OMIA:001199-30640 : Coat colour, extension in Sciurus carolinensis (gray squirrel)

In other species: lorises , coyote , dog , red fox , American black bear , domestic cat , jaguar , ass (donkey) , horse , Przewalski's horse , pig , Arabian camel , reindeer , taurine cattle , indicine cattle (zebu) , goat , sheep , rabbit , Mongolian gerbil , domestic guinea pig , domestic yak , fallow deer , alpaca , raccoon dog , antarctic fur seal , woolly mammoth , rock pocket mouse , oldfield mouse , lesser earless lizard , Geoffroy's cat , jaguarundi , Colocolo , little striped whiptail , water buffalo , Arctic fox

Categories: Pigmentation phene

Links to possible relevant human trait(s) and/or gene(s) in OMIM: 266300 (trait) , 155555 (gene)

Mendelian trait/disorder: yes

Considered a defect: no

Key variant known: yes

Year key variant first reported: 2009

Cross-species summary: The extension locus encodes the melanocyte-stimulating hormone receptor (MSHR; now known as MC1R). This receptor controls the level of tyrosinase within melanocytes. Tyrosinase is the limiting enzyme involved in synthesis of melanins: high levels of tyrosinase result in the production of eumelanin (dark colour, e.g. brown or black), while low levels result in the production of phaeomelanin (light colour, e.g. red or yellow). When melanocyte-stimulating hormone (MSH) binds to its receptor, the level of tyrosinase is increased, leading to production of eumelanin. The wild-type allele at the extension locus corresponds to a functional MSHR, and hence to dark pigmentation in the presence of MSH. As explained by Schneider et al. (PLoS Genet 10(2): e1004892; 2015), "The most common causes of melanism (black coat) mutations are gain-of-function alterations in MC1R, or loss-of function alterations in ASIP, which encodes Agouti signaling protein, a paracrine signaling molecule that inhibits MC1R signaling". Mutations in MC1R have been associated with white colouring in several species.

History: McRobie et al. (2014) showed that the same 24bp deletion occurs in North American gray squirrels as in British gray squirrels. Noting that the British gray squirrel arose from importations from the North American squirrel in the late 19th century, the authors concluded that "the melanic gray squirrel found in the British Isles originated from one or more introductions of melanic gray squirrels from North America".

Molecular basis: By sequencing an obvious candidate gene in three coat-colour phenotypes (the wild-type gray, a jet-black, and a brown–black phenotype) of the British gray squirrel, McRobie et al. (2009) identified a causal mutation in MC1R: "The gray phenotype was homozygous for the wild-type allele E^+, the jet-black phenotype was homozygous for the MC1R-Δ24 allele E^B ["at amino acid positions 87–94"], and the brown–black phenotype was heterozygous for the E^+ and E^B alleles." McRobie et al. (2014; FEBS Lett) showed "that agouti signalling protein (ASIP) is an inverse agonist to the MC1R-wt but is an agonist to the MC1RΔ24. We conclude that the deletion in the MC1RΔ24 leads to a receptor with a high basal activity which is further activated by ASIP. This is the first report of ASIP acting as an agonist to MC1R".

Associated gene:

Symbol Description Species Chr Location OMIA gene details page Other Links
MC1R Sciurus carolinensis 16 NC_062228.1 (193097..189916) MC1R Homologene, Ensembl , NCBI gene


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WARNING! Inclusion of a variant in this table does not automatically mean that it should be used for DNA testing. Anyone contemplating the use of any of these variants for DNA testing should examine critically the relevant evidence (especially in breeds other than the breed in which the variant was first described). If it is decided to proceed, the location and orientation of the variant sequence should be checked very carefully.

Since October 2021, OMIA includes a semiautomated lift-over pipeline to facilitate updates of genomic positions to a recent reference genome position. These changes to genomic positions are not always reflected in the ‘acknowledgements’ or ‘verbal description’ fields in this table.

OMIA Variant ID Breed(s) Variant Phenotype Gene Allele Type of Variant Source of Genetic Variant Reference Sequence Chr. g. or m. c. or n. p. Verbal Description EVA ID Year Published PubMed ID(s) Acknowledgements
674 Melanism (black) MC1R E^B deletion, gross (>20) Naturally occurring variant MC1RΔ24 allele E^B ["at amino acid positions 87-94"] 2009 19643815

Cite this entry

Nicholas, F. W., Tammen, I., & Sydney Informatics Hub. (2014). OMIA:001199-30640: Online Mendelian Inheritance in Animals (OMIA) [dataset].


Note: the references are listed in reverse chronological order (from the most recent year to the earliest year), and alphabetically by first author within a year.

2014 McRobie, H.R., King, L.M., Fanutti, C., Symmons, M.F., Coussons, P.J. :
Agouti signalling protein is an inverse agonist to the wildtype and agonist to the melanic variant of the melanocortin-1 receptor in the grey squirrel (Sciurus carolinensis). FEBS Lett 588:2335-43, 2014. Pubmed reference: 24879893. DOI: 10.1016/j.febslet.2014.05.032.
McRobie, H.R., King, L.M., Fanutti, C., Coussons, P.J., Moncrief, N.D., Thomas, A.P. :
Melanocortin 1 Receptor (MC1R) Gene Sequence Variation and Melanism in the Gray (Sciurus carolinensis), Fox (Sciurus niger), and Red (Sciurus vulgaris) Squirrel. J Hered , 2014. Pubmed reference: 24534267. DOI: 10.1093/jhered/esu006.
2009 McRobie, H., Thomas, A., Kelly, J. :
The genetic basis of melanism in the gray squirrel (Sciurus carolinensis). J Hered 100:709-14, 2009. Pubmed reference: 19643815. DOI: 10.1093/jhered/esp059.

Edit History

  • Created by Frank Nicholas on 18 Jul 2010
  • Changed by Frank Nicholas on 12 Oct 2011
  • Changed by Frank Nicholas on 12 Dec 2011
  • Changed by Frank Nicholas on 21 Mar 2012
  • Changed by Frank Nicholas on 26 Feb 2014
  • Changed by Frank Nicholas on 03 Oct 2014