Intercellular signaling in embryonic and postnatal mammary gland development

描述（由申请人提供）：我们的目标是剖析乳腺组织初始规范中的细胞间信号机制，以及在乳腺发育的连续阶段中调节增殖、分支形态发生和细胞极性的细胞间信号机制。乳腺癌涉及细胞过程的失调，如增殖、细胞粘附和运动的改变以及上皮细胞向基质的侵袭，这些在乳腺发育过程中正常发生。因此，描述乳腺形态发生的分子机制将有助于确定新的乳腺癌治疗靶点，并提高我们对发育综合征的理解。本研究的重点是WNT/ β -连环蛋白信号通路在正常乳腺发育中的作用，该信号通路在乳腺癌中失调，当过度激活时，会导致小鼠乳腺肿瘤。我们已经证明，WNT/ β -连环蛋白信号对于胚胎发生中乳房基板形成的起始至关重要。WNT/ β -连环蛋白信号活性最初在沿胚胎乳腺系的宽条纹中被激活，并逐渐在乳腺基板形成位点上调，在基板位点之间下调。WNT活性的负向调控对于控制器官大小、防止异位乳腺的形成和抑制肿瘤发生的潜力至关重要。我们发现分泌的WNT抑制剂Dickkopf 4在表面外胚层受WNT调控，并在乳腺发育的早期阶段表达，这表明它是WNT活性的潜在负反馈调节器。我们将使用功能增益和功能损失的方法来验证Dkk4是限制乳腺基板大小和间距所必需的假设。我们发现WNT/ β -连环蛋白信号在胚胎乳腺发育后期被重新激活，伴随着乳腺雏形的初始分支。我们将使用遗传方法来确定WNT信号是否对这种初始分支形态发生是必要的。我们发现WNT/ β - catenin信号在青春期活跃，此时腺体在雌激素的作用下经历了广泛的导管生长和分支。我们将验证这一假设，即WNT信号是青春期祖细胞扩张所必需的，这支持了这一阶段发生的实质性生长。最后，由于引导β -连环蛋白独立信号通路的非规范WNT配体在乳腺组织中以动态方式表达，并在乳腺癌中表现出表达改变，我们假设非规范WNT信号有助于乳腺发育。我们将通过检查非典型途径成分的零突变对体内乳腺发育的影响来验证这一假设。

DESCRIPTION (provided by applicant): Our goal is to dissect the intercellular signaling mechanisms involved in the initial specification of mammary gland tissue, and those that regulate proliferation, branching morphogenesis and cell polarity at successive stages of mammary development. Breast cancer involves dysregulation of cellular processes such as proliferation, changes in cell adhesion and motility, and invasion of epithelial cells into a stroma, that occur normally in mammary development. Delineating the molecular mechanisms underlying mammary morphogenesis will thus help to identify novel therapeutic targets for breast cancer, as well as improving our understanding of developmental syndromes. This proposal focuses on the role in normal mammary development of the WNT/beta-catenin signaling pathway, which is dysregulated in breast cancer and, when hyperactivated, causes mammary tumors in mice. We have shown that WNT/beta-catenin signaling is essential for initiation of mammary placode formation in embryogenesis. WNT/beta-catenin signaling activity is initially activated in broad streaks along the embryonic mammary lines, and gradually becomes upregulated at sites of mammary placode formation and downregulated between the placode sites. Negative regulation of WNT activity is essential to control organ size, prevent formation of ectopic mammary glands, and suppress the potential for tumorigenesis. We discovered that the secreted WNT inhibitor Dickkopf 4 is WNT-regulated in the surface ectoderm and is expressed at the earliest stages of mammary development, suggesting it as a potential negative feedback regulator of WNT activity. We will use gain and loss of function approaches to test the hypothesis that Dkk4 is required for limiting the size and spacing of mammary placodes. We find that WNT/beta-catenin signaling is reactivated later in embryonic mammary development, accompanying the initial branching of the mammary rudiment. We will use genetic approaches to determine whether WNT signaling is necessary for this initial branching morphogenesis. We discovered that WNT/beta- catenin signaling is active in puberty when the gland undergoes extensive ductal outgrowth and branching in response to estrogen. We will test the hypothesis that WNT signaling is required for progenitor cell expansion in puberty that supports the substantial growth occurring at this stage. Finally, as non-canonical WNT ligands that direct beta-catenin independent signaling pathways are expressed in a dynamic fashion in mammary tissue and show altered expression in breast cancer, we hypothesize that non-canonical WNT signaling contributes to mammary development. We will test this hypothesis by examining the effects of null mutations of non-canonical pathway components on mammary development in vivo.