Delineating the role of insulin-like growth factor binding protein 7 in mammary gland development

与身体中的许多组织不同，乳腺在青春期后达到其全部功能。在青春期，乳腺扩张，形成一个复杂的导管网络和小的中空囊（肺泡结构）。在怀孕期间，乳腺经历进一步的结构变化，以产生新的导管结构和含有乳汁分泌细胞的扩大的肺泡囊，随后它退回到怀孕前阶段（退化）。在哺乳期间，腔细胞将进一步分化为产奶细胞，而肌上皮细胞在催产素的影响下收缩以诱导乳汁从肺泡囊喷射到导管中。在每个妊娠周期中乳腺的再生是由于乳腺干细胞及其直接后代（祖细胞）的特殊功能。虽然已经做了很多研究来了解激素如雌激素、孕酮、催乳素和生长因子如胰岛素、胰岛素样生长因子（IGFs）及其结合蛋白（Igfbps）在乳腺发育中的功能，但对这些因子在调节乳腺干细胞和祖细胞功能中发挥的潜在作用知之甚少。拟议研究计划的总体目标是确定调节乳腺干细胞特殊功能（增殖，分化和自我更新）的分子机制。* * 虽然IGFs在乳腺发育和成熟中的作用已被描述，但Igfbps在这一过程中的作用尚未完全了解。为了确定Igfbp7在乳腺发育和成熟中的作用，我们产生了缺乏Igfbp7蛋白表达的小鼠。有趣的是，我们已经观察到，在Igfbp7的情况下，乳腺的发育在其他健康小鼠中受到显著影响。对这些小鼠的仔细检查显示，在3、6和11周的阶段乳腺发育迟缓，这与乳腺发育的青春期前和青春期后阶段相一致。最重要的是，我们已经观察到，在怀孕期间，Igfbp7无效腺体含有变形和小的肺泡结构，在哺乳期间，Igfbp7无效腺体表现出早熟退化的迹象。此外，我们观察到，在3个妊娠周期后，Igfbp7缺失小鼠的乳腺不含乳房结构。这一令人吃惊的特征表明，负责乳房结构再生的Igfpb7-null乳腺干细胞可能存在功能缺陷。在这项研究计划中，我们将检查Igfbp7的丢失是否影响了乳腺干细胞的频率和自我更新能力。此外，我们将确定参与Igfbp7调节乳腺发育的分子机制。这项研究计划将首次深入了解Igfbp7如何调节乳腺干细胞和乳腺发育的特殊功能。由于Igfbp7在乳腺正常发育中的作用尚未被研究，因此，尽管拟议的工作，但任何发现都将进一步加深我们对Igfbp7在这一复杂和高度协调的过程中的作用的认识。这项研究计划还将提供一个很好的机会，以培训和留住高素质的人员，因为它需要使用最先进的设备，并获得有关干细胞和乳腺发育研究的实验程序的独特技能，这是在马尼托巴省和加拿大缺乏。

Unlike many tissues in the body, mammary glands reach their full functional capacity after puberty. Upon puberty the mammary glands expand to create an elaborated network of ducts and small hollow sacs (alveolar structures). During pregnancy, the mammary gland undergoes further structural changes to create new ductal structures and enlarged alveolar sacs that contain milk-secreting cells and subsequently it recede to the pre-pregnant stage (involution). During lactation, the luminal cells will further differentiate into milk-producing cells while the myoepithelial cells, under the influence of oxytocin contract to induce milk ejection from the alveolar sacs into the ducts. The regeneration of mammary glands during each pregnancy cycle is due to the special functions of breast stem cells and their immediate progeny, the progenitor cells. While much studies have been done to understand the function of hormones such as estrogen, progesterone, prolactin, and growth factors such as insulin, Insulin-like Growth Factors (IGFs) and their binding proteins (Igfbps) in mammary gland development, very little is know about the potential roles that these factors play in regulating breast stem and progenitor cell functions. The overall objective of the proposed research program is the to ascertain the molecular mechanisms that regulate the special functions (proliferation, differentiation, and self-renewal) of breast stem cells. **While the role of IGFs in mammary gland development and maturation has been described, the role of Igfbps in this process is not well understood. To ascertain the role of Igfbp7 in mammary gland development and maturation, we generated mice lacking expression of Igfbp7 protein. Interestingly, we have observed that in absence of Igfbp7, the development of mammary glands is significantly affected in otherwise healthy mice. Close examination of these mice revealed mammary gland developmental retardation at 3, 6 and 11 weeks of stage which coincide with pre and post pubertal stages of mammary gland development. Most significantly, we have observed that during pregnancy, the Igfbp7-null glands contained deformed and small alveolar structures and during lactation the Igfbp7-null glands exhibit signs of precocious involution. Also, we have observed that after 3 pregnancy cycles, the mammary glands of the Igfbp7-null mice contained no breast structures. This startling feature suggests that Igfpb7-null breast stem cells that are responsible for the regeneration of the breast structures may be functionally defective. In this research program we will examine if loss of Igfbp7 has affected the frequency and self-renewal capacity of the breast stem cells. Moreover, we will ascertain the molecular mechanisms involved in the Igfbp7 regulation of mammary gland development. This research program then will provide the first insight into how Igfbp7 acts to regulate the special functions of breast stem cells and mammary gland development. Because the role of Igfbp7 in the normal development of mammary gland has not been studied, any findings though the proposed work will further our knowledge about role of Igfbp7 in this complicated and highly coordinated process.**This research program will also provide a great opportunity to train and retain highly-qualify personnel, as it requires the use of state of art equipment and acquiring unique skill sets in experimental procedures pertaining to the study of stem cells and mammary gland development that is lacking in the province of Manitoba and in Canada.