Fang J, Hall B K
Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
Int J Dev Biol. 1995 Jun;39(3):519-28.
Progenitor cells in the periosteum-perichondrium of the posterior hook of the quadratojugal (QJ, a membrane bone) in the embryonic chick are bipotential for osteogenesis and chondrogenesis. These cells switch from osteogenesis to chondrogenesis between 10 to 11 days in normal (mobile) embryos but not in paralyzed (immobile) embryos. Expression of neural cell adhesion molecule (NCAM) was studied using a monoclonal antibody in QJ hooks from normal and paralyzed chick embryos between 10 and 21 days of incubation. NCAM is expressed in osteoprogenitor cells and osteoblasts but not in chondroprogenitor cells, chondroblasts, or chondrocytes. The switch of progenitor cell differentiation from an osteogenic to a chondrogenic pathway between 10 and 11 days of incubation coincides with down-regulation of NCAM expression. Both initiation of secondary chondrogenesis and down-regulation of NCAM depend on biomechanical stimulation. In embryos paralyzed at 9 days, secondary cartilage fails to form and progenitor cells remain positive for NCAM. Furthermore, paralysis influences NCAM expression in progenitor cells before secondary chondrogenesis morphologically begins, indicating that NCAM may play a role in the initiation of secondary chondrogenesis. In 15-day normal embryos, NCAM-positive cells accumulate between the perichondrium and secondary cartilage in a position that prevents further cartilage formation in the hook. In 19-day embryos, these cells lose their NCAM expression and restart chondrogenesis in a second phase of differentiation, forming an articular cartilage. Loss of NCAM expression in this cell layer and re-commencement of chondrogenesis do not occur in embryos paralyzed at 13 days, and therefore also require biomechanical stimulation. Hence, down-regulation of NCAM expression correlates with two phases of secondary chondrogenesis in embryonic life, both of which are dependent upon embryonic movement.
胚胎期鸡方轭骨（QJ，一种膜性骨）后钩的骨膜 - 软骨膜中的祖细胞具有成骨和软骨形成的双潜能。在正常（可活动）胚胎中，这些细胞在10至11天之间从成骨转变为软骨形成，但在瘫痪（不能活动）的胚胎中则不会。使用单克隆抗体研究了孵化10至21天的正常和瘫痪鸡胚胎的QJ钩中神经细胞黏附分子（NCAM）的表达。NCAM在骨祖细胞和成骨细胞中表达，但在软骨祖细胞、软骨细胞和成软骨细胞中不表达。孵化10至11天之间祖细胞分化从成骨途径转变为软骨形成途径与NCAM表达的下调同时发生。继发性软骨形成的起始和NCAM的下调均依赖于生物力学刺激。在9天瘫痪的胚胎中，继发性软骨未能形成，祖细胞对NCAM仍呈阳性。此外，在继发性软骨形成在形态学上开始之前，瘫痪会影响祖细胞中NCAM的表达，表明NCAM可能在继发性软骨形成起始中发挥作用。在15天的正常胚胎中，NCAM阳性细胞在软骨膜和继发性软骨之间积聚，其位置阻止了钩中进一步的软骨形成。在19天的胚胎中，这些细胞失去NCAM表达，并在分化的第二阶段重新开始软骨形成，形成关节软骨。在13天瘫痪的胚胎中，该细胞层中不会发生NCAM表达的丧失和软骨形成的重新开始，因此这也需要生物力学刺激。因此，NCAM表达的下调与胚胎期继发性软骨形成的两个阶段相关，这两个阶段均依赖于胚胎运动。
