Intercellular signaling in embryonic and postnatal mammary gland development

描述(申请人提供)：我们的目标是剖析乳腺组织最初规范所涉及的细胞间信号机制，以及那些在乳腺发育的后续阶段调节增殖、分支形态发生和细胞极性的机制。乳腺癌涉及细胞过程的失调，如在乳腺发育过程中正常发生的增殖、细胞粘附性和运动性改变，以及上皮细胞侵入间质。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，以及提高我们对发育综合征的理解。这项建议侧重于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调节失调，当过度激活时，会导致小鼠的乳腺肿瘤。我们已经证明，WNT/β-catenin信号在胚胎发育中启动乳腺胎盘的形成是必不可少的。WNT/β-catenin信号活性最初在胚胎乳腺线上的宽条纹中被激活，逐渐在乳腺胎盘形成部位上调，并在胎盘部位之间下调。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是必不可少的。我们发现，分泌的WNT抑制物Dickkopf4在表面外胚层中受WNT调控，并在乳腺发育的早期表达，表明它可能是WNT活性的负反馈调节因子。我们将使用功能获得和功能丧失的方法来检验Dkk4是限制乳房安慰剂的大小和间距所必需的假设。我们发现，WNT/β-catenin信号在胚胎乳腺发育后期重新激活，伴随着乳腺雏形的初始分支。我们将使用遗传学方法来确定WNT信号是否对这种最初的分支形态发生是必要的。我们发现，WNT/β-catenin信号在青春期是活跃的，当腺体经历广泛的导管生长和分支时，对雌激素的反应。我们将测试这一假设，即WNT信号是青春期祖细胞扩张所必需的，支持在这个阶段发生的实质性生长。最后，由于引导β-连环蛋白非依赖性信号通路的非典型WNT配体在乳腺组织中动态表达，并在乳腺癌中表现出表达的改变，我们假设非典型WNT信号在乳腺发育中起作用。我们将通过检查非规范途径组件的零突变对体内乳腺发育的影响来检验这一假说。

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.