Transcription profiling of mouse mammary gland at key stages in development

The transition from pregnancy to lactation is a critical event in the survival of the newborn since all the nutrient requirements of the infant are provided by milk. While milk contains numerous components, including proteins, that aid in maintaining the health of the infant, lactose and milk fat represent the critical energy providing elements of milk. Much of the research to date on mammary epithelial differentiation has focused upon expression of milk protein genes, providing a somewhat distorted view of alveolar differentiation and secretory activation. While expression of milk protein genes increases during pregnancy and at secretory activation, the genes whose expression is more tightly regulated at this transition are those that regulate lipid biosynthesis. The sterol regulatory element binding protein (SREBP) family of transcription factors is recognized as regulating fatty acid and cholesterol biosynthesis. We propose that SREBP1 is a critical regulator of secretory activation with regard to lipid biosynthesis, in a manner that responds to diet, and that the serine/threonine protein kinase Akt influences this process, resulting in a highly efficient lipid synthetic organ that is able to support the nutritional needs of the newborn. Experiment Overall Design: Key points are examined in a time series of FVB mouse mammary gland development, secretory activation, lactation and involution. Quadruplicate mice (four biological replicates) at each time point were used for statistical power totaling 40 individual arrays in this study. Mice were as staged pregnant day 1 the day that post coital plug was observed, and similarly, lactation day 1 was the first day after birth. Involution day 2 is a forced weening model, where day 9 lactating dams had their litters removed for two days and then the dams were killed.从妊娠向泌乳的转变是新生幼崽存活的关键事件，因为幼崽的全部营养需求均由乳汁供给。乳汁虽包含诸多有助于维持幼崽健康的组分（包括蛋白质），但乳糖与乳脂肪才是乳汁中提供核心能量的物质。迄今为止，针对乳腺上皮细胞分化（mammary epithelial differentiation）的多数研究均聚焦于乳蛋白基因的表达，这使得我们对腺泡分化（alveolar differentiation）与分泌激活（secretory activation）的认知存在一定偏差。尽管乳蛋白基因的表达在妊娠期间及分泌激活时会有所上调，但在该转变过程中表达受到更严格调控的基因，实则是那些调控脂质生物合成的基因。现已证实，固醇调节元件结合蛋白（sterol regulatory element binding protein, SREBP）家族转录因子可调控脂肪酸与胆固醇的生物合成。我们提出假说：固醇调节元件结合蛋白1（SREBP1）是泌乳分泌激活过程中脂质生物合成的关键调控因子，其调控活性可响应膳食变化；而丝氨酸/苏氨酸蛋白激酶Akt（serine/threonine protein kinase Akt）会参与调控这一过程，最终形成可满足新生幼崽营养需求的高效脂质合成器官。 **实验总体设计**：本研究通过时间序列实验，对FVB品系小鼠的乳腺发育、分泌激活、泌乳及乳腺退化过程中的关键节点进行探究。每个时间点均使用4只生物学重复小鼠，本研究总计使用40张个体基因芯片以保障统计效力。小鼠的妊娠第1天定义为观察到交配栓的当日；泌乳第1天为幼崽出生后的首日。泌乳退化第2天采用强制断乳模型：对泌乳第9天的母鼠移除幼崽饲养2天后，处死母鼠进行采样。