F. Rouzaud et al., A first genotyping assay of French cattle breeds based on a new allele of the extension gene encoding the melanocortin-1 receptor (Mc1r), GEN SEL EVO, 32(5), 2000, pp. 511-520
The seven transmembrane domain melanocortin-1 receptor (Mc1r) encoded by th
e coat color extension gene (E) plays a key role in the signaling pathway o
f melanin synthesis. Upon the binding of agonist (melanocortin hormone, alp
ha -MSH) or antagonist (Agouti protein) ligands, the melanosomal synthesis
of eumelanin and/or phaeomelanin pigments is stimulated or inhibited, respe
ctively. Different alleles of the extension gene were cloned from unrelated
animals belonging to French cattle breeds and sequenced. The wild type E a
llele was mainly present in Normande cattle, the dominant ED allele in anim
als with black color (i.e. Holstein), whereas the recessive e allele was id
entified in homozygous animals exhibiting a more or less strong red coat co
lor (Blonde d'Aquitaine, Charolaise, Limousine and Salers). A new allele, n
amed El was found in either homozygous (E-1/E-1) or heterozygous (E-1/E) in
dividuals in Aubrac and Gasconne breeds. This allele displayed a 4 amino ac
id duplication (12 nucleotides) located within the third cytoplasmic loop o
f the receptor, a region known to interact with G proteins. A first genotyp
ing assay of the main French cattle breeds is described based on these four
extension alleles.