Department of Oral and Maxillofacial Reconstructive Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan.
The first department of Oral and Maxillofacial Surgery, Osaka University Graduate School of Dentistry, Osaka, Japan.
J Dent Res. 2023 Oct;102(11):1241-1251. doi: 10.1177/00220345231184405. Epub 2023 Aug 14.
Cranial base synchondroses are the endochondral ossification centers for cranial base growth and thus indispensable for proper skull, brain, and midfacial development. The synchondroses are composed of mirror-image growth plates that are continuously maintained from the embryonic to postnatal stage through chondrocyte differentiation. Several factors, including Pth1r signaling, are known to control fetal synchondrosis development. However, there are currently no reports regarding any role for Pth1r signaling in postnatal cranial base and synchondrosis development. Also, the mesenchymal cells that source Pth1r signaling for synchondroses are not known. Here, we employed an inducible mouse model, a hedgehog-responsive driver, focusing on the postnatal study. We performed 2 inducible protocols using mice that uncovered distinct patterning of Gli1-positive and Gli1-negative chondrocytes in the synchondrosis cartilage. Moreover, we generated mice to assess their functions in postnatal synchondrosis and found that the mutants had survived postnatally. The mutant skulls morphologically presented unambiguous phenotypes where we noticed the shortened cranial base and premature synchondrosis closure. Histologically, gradual disorganization in mutant synchondroses caused an uncommon remaining central zone between hypertrophic zones on both sides while the successive differentiation of round, flat, and hypertrophic chondrocytes was observed in control sections. These mutant synchondroses disappeared and were finally replaced by bone. Of note, the mutant fusing synchondroses lost their characteristic patterning of Gli1-positive and Gli1-negative chondrocytes, suggesting that loss of Pth1r signaling alters the distribution of hedgehog-responsive chondrocytes. Moreover, we performed laser microdissection and RNA sequencing to characterize the flat proliferative and round resting chondrocytes where we found flat chondrocytes have a characteristic feature of both chondrocyte proliferation and maturation. Taken together, these data demonstrate that Pth1r signaling in Gli1-positive cells is essential for postnatal development and maintenance in cranial base synchondroses. Our findings will elucidate previously unknown aspects of Pth1r functions in cranial biology and development.
颅底骺软骨是颅底生长的软骨内骨化中心，对于颅骨、大脑和中面部的正常发育是必不可少的。骺软骨由镜像生长板组成，通过软骨细胞分化，从胚胎期到出生后阶段持续维持。已知包括 Pth1r 信号在内的几种因素控制胎儿骺软骨的发育。然而，目前尚无关于 Pth1r 信号在出生后颅底和骺软骨发育中的作用的报道。此外，作为骺软骨来源的 Pth1r 信号的间充质细胞也不清楚。在这里，我们利用诱导型小鼠模型，一种 hedgehog 反应性驱动，聚焦于出生后的研究。我们使用 小鼠进行了 2 种诱导实验方案，揭示了骺软骨软骨中 Gli1 阳性和 Gli1 阴性软骨细胞的不同模式。此外，我们生成了 小鼠来评估它们在出生后骺软骨中的功能，发现突变体在出生后存活下来。突变体颅骨在形态上表现出明确的表型，我们注意到颅底缩短和骺软骨过早闭合。组织学上，突变骺软骨逐渐出现组织紊乱，导致两侧肥大区之间出现异常的中央区残留，而在对照切片中观察到圆形、扁平、肥大软骨细胞的连续分化。这些突变骺软骨消失，最终被骨取代。值得注意的是，融合骺软骨的突变体失去了 Gli1 阳性和 Gli1 阴性软骨细胞的特征性模式，表明 Pth1r 信号的丧失改变了 hedgehog 反应性软骨细胞的分布。此外，我们进行了激光显微切割和 RNA 测序，以表征扁平增殖和圆形静止软骨细胞，我们发现扁平软骨细胞具有软骨细胞增殖和成熟的特征。综上所述，这些数据表明，Gli1 阳性细胞中的 Pth1r 信号对于颅底骺软骨的出生后发育和维持是必不可少的。我们的研究结果将阐明 Pth1r 在颅生物学和发育中的以前未知的功能方面。
