Although recent lineage studies strongly support a chondrocyte-to-osteoblast differentiation continuum, the biological significance and molecular basis remain undetermined. In silico analysis at a single-cell level indicates a transient shutdown of Hedgehog-related transcriptome during simulated cartilage-to-bone transition. Prompted by this, we genetically induce gain- and loss-of function to probe the role of Hedgehog signaling in cartilage-to-bone transition. Ablating Smo in hypertrophic chondrocytes (HCs) does not result in any phenotypic outcome, whereas deleting Ptch1 in HCs leads to disrupted formation of primary spongiosa and actively proliferating HCs-derived osteogenic cells that contribute to bony bulges seen in adult mutant mice. In HCs-derived osteoblasts, constitutive activation of Hedgehog signaling blocks their further differentiation to osteocytes. Moreover, ablation of both Smo and Ptch1 in HCs reverses neither persistent Hedgehog signaling nor bone overgrowths. These results establish a functional contribution of extended chondrocyte lineage to bone homeostasis and diseases, governed by an unanticipated mode of regulation for Hedgehog signaling independently of Smo.

尽管最近的谱系研究强烈支持软骨细胞到成骨细胞分化的连续性，但其生物学意义和分子基础仍未确定。单细胞水平的计算机分析表明，在模拟软骨到骨骼的转变过程中，Hedgehog 相关转录组暂时关闭。受此提示，我们通过基因诱导功能的获得和丧失，以探索 Hedgehog 信号传导在软骨到骨转变中的作用。消融肥大软骨细胞 ( HCs ) 中的Smo不会导致任何表型结果，而删除Ptch1在 HCs 中，会破坏原发性海绵体的形成，并积极增殖 HCs 衍生的成骨细胞，这些成骨细胞有助于成年突变小鼠中出现的骨隆起。在 HCs 衍生的成骨细胞中，Hedgehog 信号传导的组成性激活阻止了它们进一步分化为骨细胞。此外， HCs 中Smo和Ptch1的消融既不会逆转持续的 Hedgehog 信号传导，也不会逆转骨过度生长。这些结果确定了扩展的软骨细胞谱系对骨稳态和疾病的功能贡献，由独立于 Smo 的 Hedgehog 信号传导的意外调节模式控制。