A first genotyping assay of French cattle breeds based on a new allele of the extension gene encoding the melanocortin-1 receptor (Mc1r)

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.