Cosenza Gianfranco, Gallo Daniela, Auzino Barbara, Gaspa Giustino, Pauciullo Alfredo
Department of Agriculture, University of Napoli Federico II, Portici, Italy.
Department of Agricultural, Forest and Food Sciences, University of Torino, Grugliasco, Italy.
Front Genet. 2021 Feb 4;11:622494. doi: 10.3389/fgene.2020.622494. eCollection 2020.
The αs2-casein is one of the phosphoproteins secreted in all ruminants' milk, and it is the most hydrophilic of all caseins. However, this important gene () has not been characterized in detail in buffaloes with only two alleles detected (reported as alleles A and B), and no association studies with milk traits have been carried out unlike what has been achieved for other species of ruminants. In this study, we sequenced the whole gene of two Mediterranean river buffalo homozygotes for the presence/absence of the nucleotide C (g.7539G>C) realized at the donor splice site of exon 7 and, therefore, responsible for the skipping of the same exon at mRNA level (allele B). A high genetic variability was found all over the two sequenced alleles. In particular, 74 polymorphic sites were found in introns, six in the promoter, and three SNPs in the coding region (g.11072C>T, g.12803A>T, and g.14067A>G) with two of them responsible for amino acid replacements. Considering this genetic diversity, those found in the database and the SNP at the donor splice site of exon 7, it is possible to deduce at least eight different alleles ( A, B, B1, B2, C, D, E, and F) responsible for seven different possible translations of the buffalo αs2-casein. Haplotype data analysis suggests an evolutionary pathway of buffalo gene consistent with our proposal that the published allele A is the ancestral αs2-CN form, and the B2 probably arises from interallelic recombination (single crossing) between the alleles D and B (or B1). The allele C is of new identification, while B, B1, and B2 are deleted alleles because all are characterized by the mutation g.7539G>C. Two SNPs (g.7539G>C and g.14067A>G) were genotyped in 747 Italian buffaloes, and major alleles had a relative frequency of 0.83 and 0.51, respectively. An association study between these SNPs and milk traits including fatty acid composition was carried out. The SNP g.14067A>G showed a significant association ( < 0.05) on the content of palmitic acid in buffalo milk, thus suggesting its use in marker-assisted selection programs aiming for the improvement of buffalo milk fatty acid composition.
αs2-酪蛋白是所有反刍动物乳汁中分泌的磷蛋白之一，也是所有酪蛋白中亲水性最强的。然而，这个重要基因（）在水牛中尚未得到详细表征，仅检测到两个等位基因（报道为等位基因A和B），并且与其他反刍动物不同，尚未开展与乳性状的关联研究。在本研究中，我们对两头地中海河流域水牛纯合子的整个基因进行了测序，以确定外显子7供体剪接位点处核苷酸C（g.7539G>C）的有无，该核苷酸在mRNA水平上导致同一外显子的跳跃（等位基因B）。在两个测序的等位基因中均发现了高度的遗传变异性。具体而言，在内含子中发现了74个多态性位点，启动子中有6个，编码区有3个单核苷酸多态性（g.11072C>T、g.12803A>T和g.14067A>G），其中两个导致氨基酸替换。考虑到这种遗传多样性、数据库中发现的多样性以及外显子7供体剪接位点处的单核苷酸多态性，可以推断至少有八个不同的等位基因（A、B、B1、B2、C、D、E和F），它们负责水牛αs2-酪蛋白的七种不同可能翻译。单倍型数据分析表明，水牛基因的进化途径与我们的提议一致，即已发表的等位基因A是αs2-CN的祖先形式，B2可能源于等位基因D和B（或B1）之间的等位基因间重组（单交换）。等位基因C是新鉴定出来的，而B、B1和B2是缺失等位基因，因为它们都具有g.7539G>C突变。在747头意大利水牛中对两个单核苷酸多态性（g.7539G>C和g.14067A>G）进行了基因分型，主要等位基因的相对频率分别为0.83和0.51。开展了这些单核苷酸多态性与包括脂肪酸组成在内的乳性状之间的关联研究。单核苷酸多态性g.14067A>G在水牛奶中棕榈酸含量上显示出显著关联（<0.05），因此表明其可用于旨在改善水牛奶脂肪酸组成的标记辅助选择计划。
