Gautier M, Capitan A, Fritz S, Eggen A, Boichard D, Druet T
INRA, UR339 Laboratoire de Génétique Biochimique et Cytogénétique, F-78352 Jouy-en-Josas, France.
J Dairy Sci. 2007 Jun;90(6):2980-8. doi: 10.3168/jds.2006-707.
A quantitative trait locus (QTL) underlying different milk production traits has been identified with a high significance threshold value in the genomic region containing the acylCoA:diacylglycerol acyltransferase (DGAT1) gene, in the 3 main French dairy cattle breeds: French Holstein, Normande, and Montbéliarde. Previous studies have confirmed that the K232A polymorphism in DGAT1 is responsible for a major QTL underlying several milk production traits in Holstein dairy cattle and several other bovine breeds. In this study, we estimate the frequency of the 2 alternative alleles, K and A, of the K232A polymorphism in French Holstein, Normande, and Montbéliarde breeds. Although the K allele segregates in French Holstein and Normande breeds with a similar effect on production traits, the existence of additional mutations contributing to the observed QTL effect is strongly suggested in both breeds by the existence of sires heterozygous at the QTL but homozygous at the K232A polymorphism. One allele at a variable number of tandem repeats (VNTR) locus in the 5' noncoding region of DGAT1 has been recently proposed as a putative causative variant. In our study, this marker was found to present a high mutation rate of 0.8% per gamete and per generation, making the allele diversity observed compatible with that expected under neutrality. Moreover, among the sires homozygous at the K232A polymorphism, no allele at the VNTR can fully explain their QTL status. Finally, no allele at the VNTR was found to be significantly associated with the fat percentage variation in the 3 breeds simultaneously after correction for the effect of the K232A polymorphism. Therefore, our results suggest the existence of at least one other causative polymorphism not yet described. Because the A allele is nearly fixed in the Montbéliarde breed, this breed represents an interesting model to identify and confirm other mutations that have a strong effect on milk production traits.
在包含酰基辅酶A：二酰基甘油酰基转移酶（DGAT1）基因的基因组区域中，已在法国3个主要奶牛品种（法国荷斯坦牛、诺曼底牛和蒙贝利亚尔牛）中确定了一个影响不同产奶性状的数量性状基因座（QTL），其显著性阈值很高。先前的研究已证实，DGAT1基因中的K232A多态性是荷斯坦奶牛及其他几个牛品种中影响多个产奶性状的一个主要QTL的成因。在本研究中，我们估计了法国荷斯坦牛、诺曼底牛和蒙贝利亚尔牛品种中K232A多态性的2个等位基因K和A的频率。尽管K等位基因在法国荷斯坦牛和诺曼底牛品种中分离，对生产性状有类似影响，但在这两个品种中，QTL处杂合但K232A多态性处纯合的公牛的存在强烈表明，存在其他导致观察到的QTL效应的突变。DGAT1基因5'非编码区可变数目串联重复（VNTR）位点的一个等位基因最近被认为是一个可能的致病变异。在我们的研究中，发现该标记的突变率很高，每个配子和每代的突变率为0.8%，使得观察到的等位基因多样性与中性条件下预期的一致。此外，在K232A多态性处纯合的公牛中，VNTR的任何一个等位基因都不能完全解释它们的QTL状态。最后，在校正K232A多态性的影响后，未发现VNTR的任何一个等位基因与这3个品种的脂肪百分比变异同时存在显著关联。因此，我们的结果表明至少存在一个尚未描述的其他致病变多态性。由于A等位基因在蒙贝利亚尔牛品种中几乎固定，该品种是识别和确认对产奶性状有强烈影响的其他突变的一个有趣模型。
