Cellular and Molecular Mechanisms of Patterned Growth of the Mammalian Skull

描述（由申请人提供）：这是一项研究复杂的多组分结构（哺乳动物颅骨穹窿）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，该提案重点关注不同迁移间充质细胞群之间的相互作用如何调节模式生长。在颅骨穹窿发育过程中，来自神经嵴和中胚层的细胞迁移到眼睛上方、大脑和非成骨头部中胚层之间的位置。在那里，为了响应未知的线索，它们合并成额骨和顶骨的雏形，并向顶部扩展，最终与配对的对应物并置。尽管这些事件已被大致记录下来，但人们对它们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基本伸长中发挥作用，骨骼的模式是如何确定的，以及哪些过程控制额叶和顶叶骨原基的初始规格和分化。长期以来，人们一直认为神经嵴和中胚层之间的相互作用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。我们有三个具体目标：首先，我们将研究新定义的迁移性成骨前体细胞群体的特性、细胞动力学和命运，这些细胞有助于额骨和顶骨。我们将继续开展diI标记实验与注射胚胎的宫外发育相结合，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雏形通过预先存在的非成骨间质层的伸长而发生的。我们将检验这样的假设：MOP 细胞起源于与正在发育的额骨和顶骨雏形相邻的一群表达头蛋白的细胞。在第二个具体目标中，我们将检验这样的假设：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。我们将继续测试以下观点：神经嵴中需要 Msx1/2 才能实现额骨雏形的顶端扩张，并且 MOP 细胞生活史的变化会导致 Msx 突变体的背腹模式缺陷。我们还将研究神经嵴和中胚层中的相对活动 Msx2 控制额骨和顶骨的形状、冠状缝的位置以及沿 a/p 轴的图案的机制。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，以及测试 Msx1/2 和 FoxC1 之间的遗传相互作用。我们还将检验以下假设：FoxC1 直接与 Msx2 启动子中的 Bmp 响应元件相互作用，负向调节 Msx2 对 Bmp 信号传导的响应。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，包括家族性顶孔和颅缝早闭。公共健康相关性：这是一项研究头骨如何形成以及两个基因（Msx2 和 Msx2）如何控制头骨形状的提案。 MSX 基因特别令人感兴趣，因为携带 MSX2 和 MSX2 突变的人类患有先天缺陷，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 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.