Mammary transcriptome analysis of lactating dairy cows . Bos taurus

Growth hormone (GH) has a well established galactopoietic effect on ruminant lactation, however the molecular mechanisms that mediate these effects are not fully understood. This study aimed to define the effects of GH on the production of milk protein by the bovine mammary gland and to establish the potential molecular mechanisms mediating these effects. Elevated levels of GH increased milk yield with corresponding increases in protein, fat and lactose yield, while milk composition remained unaffected by treatment. Increased yield (but not concentration) of all the individual milk proteins was not accompanied by changes in the levels of the milk protein transcripts, with the exception of S2-casein, suggesting post-transcriptional regulation of the milk protein genes is a main factor in the GH-mediated effects on bovine lactation. There were significant transcriptional changes in a wide range of pathways including cell signaling, cell death, cell growth and proliferation, cell cycle regulation and metabolism, consistent with the broad effects of GH. Differential expression of genes involved in the PI3K, ERK/MAPK, insulin receptor, JAK/STAT and IGF-1 signaling pathways were also evident in response to GH treatment supporting potential cross-talk between the GH and insulin signaling pathways in the bovine mammary gland. Transcript levels of the SHC1 gene were elevated in GH-treated cows. SHC1 activates many pathways including those associated with translational regulation and gene transcription and has been implicated in mediating cross-talk between the insulin and GH signaling pathways, providing some insights into the potential pathways mediating the effects of GH on milk protein synthesis in the bovine mammary gland. Overall design: Eight non-pregnant second lactation spring-calved Jersey cows between 178 to 200 days postpartum, were sourced from a commercial herd. Cows were weighed twice weekly for one month prior to treatment, and randomly assigned to two groups of four. On day 0, a slow-release formula of commercially available GH (Lactatropin®, Elanco Animal Health, Bryanston, South Africa) was administered via a single subcutaneous injection to 4 lactating Jersey cows. A further 4 Jersey cows were given a single subcutaneous injection of saline as controls. 18 slides were used in a loop design which requires three aliquots of each test sample labeled alternately with the Cy5 and Cy3 dyes and co-hybridized on arrays with two other test samples.

生长激素（Growth hormone, GH）对反刍动物泌乳具有公认的促乳腺泌乳效应，但其介导该效应的分子机制尚未完全阐明。本研究旨在明确生长激素对牛乳腺乳汁蛋白生成的影响，并解析介导该效应的潜在分子机制。升高的生长激素水平提升了产奶量，同时伴随乳蛋白、乳脂及乳糖产量的增加，但乳成分未受处理影响。各单体乳蛋白的产量（而非浓度）均有所提升，但除S2-酪蛋白（S2-casein）外，其余乳蛋白的转录本水平未发生相应变化，这提示乳蛋白基因的转录后调控是生长激素介导牛泌乳效应的主要因素。多种通路均出现显著转录变化，包括细胞信号转导、细胞死亡、细胞生长与增殖、细胞周期调控及代谢通路，与生长激素的广谱效应一致。针对生长激素处理的应答中，PI3K、ERK/MAPK、胰岛素受体、JAK/STAT及IGF-1信号通路相关基因的差异表达同样显著，支持牛乳腺中生长激素与胰岛素信号通路间存在潜在交叉对话。经生长激素处理的奶牛中，SHC1基因的转录本水平升高。SHC1可激活多条通路，包括与翻译调控及基因转录相关的通路，且已被证实参与介导胰岛素与生长激素信号通路间的交叉对话，为解析生长激素调控牛乳腺乳蛋白合成的潜在通路提供了新的见解。总体实验设计：本研究从商业牛群中选取8头处于产后178至200天、处于第二泌乳期的未妊娠泽西奶牛。处理前1个月内，每周对奶牛称重两次，并随机分为两组，每组4头。第0天，向4头泌乳泽西奶牛单次皮下注射市售缓释型生长激素制剂（Lactatropin®，Elanco Animal Health，南非布赖恩斯顿）。其余4头奶牛则单次皮下注射生理盐水作为对照组。本研究采用循环设计，共使用18张芯片：每个待测样本需制备三份等分试样，分别交替用Cy5与Cy3荧光染料标记，并与另外两份待测样本共同杂交至芯片上。