The role of BMP signaling in craniofacial cartilage development

项目总结 颅面畸形在很大程度上归因于肿瘤的形成、迁移和分化过程中的缺陷。 脑神经脊细胞(CNCCs)。由于CNCC在发育过程中是可塑性的，因此理解遗传和 控制CNCC软骨细胞和成骨细胞系特性的分子途径是一种 解释头面部骨骼疾病病因学的先决条件。在发现了骨头之后 形态发生蛋白(BMP)，许多优雅的研究揭示了它们在骨骼中的重要作用 发展。然而，目前仍不清楚为什么BMP能够改变人的命运和血统 未分化的CNCCs干细胞向骨源性细胞分化。尤其是，尽管BMP很重要 在颅面骨发育过程中，BMP信号在CNCC中是如何调节的还知之甚少。 颅面软骨形成。 在我们的初步研究中，我们使用了CRE-loxP系统来控制BMP中的BMP信号 受体在小鼠中的特异性方式。已有报道称，功能增益突变的成分 BMP轴会导致人类的头面部畸形。与这一观察结果一致，我们之前 报道通过BMP I型受体之一的BMPR1A增强CNCC中的BMP信号。 由于颅缝中异位软骨的形成而导致颅骨融合。在这份提案中，我们重点关注 另一种BMP I型受体，ACVR1。在CNCCs中通过ACVR1增强BMP信号的胚胎 (以下简称ACVR1突变体)表现为颌骨畸形和唇裂，与颅面部特征不同 BMPR1A突变体的表型。有趣的是，ACVR1突变体显示出增强的软骨 面部生长与软骨形成的关键转录因子Sox9上调有关。初步 筛查显示，哺乳动物雷帕霉素靶标(MTOR)水平在 ACVR1突变体。重要的是，雷帕霉素抑制mTOR信号转导挽救了颅面软骨 ACVR1突变体中的畸形，表明BMP增强触发的mTOR信号是 是软骨内骨化增强的原因。值得注意的是，初级纤毛以微管为基础 在ACVR1突变体中，CNCC来源的软骨细胞中富含触角状细胞器，并且 一种纤毛蛋白的抑制挽救了ACVR1突变体的头面部软骨异常。这些 结果提示ACVR1突变体的初级纤毛与软骨增厚的病因有关。 脸部的生长。我们的中心假设是CNCC中通过ACVR1的BMP信号调节 MTOR，这是头面部软骨发育过程中初级纤毛形成所必需的。我们将测试 我们的假设是通过追求特定的目标(1)检查CNCC中的BMP信号如何调节初级 软骨形成过程中纤毛的形成；(2)观察BMP-mTOR-纤毛轴如何调控 面部发育过程中的软骨生成。 我们的研究将揭示CNCC中BMP-mTOR-初级纤毛轴的分子细节 对头面部软骨的形成至关重要。

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.