Intercellular signaling in embryonic and postnatal mammary gland development

描述（由申请人提供）：我们的目标是剖析参与乳腺组织初始特化的细胞间信号传导机制，以及在乳腺发育的连续阶段调节增殖、分支形态发生和细胞极性的细胞间信号传导机制。乳腺癌涉及细胞过程的失调，如增殖、细胞粘附和运动性的变化以及上皮细胞侵入基质，这些通常发生在乳腺发育中。因此，阐明乳腺形态发生的分子机制将有助于确定乳腺癌的新治疗靶点，并提高我们对发育综合征的理解。该提案重点关注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，并且当过度激活时，导致小鼠乳腺肿瘤。我们已经表明，WNT/β-连环蛋白信号是必不可少的启动乳腺基板形成胚胎发育。WNT/β-连环蛋白信号传导活性最初在沿着胚胎乳腺线的宽条纹中被激活，并在乳腺基板形成位点逐渐上调，在基板位点之间下调。WNT活性的负调节对于控制器官大小、防止异位乳腺的形成和抑制肿瘤发生的可能性至关重要。我们发现分泌的WNT抑制剂Dickkopf 4在表面外胚层中是WNT调节的，并且在乳腺发育的最早阶段表达，这表明它是WNT活性的潜在负反馈调节剂。我们将使用功能获得和丧失的方法来检验Dkk 4是限制乳腺基板的大小和间距所必需的假设。我们发现，WNT/β-catenin信号被重新激活后，在胚胎乳腺发育，伴随着最初的分支的乳房雏形。我们将使用遗传学方法来确定WNT信号是否是必要的，这种初始的分支形态发生。我们发现WNT/β-连环蛋白信号在青春期是活跃的，此时腺体经历广泛的导管生长和分支以响应雌激素。我们将检验这一假设，即WNT信号传导是支持在青春期发生的实质性生长的祖细胞扩增所必需的。最后，由于指导β-连环蛋白非依赖性信号通路的非经典WNT配体在乳腺组织中以动态方式表达，并且在乳腺癌中显示出改变的表达，我们假设非经典WNT信号传导有助于乳腺发育。我们将通过研究非经典途径成分的无效突变对体内乳腺发育的影响来检验这一假设。

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.