Nalin A M, Greenlee T K, Sandell L J
Department of Orthopaedics, University of Washington, Seattle 98108, USA.
Dev Dyn. 1995 Jul;203(3):352-62. doi: 10.1002/aja.1002030307.
The developmental sequence of the embryonic joint has been well studied morphologically. There are, however, no definitive studies of cell function during joint development. In order to begin to understand the differentiation events that contribute to joint formation, we examined the expression of collagen mRNAs encoding types I, IIA, IIB, and XI. In situ hybridization was performed on chicken embryo hind limb buds and digits from day 7 to day 18 (Hamburger and Hamilton stages 31-44). In the day 7 (stage 31) limb bud, there was a condensation of mesenchyme forming the primitive tarsal and metatarsal bones that showed abundant expression of type IIA procollagen message, but no type IIB or type alpha 1(XI) message. By day 8 (stage 33), co-expression of types IIA, and type XI procollagen mRNAs was observed in the condensations, with expression of IIB restricted to early chondrocytes with metachromatically staining matrix. At this stage, DNA fragmentation characteristic of apoptosis was observed in cells near the midline of the interzone region between the developing anlagen, and in areas between and around the individual digits of the paddle. The presumptive apoptotic cells were more numerous at day 9 (stage 35), and were not found in the developing joint at subsequent time points, including the initiation of spatial cavitation of the joint. From days 11-18, type IIA procollagen mRNA was expressed in flattened cells at the surface of the anlagen, and in the perichondrium and in the developing joint capsule; type IIB mRNA message was found only in chondrocytes. Type XI mRNA was expressed by all type II-expressing cells. Alpha 1(I) mRNA was expressed early by cells of the interzone and capsule, but as cavitation progressed, the type I expressing cells of the interzone merged with the superficial layer of the articular surface. Thus, at the time of joint cavitation, there was a distinct pattern of expression of procollagen messages at the articular surface, with type I being outermost, followed by morphologically similar cells expressing type IIA, then chondrocytes expressing type IIB. The progenitor cells expressing type IIA message define a new population of cells. These cell populations contribute to the molecular heterogeneity of the articular cartilage, and these same populations likely exist in the developing joints of other species. The transient transcription of type II and type XI collagen genes, characteristic of chondrocytes, by cells in the joint capsule demonstrates that these cells may have chondrogenic potential.
胚胎关节的发育序列已在形态学上得到充分研究。然而，对于关节发育过程中的细胞功能尚无确定性研究。为了开始理解促成关节形成的分化事件，我们检测了编码I型、IIA型、IIB型和XI型胶原蛋白的mRNA的表达情况。对第7天至第18天（Hamburger和Hamilton分期31 - 44期）的鸡胚后肢芽和趾进行原位杂交。在第7天（31期）的肢芽中，间充质发生凝聚形成原始跗骨和跖骨，其显示出丰富的IIA型前胶原蛋白信息表达，但没有IIB型或α1(XI)型信息表达。到第8天（33期），在凝聚物中观察到IIA型和XI型前胶原蛋白mRNA的共表达，而IIB型的表达局限于具有异染性染色基质的早期软骨细胞。在此阶段，在发育中的原基之间的中间区域中线附近的细胞以及桨状结构中各个趾之间和周围的区域中观察到凋亡特征性的DNA片段化。推测的凋亡细胞在第9天（35期）更多，并且在随后的时间点，包括关节开始出现空间空化时，在发育中的关节中未发现。从第11天到第18天，IIA型前胶原蛋白mRNA在原基表面的扁平细胞、软骨膜和发育中的关节囊中表达；IIB型mRNA仅在软骨细胞中发现。XI型mRNA由所有表达II型的细胞表达。α1(I)型mRNA在中间区域和关节囊的细胞中早期表达，但随着空化进展，中间区域表达I型的细胞与关节表面的表层融合。因此，在关节空化时，关节表面存在前胶原蛋白信息的独特表达模式，I型在最外层，其次是表达IIA型的形态相似细胞，然后是表达IIB型的软骨细胞。表达IIA型信息的祖细胞定义了一个新的细胞群体。这些细胞群体促成了关节软骨的分子异质性，并且这些相同的群体可能存在于其他物种的发育关节中。关节囊中细胞对软骨细胞特有的II型和XI型胶原蛋白基因的瞬时转录表明这些细胞可能具有软骨形成潜能。
