Unraveling the Cellular Dynamics of the Cranial Base Synchondroses Throughout Postnatal Craniofacial Development

颅底生长中心软骨结合是调节出生后颅面双向运动的必要条件 通过形成上鼻气道的结构基础， 咀嚼复合体与长骨生长板相似，软骨结合中的软骨细胞也是有组织的 进入静止、增殖和肥大区，在骨骼成熟过程中骨化。重要的是，组织 并且需要增殖软骨细胞的活化来促进颅底生长。成纤维细胞生长因子 受体3（Fgfr 3）在软骨结合的软骨细胞中表达，Fgfr 3功能获得性突变导致 软骨发育不全伴软骨结合过早融合和人类面中部发育不全， 小鼠目前面中部发育不良的治疗仅限于颅面和正颌重建 病人的手术。尽管这些临床上有意义的发现，但Fgfr 3+软骨细胞的行为尚不清楚 整个出生后软骨结合的生长。因此，本提案的总体目标是确定机制 Fgfr 3+增殖软骨细胞通过其协调出生后软骨结合生长和成熟。我 初步数据表明，锁骨颅骨发育不良的致病基因的条件性缺失， 转录因子2（Runx2），在小鼠的Fgfr 3+软骨细胞中引起软骨结合的过早融合， 加速软骨细胞肥大和减少成骨细胞形成。虽然Runx2作为一个核心的角色， 成骨细胞分化和骨骼形成的调节因子已经在长骨中建立，其在 软骨结合的发展仍不清楚。通过结合我们目前对Fgfr 3相关颅 根据我广泛的初步数据，我假设表达Fgfr 3的软骨细胞 维持出生后颅底软骨结合的双向定向和生长潜力 通过一种依赖于Runx2激活的机制。 提出了两个目标来解决中心假设。1.评估克隆动态和细胞 软骨结合中Fgfr 3+软骨细胞的异质性。2.确定Runx2对Fgfr 3+软骨细胞的作用 软骨结合中的组织。该项目旨在提供新的机制洞察产后 软骨结合的生长和成熟，从而推进目前的科学状态的颅底生物学。 此外，这些调查旨在揭示将Runx2作为中央调节器的创新机制 出生后软骨结合的发展。值得注意的是，该项目旨在促进未来的研究， 畸形软骨结合患者中治疗靶向Fgfr 3相关途径突变。

The cranial base growth center synchondroses are essential for regulating bidirectional postnatal craniofacial growth and skeletal patterning of the midface by forming the structural foundation for the upper nasal airway and masticatory complex. Similar to the long bone growth plate, chondrocytes in the synchondroses are organized into resting, proliferating and hypertrophic zones that ossify during skeletal maturation. Importantly, organization and activation of proliferating chondrocytes is required to promote cranial base growth. Fibroblast growth factor receptor 3 (Fgfr3) is expressed in chondrocytes in the synchondroses and Fgfr3 gain-of-function mutations cause achondroplasia associated with premature fusion of the synchondroses and midfacial hypoplasia in humans and mice. Current treatments for midfacial hypoplasia are limited to craniofacial and orthognathic reconstructive surgeries in patients. Despite these clinically meaningful findings, it is unknown how Fgfr3+ chondrocytes behave throughout postnatal synchondrosis growth. Therefore, the overall goal of this proposal is to identify mechanisms by which Fgfr3+ proliferating chondrocytes orchestrate postnatal synchondrosis growth and maturation. My preliminary data suggests that conditional deletion of the causative gene for cleidocranial dysplasia, runt-related transcription factor 2 (Runx2), in Fgfr3+ chondrocytes in mice causes premature fusion of the synchondroses, accelerated chondrocyte hypertrophy and decreased osteoblast formation. Although Runx2’s role as a central regulator of osteoblast differentiation and skeletal formation has been established in long bones, its function in synchondrosis development remains unknown. By combining our current knowledge of Fgfr3-related cranial base malformations with my extensive preliminary data, I hypothesize that Fgfr3-expressing chondrocytes maintain the bidirectional orientation and growth potential of the postnatal cranial base synchondroses through a mechanism dependent on Runx2 activation. Two aims are proposed to address the central hypothesis. 1. Assess the clonal dynamics and cellular heterogeneity of Fgfr3+ chondrocytes in the synchondroses. 2. Define the role of Runx2 on Fgfr3+ chondrocyte organization in the synchondroses. This project seeks to provide novel mechanistic insight into postnatal synchondrosis growth and maturation, thereby advancing the current scientific state of cranial base biology. Furthermore, these investigations aim to unravel an innovative mechanism placing Runx2 as a central regulator of postnatal synchondrosis development. Notably, this project intends to catalyze future studies into therapeutically targetable Fgfr3-related pathways mutated in patients with malformed synchondroses.