Variation in the Fatty Acid Synthase Gene (FASN) and Its Association with Milk Traits in Gannan Yaks

SIMPLE SUMMARY: The yak (Bos grunniens) is a symbolic animal living in alpine climates (between 2000 to 5000 m) in the Qinghai–Tibetan Plateau. More than 13 million domestic yaks provide the basic resources (such as meat, milk, hair, transportation, and dung for fuel) necessary for Tibetans and nomads in China. While yak milk production is not elevated, yak milk is superior to dairy cow milk in nutrient composition (protein and fat). Fatty acid synthase (FASN) is an enzyme involved in the synthesis of fatty acids (FA) and plays a central role in de novo lipogenesis in mammals. However, there have been few reports on the effects of the FASN gene on the milk traits of yak. Our study elucidated the tissue expression of the yak FASN gene and the association of variants and haplotypes in the gene with milk fat percentage and total milk solid percentage. The results provide guidance for the molecular-assisted selection of milk traits in yaks. ABSTRACT: Fatty acid synthase (FASN) is an enzyme involved in the synthesis of fatty acids (FA) and plays a central role in de novo lipogenesis in mammals. This study was conducted to ascertain the relative level of expression of the FASN gene (FASN) in tissues from the yak (Bos grunniens), and to search for variation in two regions of yak FASN using polymerase chain reaction single-stranded conformational polymorphism (PCR-SSCP) analyses; it also ascertains whether that variation is associated with yak milk traits. The gene was found to be expressed in twelve tissues, with the highest expression detected in the mammary gland, followed by subcutaneous fat tissue. Two regions of the gene were analyzed in 290 Gannan yaks: A region spanning exon 24-intron 24 and a region spanning exon 34. These regions both produced two PCR-SSCP patterns, which, upon sequencing, represented different DNA sequences. This sequence variation resulted from the presence of three nucleotide substitutions: c.4296+38C/T (intron 24), c.5884A/G, and c.5903G/A, both located in exon 34. The exon 34 substitutions would result in the amino acid substitutions p.Thr1962Ala and p.Gly1968Glu if expressed. Four haplotypes spanning from the exon 24-intron 24 region to exon 34 were identified. Of these, two were common (A(1)-A(2) and B(1)-A(2)), and two were rare (A(1)-B(2) and B(1)-B(2)) in the yaks investigated. The presence of A(1)-A(2) was associated with an increase in milk fat content (p = 0.050) and total milk solid content (p = 0.037), while diplotype A(1)-A(2)/B(1)-A(2) had a higher milk fat content (p = 0.038) than the other diplotypes. This study suggests that further characterization of the FASN gene might provide for an improved understanding of milk traits in yaks.