Type II collagen-positive (Col2⁺) cells have been reported as skeletal stem cells (SSCs), but the contribution of Col2⁺ progenitors to skeletal development both prenatally and postnatally during aging remains unclear. To address this question, we generated new mouse models with ablation of Col2⁺ cells at either the embryonic or postnatal stages. The embryonic ablation of Col2⁺ progenitors resulted in the death of newborn mice due to a decrease in skeletal blood vessels, loss of all vertebral bones and absence of most other bones except part of the craniofacial bone, the clavicle bone and a small piece of the long bone and ribs, which suggested that intramembranous ossification is involved in long bone development but does not participate in spine development. The postnatal ablation of Col2⁺ cells resulted in mouse growth retardation and a collagenopathy phenotype. Lineage tracing experiments with embryonic or postnatal mice revealed that Col2⁺ progenitors occurred predominantly in the growth plate (GP) and articular cartilage, but a limited number of Col2⁺ cells were detected in the bone marrow. Moreover, the number and differentiation ability of Col2⁺ progenitors in the long bone and knee joints decreased with increasing age. The fate-mapping study further revealed Col2⁺ lineage cells contributed to, in addition to osteoblasts and chondrocytes, CD31⁺ blood vessels in both the calvarial bone and long bone. Specifically, almost all blood vessels in calvarial bone and 25.4% of blood vessels in long bone were Col2⁺ lineage cells. However, during fracture healing, 95.5% of CD31⁺ blood vessels in long bone were Col2⁺ lineage cells. In vitro studies further confirmed that Col2⁺ progenitors from calvarial bone and GP could form CD31⁺ vascular lumens. Thus, this study provides the first demonstration that intramembranous ossification is involved in long bone and rib development but not spine development. Col2⁺ progenitors contribute to CD31⁺ skeletal blood vessel formation, but the percentage differs between long bone and skull bone. The number and differentiation ability of Col2⁺ progenitors decreases with increasing age.

II 型胶原蛋白阳性 (Col2 ⁺ ) 细胞已被报道为骨骼干细胞 (SSC)，但 Col2 ⁺祖细胞在衰老过程中对产前和产后骨骼发育的贡献仍不清楚。为了解决这个问题，我们通过在胚胎或出生后阶段消融 Col2 ⁺细胞来生成新的小鼠模型。 Col2 ⁺祖细胞的胚胎消融导致新生小鼠死亡，原因是骨骼血管减少，所有椎骨丢失，除了部分颅面骨、锁骨和一小块颅骨外，大多数其他骨骼缺失。长骨和肋骨，这表明膜内骨化参与长骨发育，但不参与脊柱发育。 Col2 ⁺细胞的出生后消融导致小鼠生长迟缓和胶原病表型。对胚胎或出生后小鼠的谱系追踪实验表明，Col2 ⁺祖细胞主要出现在生长板（GP）和关节软骨中，但在骨髓中检测到有限数量的 Col2 ⁺细胞。此外，长骨和膝关节中Col2 ⁺祖细胞的数量和分化能力随着年龄的增长而下降。命运图谱研究进一步揭示，除了成骨细胞和软骨细胞外，Col2 ⁺谱系细胞还促成颅骨和长骨中的 CD31 ⁺血管。具体来说，颅骨中几乎所有血管和长骨中25.4%的血管都是Col2 ⁺谱系细胞。然而，在骨折愈合过程中，95.长骨中 5% 的 CD31 ⁺血管是 Col2 ⁺谱系细胞。体外研究进一步证实来自颅骨和GP的Col2 ⁺祖细胞可以形成CD31 ⁺血管腔。因此，这项研究首次证明膜内骨化参与长骨和肋骨发育，但不参与脊柱发育。 Col2 ⁺祖细胞有助于 CD31 ⁺骨骼血管的形成，但长骨和颅骨之间的百分比不同。 Col2 ⁺祖细胞的数量和分化能力随着年龄的增长而降低。