Cellular and Molecular Mechanisms of Patterned Growth of the Mammalian Skull

描述(由申请人提供)：这是一项研究哺乳动物头盖骨拱顶复杂、多组分结构形态发生过程中图案化生长的遗传控制的提案。更广泛地说，这项建议侧重于不同的迁移间充质细胞群体之间的相互作用如何调控模式生长。在颅骨穹隆发育期间，来自神经脊和中胚层的细胞迁移到眼睛上方的位置，在大脑和一层非成骨的头部中胚层之间。在那里，作为对未知线索的反应，它们结合成额骨和顶骨的残骸，并在顶部扩张，最终与其配对的对应物并列。虽然这些事件已被大体记录在案，但人们对其背后的发展机制知之甚少。仍未解决的关键问题包括细胞迁移是否在胚胎的伸长中起作用，骨骼的模式是如何确定的，以及什么过程控制额骨和顶骨原的初始规格和分化。长期以来，神经脊和中胚层之间的相互作用在这些过程中一直被认为是重要的，但这些相互作用如何甚至是否有助于颅骨图案的形成仍不清楚。在这里，我们建议解决这些问题。我们有三个具体的目标：首先，我们将研究一个新定义的迁移性成骨前体细胞群体的性质、细胞动力学和命运，这些细胞对额骨和顶骨有贡献。我们将继续结合注射胚胎的体外发育进行DiI标记实验，以评估迁移性成骨前体细胞的命运和发育功能。我们将评估额骨和顶骨生长的潜在机制：这种生长是通过延长成骨细胞雏形穿过预先存在的非成骨间充质层而发生的。我们将检验MOP细胞起源于额骨和顶骨发育中的骨痂附近的一群noggin表达细胞的假设。第二个特定目的我们将检验神经脊和中胚层之间的相互作用对于头盖骨的生长和额骨和顶骨的前后部和背腹面模式是必不可少的假说。我们将继续测试这一想法，即Msx1/2是额骨雏形的顶端扩张所需的神经脊，以及MOP细胞生活史的变化导致MSX突变体的背腹图案缺陷。我们还将研究神经脊和中胚层中的相对活动MSX2控制额骨和顶骨的形状、冠状缝合的位置，从而沿着a/p轴形成图案的机制。在最终的特定目标中，我们将研究FoxC1和Msx1/2之间的相互作用，揭示了一个信号网络，通过这个网络，邻近大脑的细胞层控制着额骨和顶骨祖细胞群体的发育。这将需要对FoxC1突变体进行进一步的表征，以及测试Msx1/2和FoxC1之间的遗传相互作用。我们还将检验FoxC1直接与MSX2启动子中的BMP反应元件相互作用，负向调节MSX2对BMP信号的反应的假设。这项拟议工作的意义在于，它解决了模式形成的基本机制以及影响颅骨生长和模式的疾病的病理生理学，包括家族性顶孔和颅缝融合。与公共健康相关：这是一项研究头骨如何形成以及两个基因--MSX2和MSX2--如何控制头盖骨形状的建议。MSX基因之所以特别令人感兴趣，是因为带有MSX2和MSX2突变的人有先天缺陷，会影响他们的头骨和牙齿。通过研究这些基因的工作原理，我们将更多地了解头骨发育的基本过程，以及Msx1和Msx2的突变如何导致出生缺陷。从长远来看，这项工作可能有助于设计出治疗此类出生缺陷的新方法。

DESCRIPTION (provided by applicant): This is a proposal to investigate the genetic control of patterned growth during the morphogenesis of a complex, multicomponent structure, the mammalian skull vault. More broadly, this proposal focuses on how interactions between distinct migratory mesenchymal cell populations regulate patterned growth. During skull vault development, cells derived from the neural crest and mesoderm migrate into positions above the eye, between the brain and a layer of non-osteogenic head mesoderm. There, in response to unknown cues they coalesce into the frontal and parietal bone rudiments and expand apically, ultimately coming into apposition with their paired counterparts. Although these events have been documented in broad outline, little is known about the developmental mechanisms that underlie them. Key issues that remain unresolved include whether cell migration has a role in rudiment elongation, how the pattern of the bones is determined, and what processes control the initial specification and differentiation of the frontal and parietal bone anlagen. Interactions between neural crest and mesoderm have long been postulated to be important in these processes, but how or even whether these interactions contribute to skull patterning remains unclear. Here we propose to address these questions. We have three Specific Aims: In the first, we will investigate the properties, cellular dynamics, and fate of a newly-defined population of migratory osteogenic precursor cells that contribute to the frontal and parietal bones. We will continue to carry out diI labeling experiments in conjunction with exo utero development of injected embryos to assess the fate and developmental function of migratory osteogenic precursor cells. We will evaluate a potential mechanism of frontal and parietal bone growth: that growth occurs by elongation of a rudiment of osteogenic cells through a preexisting layer of non- osteogenic mesenchyme. We will test the hypothesis that MOP cells originate in a population of noggin- expressing cells adjacent to the developing frontal and parietal bone rudiments In the second Specific Aim We will test the hypothesis that interactions between neural crest and mesoderm are essential for the growth of the calvarial rudiments and the anterior-posterior and dorso-ventral patterning of the frontal and parietal bones. We will continue to test the idea that Msx1/2 are required in the neural crest for the apical expansion of the frontal bone rudiment, and that changes in MOP cell life history contribute to dorso-ventral patterning defects of Msx mutants. We will also examine the mechanism by which the relative activity Msx2 in the neural crest and mesoderm controls the shape of the frontal and parietal bones, the location of the coronal suture, and thus patterning along the a/p axis. In the final Specific Aim, we will examine an interaction between FoxC1 and Msx1/2 that has revealed a signaling network by which the cell layers adjacent to the brain control the development of the frontal and parietal bone progenitor populations. This will entail a further characterization of FoxC1 mutants, as well as tests for a genetic interaction between Msx1/2 and FoxC1. We will also test of the hypothesis that FoxC1 interacts directly with a Bmp-responsive element in the Msx2 promoter, negatively regulating the response of Msx2 to Bmp signaling. The significance of the proposed work is that it addresses fundamental mechanisms of pattern formation as well as the pathophysiology of disorders affecting the growth and patterning of calvarial bones, including familial parietal foramina and craniosynostosis. PUBLIC HEALTH RELEVANCE: This is a proposal to study how the skull forms and how two genes-Msx2 and Msx2-control the shape of bones of the skull. Msx genes are of special interest because humans with mutations in MSX2 and MSX2 have birth defects that affect their skulls and teeth. By studying how these genes work, we will learn more about basic processes of skull development as well as how mutations in Msx1 and 2 lead to birth defects. In the long term, this work may help to devise new treatments of such birth defects.