The gene expression and protein synthesis of small leucine-rich proteoglycans (SLRPs), including decorin, biglycan, fibromodulin, and lumican, was analyzed in the context of the hypothesis that they are closely related to tooth formation. In situ hybridization, immunohistochemistry, and organ culture with metabolic labeling of [35S] were carried out in mouse first molar tooth germs of different developmental stages using ICR mice at embryonic day (E) 13.5 to postnatal day (P) 7.0. At the bud and cap stage, decorin mRNA was expressed only in the surrounding mesenchyme, but not within the tooth germ. Biglycan mRNA was then expressed in the condensing mesenchyme and the dental papilla of the tooth germ. At the apposition stage (late bell stage), both decorin and biglycan mRNA were expressed in odontoblasts, resulting in a switch of the pattern of expression within the different stages of odontoblast differentiation. Decorin mRNA was expressed earlier in newly differentiating odontoblasts than biglycan. With odontoblast maturation and dentin formation, decorin mRNA expression was diminished and localized to the newly differentiating odontoblasts at the cervical region. Simultaneously, biglycan mRNA took over and extended its expression throughout the new and mature odontoblasts. Both mRNAs were expressed in the dental pulp underlying the respective odontoblasts. At P7.0, both mRNAs were weakly expressed but maintained their spatial expression patterns. Immunostaining showed that biglycan was localized in the dental papillae and pulp. In addition, all four SLRPs showed clear immunostaining in predentin, although the expressions of fibromodulin and lumican mRNAs were not identified in the tooth germs examined. The organ culture data obtained supported the histological findings that biglycan is more predominant than decorin at the apposition stage. These results were used to identify biglycan as the principal molecule among the SLRPs investigated. Our findings indicate that decorin and biglycan show spatial and temporal differential expressions and play their own tissue-specific roles in tooth development.

中文翻译：

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小分子富含亮氨酸的蛋白聚糖在发展中的小鼠磨牙牙胚中的表达，定位和合成。

在假设它们与牙齿形成密切相关的前提下，分析了富含亮氨酸的小蛋白聚糖（SLRP）的基因表达和蛋白质合成，包括得体蛋白，双糖链蛋白聚糖，纤维调节蛋白和发光素。使用ICR小鼠在胚胎天（E）13.5至产后天（P）7.0在不同发育阶段的小鼠第一磨牙牙胚中进行原位杂交，免疫组化和带有[35S]代谢标记的器官培养。在芽和帽阶段，decorin mRNA仅在周围的间充质中表达，而在牙胚中不表达。然后在凝结的间充质和牙胚的牙乳头中表达双糖链蛋白mRNA。在并置阶段（晚期钟形阶段），成牙本质细胞中decorin和biglycan mRNA均表达，导致成牙本质细胞分化不同阶段的表达方式发生变化。Decorin mRNA在新分化的成牙本质细胞中的表达早于biglycan。随着成牙本质细胞的成熟和牙本质的形成，decorin mRNA的表达减少，并定位在子宫颈区域新分化的成牙本质细胞。同时，双糖链蛋白mRNA接管并在整个成熟成牙本质细胞中扩展了其表达。两种mRNA均在相应成牙本质细胞的牙髓中表达。在P7.0，两个mRNA均表达较弱，但仍保持其空间表达模式。免疫染色显示双链蛋白聚糖位于牙乳头和牙髓中。此外，所有四种SLRP均在predentin中显示出清晰的免疫染色，尽管在所检查的牙胚中未鉴定出纤维调节蛋白和卢米肯mRNA的表达。获得的器官培养数据支持组织学发现，在并置阶段，双链蛋白聚糖比decorin更占优势。这些结果被用来确定双链糖蛋白是所研究的SLRP中的主要分子。我们的发现表明，decorin和biglycan可显示时空差异表达，并在牙齿发育中发挥其自身的组织特异性作用。