Reginato A M, Tuan R S, Ono T, Jimenez S A, Jacenko O
Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Dev Dyn. 1993 Dec;198(4):284-95. doi: 10.1002/aja.1001980406.
Maintenance of chick embryos in long-term culture without their calcareous egg-shell is a useful method for studying the relationship between calcium homeostasis and cell differentiation during skeletogenesis. Previously, we have shown that in shell-less (SL) embryos, calcium deficiency induces a cartilage-like phenotype in osteogenic tissues, such as calvaria (Jacenko and Tuan [1986] Dev. Biol. 115:215). In this investigation, we have studied the relationship between cartilage calcification and hypertrophy, and the expression of type X collagen, a specific product of hypertrophic chondrocytes. For this study, the cephalic (calcifying) and caudal (permanently cartilaginous) regions of sterna from day 18 and day 20 normal (NL) and SL embryos were metabolically labeled with [14C]-proline. Analysis of the biosynthetic products revealed significant differences in type X collagen expression in the cephalic region of sternal cartilage. In NL tissues, type X collagen production increased from 13.1% of total collagen at day 18 to 43.7% at day 20. In contrast, in SL embryos, type X collagen was not detectable until day 20, when it represented only 1% of total collagen. Comparison of the NL and SL embryos with respect to their serum calcium level and sternal calcium content and histology revealed a direct relationship between low systemic calcium and limited cartilage hypertrophy, undermineralization, and decreased type X collagen production in the sternal cephalic cartilage. Supplementation of CaCO3 to SL embryos increased their serum and sternal calcium, and restored cartilage hypertrophy, mineralization, and type X collagen synthesis in the cephalic portion of the sterna. These findings confirm that a critical relationship exists between calcium homeostasis, chondrocyte hypertrophy, mineralization, and type X collagen synthesis in the cephalic region of sternal cartilage. These results further demonstrate the importance of calcium in the morphogenetic events of endochondral ossification, in particular the transition from hyaline cartilage to hypertrophic cartilage, and eventually to bone.
在无钙质蛋壳的情况下对鸡胚胎进行长期培养，是研究骨骼发生过程中钙稳态与细胞分化之间关系的一种有用方法。此前，我们已经表明，在无壳（SL）胚胎中，钙缺乏会在成骨组织（如颅骨）中诱导出软骨样表型（雅琴科和段 [1986] 《发育生物学》115:215）。在本研究中，我们研究了软骨钙化与肥大之间的关系，以及X型胶原（肥大软骨细胞的一种特异性产物）的表达。为了进行这项研究，对第18天和第20天正常（NL）和SL胚胎胸骨的头部（钙化）和尾部（永久软骨）区域用[14C] - 脯氨酸进行代谢标记。对生物合成产物的分析显示，胸骨软骨头部区域X型胶原表达存在显著差异。在NL组织中，X型胶原的产生从第18天占总胶原的13.1%增加到第20天的43.7%。相比之下，在SL胚胎中，直到第20天才能检测到X型胶原，此时它仅占总胶原的1%。对NL和SL胚胎的血清钙水平、胸骨钙含量和组织学进行比较，发现全身低钙与胸骨头部软骨的有限软骨肥大、矿化不足以及X型胶原产生减少之间存在直接关系。向SL胚胎补充碳酸钙可提高其血清和胸骨钙水平，并恢复胸骨头部的软骨肥大、矿化以及X型胶原合成。这些发现证实，胸骨软骨头部区域的钙稳态、软骨细胞肥大、矿化和X型胶原合成之间存在关键关系。这些结果进一步证明了钙在软骨内成骨的形态发生事件中的重要性，特别是从透明软骨向肥大软骨，最终向骨的转变。
