Molecular and pharmacological characterization of dominant black coat color in sheep |
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Authors: | Dag Inge Våge Helge Klungland Dongsi Lu Roger D Cone |
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Institution: | Department of Animal Science, Agricultural University of Norway, P.O. Box 5025, N-1432 ?s, Norway, NO The Vollum Institute, Oregon Health Sciences University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97201, USA, US
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Abstract: | Dominant black coat color in sheep is predicted to be caused by an allele E
D
at the extension locus. Recent studies have shown that this gene encodes the melanocyte stimulating hormone receptor (MC1-R). In mouse and
fox, naturally occurring mutations in the coding region of MC1-R produce a constitutively activated receptor that switches
the synthesis from phaeomelanin to eumelanin within the melanocyte, explaining the black coat color observed phenotypically.
In the sheep, we have identified a Met→Lys mutation in position 73 (M73K) together with a Asp → Asn change at position 121
(D121N) showing complete cosegregation with dominant black coat color in a family lineage. Only the M73K mutation showed constitutive
activation when introduced into the corresponding mouse receptor (mMC1-R) for pharmacological analysis; however, the position
corresponding to D121 in the mouse receptor is required for high affinity ligand binding. The pharmacological profile of the
M73K change is unique compared to the constitutively active E92K mutation in the sombre mouse and C123R mutation in the Alaska
silver fox, indicating that the M73K change activates the receptor via a mechanism distinct from these previously characterized
mutations.
Received: 18 September 1997 / Accepted: 14 October 1998 |
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