Type X collagen gene expression during formation of primary bone marrow in the endochondral bone

X型胶原蛋白由生长板的肥大软骨细胞合成并沉积在钙化区域，而II型胶原蛋白由静止和增殖的软骨细胞合成。我们检查了经历软骨内骨化的胚胎鸡椎骨中 I 型、II 型和 X 型胶原蛋白 mRNA 的时空定位，并利用原位杂交证明了鸡骨膜同种异体移植诱导的异位软骨内骨中 X 型胶原蛋白基因的非典型表达。在第 45 阶段的胚胎鸡椎骨中，在成熟的软骨细胞区域中注意到 II 型胶原蛋白和 X 型 mRNA 之间的分布模式相反。 I 型胶原蛋白 mRNA 的高信号仅限于源自骨膜间充质细胞的成骨细胞。原代骨髓在 X 型胶原蛋白沉积的区域迅速发育。另一方面，在皮下移植骨膜的异位软骨内骨中观察到这些胶原mRNA的不同表达。移植后五天，在非典型软骨块中鉴定出发育中的非肥大软骨细胞，其快速表达 X 型胶原蛋白 mRNA。移植后第9天，在类骨质和/或编织骨中显示出稀疏分布的具有高信号x型胶原mRNA的软骨细胞。来自未分化骨膜间充质细胞的X型胶原基因快速表达的软骨细胞表型似乎参与了初级骨髓形成和骨折修复的早期阶段。

Type X collagen is synthesized by hypertrophic chondrocytes of the growth plate and deposited in the calcifying region, while type II collagen is synthesized by resting and proliferating chondrocytes. We examined the spatiotemporal localization of collagen type I, II and X mRNAs in embryonic chick vertebrae undergoing endochondral ossification, and also demonstrated an atypical expression of collagen type X gene in the heterotopic endochondral bone induced by chick periosteal allografts using in situ hybridization. In the embryonic chick vertebra a stage 45, a reversed pattern of distribution between collagen type II and type X mRNAs was noted in maturing chondrocyte zones. High signals of collagen type I mRNA were restricted in osteoblasts derived from periosteal mesenchymal cells. Primary bone marrow rapidly developed in the area in which type X collagen was deposited. On the other hand, different expressions of these collagen mRNAs were observed in the heterotopic endochondral bone of the subcutaneously grafted periosteum. Five days after transplantation, developing non-hypertrophic chondrocytes with rapid expression of collagen type X mRNA were identified in the mass of atypical cartilage. At day 9 after transplantation, sparsely distributed chondrocytes having high signals of collagen type x mRNA were demonstrated in osteoid and/or woven bone.The phenotype of chondrocyte showing rapid expression of collagen type X gene derived from undifferentiated periosteal mesenchymal cells seems to participate in the primary bone marrow formation and in the early stage of fracture repair.