Colour and plumage

The colour of skin, hair and feathers are highly variable traits in domestic animals. Firstly, man has strived to protect animals from natural predators thus decreasing natural selection and favouring the appearance of phenotypes rarely observed in natural conditions. Secondly, man has often favoured colour mutations rather than wild phenotypes.

Colour is among the strongest criteria for differentiating breeds and has been widely used for breed standardisation.

The mutations responsible for colour can be classified into three categories:

1. Melanocyte differentiation (responsible for white spotting or flecking);
2. Melanin synthesis (mutations that remove colour or modify the balance between black eumelanin and red phaeomelanin);
3. Subcellular packaging of melanins and transfer to keratinocytes (dilution mutations).

Such mutations have been identified for seven genes in domestic animals i.e. chicken, quail and cattle.

As member of the Animal Genetics division network on "colour genes", GABI contributes to the analysis of colour genes in birds (chickens, quail) within the framework of international partnerships (Sweden, United Kingdom, Taiwan). In addition, other studies are being developed in cattle (in partnership with the Limoges university) and rabbits.

Several mutations responsible for colour modifications of the plumage or the skin have been identified in genes of the second group (see above): MC1R (quail), Agouti (cattle; quail); TYR (chicken) and TYRP1 (quail). In the Normande bovine breed, the continuous variation of the amount of dark pattern is determined by the level of methylation of one of the promotors of the Agouti gene. This depends largely on the deregulation associated with the insertion of a LINE element. The identification of the Agouti gene in quail has provided the first proof that this gene is involved in plumage colour and metabolism in birds. The "white recessive" mutation of the TYR gene has been identified and corresponds to a retroviral insertion into an intron.

Several other mutations involve the third group of genes (see above): SLC45A2 (chicken, quail), MLPH (chicken) andBCDO2 (chicken). The SLC45A2 gene presents several mutations (substitution, deletion, splicing), and is associated with the cream-coloured phenotype in horse. In chicken, the MLPH gene carries the same mutation as that in humans,which is responsible for the Griscelli 3 syndrome. The phylogenetic study of the BCDO2 mutation, responsible for the yellow skin in chicken, has revealed for the first time the contribution of the wild species Gallus sonneratii in chicken domestication whereas Gallus gallus was previously considered as the only wild ancestor. An association study of melanin and major genes responsible for feather colour has been published for quail.

In rabbits, we are seeking the mutation causing the Rex phenotype in the Orylag rabbit, responsible for the disappearance of "rough" fur.

Molecular diagnostic tests developed from these results can now be provided to breeders as a contribution to population management, either for traceability or for improved standardisation of products.

> Publications

- Chang C.M., Coville J.L., Coquerelle G., Gourichon D., Oulmouden A., Tixier-Boichard M. 2006. Complete association between a retroviral insertion in the tyrosinase gene and the recessive white mutation in chickens. BMC Genomics, 7: 19.

- Chang C.M., Furet J.P., Coville J.L., Coquerelle G., Gourichon D., Tixier-Boichard M. 2007. Quantitative effects of an intronic retroviral insertion on the transcription of the tyrosinase gene in recessive white chickens. Animal Genetics, 38: 162-167.

- Eriksson J., Larson G., Gunnarsson U., Bed'hom B., Tixier-Boichard M., Strömstedt L., Wright D., Jungerius A., Vereijken A., Randi E., Jensen P., Andersson L. 2008. Identification of the Yellow Skin Gene Reveals a Hybrid Origin of the Domestic Chicken. PLoS Genetics, 4: e1000010.

- Girardot M., Guibert S., Laforet M.P., Gallard Y., Larroque H., Oulmouden A. 2006. The insertion of a full-length Bos Taurus LINE element is responsible for at transcriptional deregulation of the Normande Agouti gene. Pigment Cell Research, 19: 346-355.

- Gunnarsson U., Hellström A.R., Tixier-Boichard M., Minvielle F., Bed'hom B., Ito S., Jensen P., Rattink A., Vereijken A., Andersson L. 2007. Mutations in SLC45A2 Cause Plumage Color Variation in Chicken and Japanese Quail. Genetics, 175: 867-877.

- Hiragaki T., Inoue-Murayama M., Miwa M., Fujiwara A., Mizutani M., Minvielle F., Ito S. 2008. Recessive black is Allelic to the yellow Plumage Locus in Japanese Quail and Associated with a Frameshift Deletion in the ASIP Gene. Genetics, 178: 771-775.

- Minvielle F., Cecchi T., Passamonti P., Gourichon D., Renieri C. 2009. Plumage colour mutations and melanins in the feathers of the Japanese quail: a first comparison. Animal Genetics, 40: 971-974.

- Minvielle F., Gourichon D., Moussu C. 2005. Two new plumage mutations in the Japanese quail: "curly" feather and "rusty" plumage. BMC Genetics, 6: 14.

- Nadeau N.J., Minvielle F., Mundy N.I. 2006. Association of a Glu92Lys substitution in MC1R with extended brown in Japanese quail ( Coturnix japonica). Animal Genetics, 37: 287-289.

- Nadeau N.J., Mundy N.I., Gourichon D., Minvielle F. 2007. Association of a single-nucleotide substitution in TYRP1 with roux in Japanese quail (Coturnix japonica). Animal Genetics, 38: 609-613.

- Nadeau, N.J., Minvielle F., Ito S., Inoue-Murayama M., Gourichon D., Johns S.A., Burke T., Mundy N.I. 2008. Characterization of Japanese Quail dominant yellow as a Genomic Deletion Upstream of the Avian Homologue of the Mammalian ASIP (agouti) Gene. Genetics, 178: 777-786.

- Vaez M., Follett S.A., Bed'hom B., Gourichon D., Tixier-Boichard M., Burke T. 2008. A single point-mutation within the melanophilin gene causes the lavender plumage colour dilution phenotype in the chicken. BMC Genetics, 9: 7.