Reduced amounts of cartilage collagen fibrils and growth plate anomalies in transgenic mice harboring a glycine-to-cysteine mutation in the mouse type II procollagen alpha 1-chain gene.

We have generated transgenic mice harboring a glycine-to-cysteine mutation in residue 85 of the triple helical domain of mouse type II collagen. The offspring of different founders displayed a phenotype of severe chondrodysplasia characterized by short limbs and trunk, cranio-facial deformities, and cleft palate. The affected pups died of acute respiratory distress caused by an inability to inflate lungs at birth. Staining of the skeleton showed a severe retardation of growth for practically all bones. Light microscopic examination indicated a decrease in cartilage matrix density, a severe disorganization of growth plate architecture, and the presence of streaks of fibrillar material in the cartilage matrix. Electron microscopic analysis showed a pronounced decrease in the number of typical thin cartilage collagen fibrils, distension of the rough endoplasmic reticulum of chondrocytes, and the presence of abnormally large banded collagen fibril bundles. The level of expression of the mutant type II procollagen alpha 1 chain transgene in cartilage tissues was approximately equal to that of the endogenous gene in two of the strains. We propose that the principal consequence of the mutation is a considerable reduction in density of the typical thin cartilage collagen fibrils and that this phenomenon causes the severe disorganization of the growth plate. We also postulate that the abnormal thick collagen fibrils are probably related to a defect in crosslinking between the collagen molecules. The cartilage anomalies displayed by these transgenic mice are remarkably similar to those of certain human chondrodysplasias. IMAGES:

本研究构建了携带小鼠II型胶原（mouse type II collagen）三螺旋结构域第85位残基甘氨酸至半胱氨酸突变的转基因小鼠（transgenic mice）。不同创始株的后代表现出严重软骨发育不良（chondrodysplasia）表型，特征为肢体与躯干短小、颅面畸形及腭裂。患病幼鼠因出生时无法扩张肺部引发急性呼吸窘迫而死亡。骨骼染色结果显示，几乎所有骨骼均出现严重生长迟缓。光学显微镜检查（light microscopic examination）可见软骨基质密度（cartilage matrix density）降低、生长板结构（growth plate architecture）严重紊乱，且软骨基质中存在纤维状物质条带。电子显微镜分析（electron microscopic analysis）显示，典型的细软骨胶原原纤维数量显著减少，软骨细胞（chondrocytes）的粗面内质网（rough endoplasmic reticulum）扩张，同时存在异常粗大的带型胶原原纤维束（banded collagen fibril bundles）。在两个品系的软骨组织中，突变型II型前胶原α1链转基因（mutant type II procollagen alpha 1 chain transgene）的表达水平与内源基因（endogenous gene）大致相当。本研究提出，该突变的主要后果是典型细软骨胶原原纤维的密度大幅降低，这一现象导致生长板结构严重紊乱。此外，我们推测异常粗大的胶原原纤维可能与胶原分子间的交联（crosslinking）缺陷相关。这些转基因小鼠表现出的软骨异常与某些人类软骨发育不良（human chondrodysplasias）极为相似。图像：