Boutinaud Marion, Jammes Hélène
Unité Mixte de Recherches sur la Production du Lait, INRA, 35590 Saint Gilles, France.
Domest Anim Endocrinol. 2004 Nov;27(4):363-78. doi: 10.1016/j.domaniend.2004.04.002.
In ruminants, both milking frequency and exogenous GH treatment affect milk production. In a previous report, we showed that the modulation of milk yield due to variations in milking frequency and GH treatment was associated with variations in mammary cell numbers. The aim of this study was to clarify the different mechanisms governing the effects of GH treatment and milking frequency on signal transducer and activator of transcription (Stat) expression and activation, and on the expression of genes involved in mammary cell differentiation. Six Saanen goats in late lactation were milked once daily from one half-udder and thrice daily from the other half-udder for 23 days. At the same time, the goats were divided into two groups: GH-treated versus control group. After slaughter of the goats, soluble mammary proteins and RNA were extracted from half-udder samples. Levels of Stat5, Stat3 and Stat1 proteins and the Stat activation by phosphorylation were analysed by Western blot. The amounts of Stat5 protein and mRNA were significantly elevated by GH treatment in all half-udders (milked once or thrice daily). Positive Stat5 immunoreactivity was principally localised in the nuclei of epithelial cells, with heterogeneous intensity between cells. No significant changes in Stat5 protein phosphorylation levels were observed. Furthermore, GH significantly increased Stat1 protein levels, without modifying the level of Stat1 tyrosine phosphorylation, and tended to reduce the abundance of Stat3 protein. In contrast, milking frequency failed to modify Stat gene expression, protein level and phosphorylation. Using Northern blot, we showed that levels of kappa casein and prolactin receptor mRNA were not affected by the treatments. These observations suggest that GH probably acts specifically on mammary cells by regulating the expression of Stat1, 3 and 5. In contrast, milking frequency does not act through this regulatory pathway.
在反刍动物中，挤奶频率和外源性生长激素（GH）处理均会影响产奶量。在之前的一份报告中，我们表明，由于挤奶频率和GH处理的变化而导致的产奶量调节与乳腺细胞数量的变化有关。本研究的目的是阐明GH处理和挤奶频率对信号转导和转录激活因子（Stat）表达与激活以及对参与乳腺细胞分化的基因表达产生影响的不同机制。六只处于泌乳后期的萨能山羊，一侧半个乳房每天挤奶一次，另一侧半个乳房每天挤奶三次，持续23天。同时，将山羊分为两组：GH处理组和对照组。山羊屠宰后，从半个乳房样本中提取可溶性乳腺蛋白和RNA。通过蛋白质印迹法分析Stat5、Stat3和Stat1蛋白的水平以及磷酸化介导的Stat激活情况。在所有半个乳房（每天挤奶一次或三次）中，GH处理均显著提高了Stat5蛋白和mRNA的水平。Stat5阳性免疫反应主要定位于上皮细胞核中，细胞间强度不均一。未观察到Stat5蛋白磷酸化水平的显著变化。此外，GH显著提高了Stat1蛋白水平，但未改变Stat1酪氨酸磷酸化水平，并且有降低Stat3蛋白丰度的趋势。相比之下，挤奶频率未能改变Stat基因表达、蛋白水平和磷酸化情况。通过Northern印迹法，我们表明κ-酪蛋白和催乳素受体mRNA的水平不受这些处理的影响。这些观察结果表明，GH可能通过调节Stat1、3和5的表达而特异性作用于乳腺细胞。相比之下，挤奶频率并非通过这一调节途径发挥作用。
