Department of Animal Science, University of California Davis, Davis, California, United States of America.
PLoS One. 2011 Apr 25;6(4):e18895. doi: 10.1371/journal.pone.0018895.
This study examines the genes coding for enzymes involved in bovine milk oligosaccharide metabolism by comparing the oligosaccharide profiles with the expressions of glycosylation-related genes. Fresh milk samples (n = 32) were collected from four Holstein and Jersey cows at days 1, 15, 90 and 250 of lactation and free milk oligosaccharide profiles were analyzed. RNA was extracted from milk somatic cells at days 15 and 250 of lactation (n = 12) and gene expression analysis was conducted by RNA-Sequencing. A list was created of 121 glycosylation-related genes involved in oligosaccharide metabolism pathways in bovine by analyzing the oligosaccharide profiles and performing an extensive literature search. No significant differences were observed in either oligosaccharide profiles or expressions of glycosylation-related genes between Holstein and Jersey cows. The highest concentrations of free oligosaccharides were observed in the colostrum samples and a sharp decrease was observed in the concentration of free oligosaccharides on day 15, followed by progressive decrease on days 90 and 250. Ninety-two glycosylation-related genes were expressed in milk somatic cells. Most of these genes exhibited higher expression in day 250 samples indicating increases in net glycosylation-related metabolism in spite of decreases in free milk oligosaccharides in late lactation milk. Even though fucosylated free oligosaccharides were not identified, gene expression indicated the likely presence of fucosylated oligosaccharides in bovine milk. Fucosidase genes were expressed in milk and a possible explanation for not detecting fucosylated free oligosaccharides is the degradation of large fucosylated free oligosaccharides by the fucosidases. Detailed characterization of enzymes encoded by the 92 glycosylation-related genes identified in this study will provide the basic knowledge for metabolic network analysis of oligosaccharides in mammalian milk. These candidate genes will guide the design of a targeted breeding strategy to optimize the content of beneficial oligosaccharides in bovine milk.
本研究通过比较寡糖谱和糖基化相关基因的表达，研究了参与牛初乳寡糖代谢的酶的编码基因。从 4 头荷斯坦和泽西奶牛的泌乳第 1、15、90 和 250 天采集新鲜牛奶样本（n=32），并分析游离乳寡糖谱。从泌乳第 15 和 250 天的牛奶体细胞中提取 RNA（n=12），并通过 RNA 测序进行基因表达分析。通过分析寡糖谱并进行广泛的文献检索，列出了参与牛寡糖代谢途径的 121 个糖基化相关基因。在荷斯坦和泽西奶牛之间，无论是寡糖谱还是糖基化相关基因的表达都没有观察到显著差异。初乳样本中游离寡糖浓度最高，第 15 天游离寡糖浓度急剧下降，随后在第 90 和 250 天逐渐下降。92 个糖基化相关基因在牛奶体细胞中表达。这些基因中的大多数在第 250 天样本中表达较高，表明尽管在泌乳后期牛奶中游离乳寡糖减少，但净糖基化相关代谢增加。尽管未鉴定出岩藻糖基化游离寡糖，但基因表达表明牛乳中可能存在岩藻糖基化寡糖。在牛奶中表达了岩藻糖苷酶基因，无法检测到岩藻糖基化游离寡糖的一个可能解释是岩藻糖苷酶降解了大的岩藻糖基化游离寡糖。本研究中鉴定的 92 个糖基化相关基因所编码的酶的详细特征将为哺乳动物乳中寡糖代谢网络分析提供基础知识。这些候选基因将指导设计有针对性的选育策略，以优化牛乳中有益寡糖的含量。
