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颅骨穹窿复杂多组分结构形态发生过程中模式化生长的遗传控制的建议。更广泛地说，这项建议的重点是不同的迁移间充质细胞群体之间的相互作用如何调节模式化生长。在颅骨穹窿发育期间，来自神经嵴和中胚层的细胞迁移到眼睛上方的位置，在脑和非成骨头部中胚层层之间。在那里，为了回应未知的线索，它们合并成额骨和顶骨的雏形，并向顶部扩张，最终与它们配对的对应物并置。虽然这些事件已被记录在广泛的轮廓，很少有人知道的发展机制，他们的基础。尚未解决的关键问题包括细胞迁移是否在雏形延长中起作用，骨骼的模式是如何确定的，以及什么过程控制着额骨和顶骨原基的初始规格和分化。神经嵴和中胚层之间的相互作用一直被认为在这些过程中很重要，但这些相互作用如何甚至是否有助于头骨图案仍然不清楚。在此，我们建议解决这些问题。我们有三个具体目标：在第一，我们将调查的属性，细胞动力学，和一个新定义的人口迁移成骨前体细胞，有助于额骨和顶骨的命运。我们将继续进行diI标记实验，结合注射胚胎的子宫外发育，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：生长是通过成骨细胞的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细胞起源于邻近发育中的额骨和顶骨雏形的表达noggin的细胞群的假设。在第二个具体目标中，我们将检验神经嵴和中胚层之间的相互作用对于颅骨雏形的生长以及额骨和顶骨的前后和背腹图案化是必不可少的假设。我们将继续测试的想法，Msx 1/2需要在神经嵴的额骨雏形的顶端扩张，并在MOP细胞生活史的变化有助于背腹图案缺陷的Msx突变体。我们还将研究神经嵴和中胚层中Msx 2的相对活动控制额骨和顶骨的形状、冠状缝的位置，从而沿沿着a/p轴形成图案的机制。在最后的《特定目标》中，我们将研究FoxC 1和Msx 1/2之间的相互作用，该相互作用揭示了一个信号网络，邻近大脑的细胞层通过该网络控制额叶和顶叶骨祖细胞群的发育。这将需要FoxC 1突变体的进一步表征，以及Msx 1/2和FoxC 1之间的遗传相互作用的测试。我们还将测试的假设，FoxC 1直接与Bmp的响应元件在Msx 2启动子，负调节Msx 2的Bmp信号的响应。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，包括家族性顶骨孔和颅缝早闭症。公共卫生相关性：这是一项研究头骨如何形成以及两个基因Msx 2和Msx 2如何控制头骨形状的提议。Msx基因特别令人感兴趣，因为MSX 2和MSX 2突变的人具有影响头骨和牙齿的出生缺陷。通过研究这些基因如何工作，我们将更多地了解头骨发育的基本过程，以及Msx 1和Msx 2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这种出生缺陷的新治疗方法。

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.