Lu Xuanyu, Ito Yoshihiro, Kulkarni Ashok, Gibson Carolyn, Luan Xianghong, Diekwisch Thomas G H
Brodie Laboratory for Craniofacial Genetics, University of Illinois at Chicago, Chicago, IL, USA.
Eur J Oral Sci. 2011 Dec;119 Suppl 1(Suppl 1):254-60. doi: 10.1111/j.1600-0722.2011.00905.x.
Molecular evolution studies suggest that amelogenin (AMELX), the principal component of the mammalian enamel matrix, emerged considerably later than ameloblastin (AMBN), and enamelin. Here, we created a transgenic mouse model to ask the question how a conceivable basal enamel lacking AMELX and enriched in the more basal AMBN might compare with recent mouse enamel. To answer this question we overexpressed AMBN using a keratin 14 (K14) promoter and removed AMELX from the genetic background by crossbreeding with amelx(-/-) mice. Enamel coverings of amelx(-/-) mice and of the squamate Iguana iguana were used for comparison. Scanning electron microscopic analysis documented that AMBN transgenic (TG) × amelx(-/-) mouse molars were covered by a 5 μm thin 'enameloid' layer resembling the thin enamel of the Iguana squamate. Transmission electron microscopy revealed that the enamel of developing AMBN TG × amelx(-/-) mouse molars contained short (approximately 70 nm) and randomly oriented crystals, while WT controls, AMBN overexpressors, and AMELX(-/-) mice all featured elongated and parallel oriented crystals measuring between 300 and 600 nm in average length. Together, these studies illustrate that AMBN promotes the growth of a crystalline enamel layer with short and randomly oriented crystals, but lacks the ability to facilitate the formation of long and parallel oriented apatite crystals.
分子进化研究表明，牙釉蛋白（AMELX）作为哺乳动物牙釉质基质的主要成分，其出现时间比成釉蛋白（AMBN）和釉蛋白要晚得多。在此，我们创建了一个转基因小鼠模型，以探讨缺乏AMELX且富含更基础的AMBN的假想基础牙釉质与近期小鼠牙釉质相比会是怎样的。为回答这个问题，我们使用角蛋白14（K14）启动子过表达AMBN，并通过与amelx（-/-）小鼠杂交从遗传背景中去除AMELX。将amelx（-/-）小鼠和蜥蜴鬣蜥的牙釉质覆盖物用于比较。扫描电子显微镜分析表明，AMBN转基因（TG）×amelx（-/-）小鼠磨牙被一层5μm厚的“类牙釉质”层覆盖，类似于鬣蜥的薄牙釉质。透射电子显微镜显示，发育中的AMBN TG×amelx（-/-）小鼠磨牙的牙釉质含有短（约70nm）且随机取向的晶体，而野生型对照、AMBN过表达小鼠和AMELX（-/-）小鼠的牙釉质均具有平均长度在300至600nm之间的细长且平行取向的晶体。总之，这些研究表明，AMBN促进了具有短且随机取向晶体的结晶牙釉质层的生长，但缺乏促进形成长且平行取向的磷灰石晶体的能力。
