also black?), but no agouti? This could fairly good be caused by ED.
I think you might be referring to the Rhinelander. Given its breed development using both the Harlequin <A_ ej_> and the Checkered Giant (possibly <aa Ed_>), it surely seems possible (and might be a sensible approach) that some Rhinelander individuals are of an <Ed> genotype. Although, the U.S. Rhinelander breed club makes no mention of solid black sports, but only charlies and solid-colored brindled rabbits of brown and orange. Curiously, black is not mentioned in this context. See
History of the Rhinelander – Rhinelander Rabbit Club of America
I cannot really imagine any reason whatsoever to cross either of those giant breeds into a line of purebred Satins, while acknowledging that people do some strange things anyway!
I still have the gold-hazed bunny's dam; in fact she is one of my top producers. According to her pedigree and her offsping, I deduce that she's <aaBBCchDDEsE>. She's been bred with the following bucks:
- self-based, dilute REW <aaB_ccddE_> = self blacks, himis (2 litters)
- blue otter heterozygous for self <ataBBCCddE_> = self blacks, black otters, black himis, martenized black himis (2 litters)
- agouti-based REW <AaB_ccddEe> = self blacks, GTS, himis, and "gold haze" (1 litter)
The bucks' genotypes are also derived using both their pedigrees and their offspring with various does.
UPDATE: I communicated with the president of the Rhinelander Rabbit Club of America and she reports:
"No we do not get solid blacks, our sports are black and orange or blue and fawn with little to no white. Occasionally we get one that appears solid black, but there is always some orange mixed in. Occasionally we get some that would be considered showable as a harlequin."
So it doesn't sound like <Ed> is a factor in the Rhinelanders here anyway.
