Cellular and Molecular Mechanisms of Patterned Growth of the Mammalian Skull

描述（由申请人提供）：这是一份研究复杂、多组分结构哺乳动物头骨拱顶形态发生过程中模式生长的遗传控制的提案。更广泛地说，这一建议侧重于不同迁移间充质细胞群体之间的相互作用如何调节模式生长。在颅骨拱顶发育过程中，来自神经嵴和中胚层的细胞迁移到眼睛上方、大脑和非成骨性头部中胚层之间的位置。在那里，在对未知线索的反应中，它们合并成额骨和顶骨雏形，并向顶端扩张，最终与成对的对等体形成对立。尽管这些事件已被广泛地记录下来，但人们对其背后的发育机制知之甚少。尚未解决的关键问题包括细胞迁移是否在雏形延伸中起作用，骨骼的模式是如何确定的，以及什么过程控制了额骨和顶骨原素的初始规范和分化。神经嵴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头骨图案仍不清楚。在此，我们建议解决这些问题。我们有三个具体目标：首先，我们将研究新定义的迁移成骨前体细胞群的特性、细胞动力学和命运，这些细胞群有助于额骨和顶骨的形成。我们将继续开展diI标记实验，并结合注射胚胎的体外发育来评估迁移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：生长是由成骨细胞的雏形通过预先存在的非成骨间质层的延伸而发生的。我们将验证MOP细胞起源于与发育中的额骨和顶骨雏形相邻的表达noggin的细胞群体的假设。在第二个特定目标中，我们将验证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模式至关重要的假设。我们将继续测试Msx /2在额骨基础顶端扩张的神经嵴中所必需的想法，以及MOP细胞生活史的变化有助于Msx突变体的背-腹侧模式缺陷。我们还将研究神经嵴和中皮层的相对活动Msx2控制额骨和顶骨形状、冠状缝线位置以及沿a/p轴方向的机制。在最后的具体目标中，我们将研究FoxC1和Msx1/2之间的相互作用，该相互作用揭示了一个信号网络，通过该信号网络，邻近大脑的细胞层控制额骨和顶骨祖细胞群的发育。这将需要进一步表征FoxC1突变体，并测试Msx1/2和FoxC1之间的遗传相互作用。我们还将测试FoxC1直接与Msx2启动子中的Bmp响应元件相互作用的假设，负向调节Msx2对Bmp信号的响应。这项工作的意义在于，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闭闭。公共卫生相关性：这是一项研究颅骨如何形成以及两个基因msx2和msx2如何控制颅骨骨骼形状的建议。Msx基因之所以受到特别关注，是因为MSX2和MSX2基因突变的人会产生先天缺陷，影响他们的头骨和牙齿。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Msx1和ms2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这种出生缺陷的新方法。

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.