The role of BMP signaling in craniofacial cartilage development

项目摘要 颅面畸形在很大程度上归因于骨形成、迁移和分化的缺陷。 颅神经嵴细胞（CNCC）。由于CNCC是发育可塑性的，了解遗传和 控制CNCC的软骨细胞和成骨细胞谱系特化的分子途径是一种 这是解释颅面骨骼疾病病因的先决条件。在发现骨头之后 骨形态发生蛋白（BMP），许多优雅的研究已经揭示了它们在骨骼发育中的重要作用。 发展然而，目前还不清楚为什么BMP能够改变人的命运和谱系。 未分化的干细胞向成骨细胞转化。特别是，尽管BMP的重要性 在颅面骨发育过程中，CNCC中的BMP信号如何调节 颅面软骨形成。 在我们的初步研究中，我们采用了在BMP中控制BMP信号传导的Cre-LoxP系统， 受体特异性的方式。据报道，在细胞因子中的功能获得性突变， BMP轴导致人类颅面异常。根据这一观察，我们以前 报道了通过BMPR 1A，BMP I型受体之一， 由于颅缝中的异位软骨形成而导致颅缝早闭。在本提案中，我们重点关注 另一种BMP I型受体ACVR 1。CNCC中通过ACVR 1增强BMP信号传导的胚胎 （以下称为“ACVR 1突变体”）显示颌骨畸形和唇裂，这是不同的颅面畸形。 BMPR 1A突变体的表型。有趣的是，ACVR 1突变体显示出增强的软骨 Sox 9是软骨形成的关键转录因子，初步 筛选显示，哺乳动物雷帕霉素靶蛋白（mTOR）的水平在哺乳动物中显著升高， ACVR 1突变体。重要的是，雷帕霉素对mTOR信号的抑制拯救了颅面软骨。 ACVR 1突变体中的畸形，表明由BMP增强触发的mTOR信号传导是 负责增强的软骨内骨化。值得注意的是，以微管为基础的初级纤毛 在ACVR 1突变体中，CNCC衍生的软骨细胞中富含触角样细胞器， 睫状蛋白的抑制挽救了ACVR 1突变体的颅面软骨异常。这些 结果表明，ACVR 1突变体中的初级纤毛是软骨增强的病因 脸上的成长。我们的中心假设是BMP信号通过CNCC中的ACVR 1调节 mTOR，其是颅面软骨发育期间初级纤毛形成所需的。我们将测试 我们的假设通过追求特定的目标（1）研究CNCC中BMP信号如何调节原发性 软骨形成过程中纤毛的形成，以及（2）研究BMP-mTOR-纤毛轴如何支配 面部发育过程中的软骨形成。 我们的研究将揭示CNCC中BMP-mTOR-初级纤毛新轴的分子细节， 是颅面软骨形成的关键

PROJECT SUMMARY Craniofacial abnormalities are largely attributed to defects in the formation, migration and differentiation of cranial neural crest cells (CNCCs). Since CNCCs are developmentally plastic, understanding the genetic and molecular pathways controlling the specification of chondrocyte and osteoblast lineages from CNCC is a prerequisite for interpreting the etiology of craniofacial skeletal disorders. After the discovery of bone morphogenetic proteins (BMPs), many elegant studies have revealed their significant role in skeletal development. However, it is still unclear why BMPs are capable of changing the fate and lineage of undifferentiated stem cells of CNCCs toward skeletogenic cells. Especially, despite the importance of BMPs during craniofacial bone development, it is poorly understood how BMP signaling in CNCCs regulates craniofacial cartilage formation. In our preliminary studies, we employed the Cre-LoxP system that controls BMP signaling in a BMP receptor-specific manner in the mouse. It has been reported that gain-of-function mutations in components of the BMP axis cause craniofacial abnormalities in humans. Consistent with this observation, we previously reported that augmentation of BMP signaling in CNCCs through BMPR1A, one of the BMP type I receptors, causes craniosynostosis due to ectopic cartilage formation in cranial sutures. In this proposal, we focus on another BMP type I receptor, ACVR1. Embryos with augmented BMP signaling through ACVR1 in CNCCs (“ACVR1 mutants” hereafter) displayed jaw malformation and cleft lip, which are distinct craniofacial phenotypes from those of BMPR1A mutants. Interestingly, ACVR1 mutants displayed the enhanced cartilage growth in the face with upregulation of Sox9, a key transcription factor for chondrogenesis. Preliminary screenings revealed that the levels of mammalian target of rapamycin (mTOR) were significantly elevated in ACVR1 mutants. Importantly, inhibition of mTOR signaling by rapamycin rescued the craniofacial cartilage malformation in ACVR1 mutants, indicating that mTOR signaling triggered by the augmentation of BMP is responsible for the enhanced endochondral ossification. Of note, primary cilia, which are microtubule-based antenna-like organelles, were enriched in CNCC-derived chondrocytes in ACVR1 mutants, and the suppression of a ciliary protein rescued the craniofacial cartilage abnormalities in ACVR1 mutants. These results suggest that primary cilia in ACVR1 mutants are responsible for the etiology of enhanced cartilage growth in the face. Our central hypothesis here is that BMP signaling through ACVR1 in CNCCs regulates mTOR, which is required for primary cilium formation during craniofacial cartilage development. We will test our hypothesis by pursuing the specific aims (1) To examine how BMP signaling in CNCCs regulates primary cilium formation during chondrogenesis, and (2) To examine how BMP-mTOR-cilia axis governs chondrogenesis during facial development. Our study will uncover the molecular details of how the novel axis of BMP-mTOR-primary cilia in CNCCs is critical for craniofacial cartilage formation.