Chen E, Yuan Z-A, Wright J T, Hong S P, Li Y, Collier P M, Hall B, D'Angelo M, Decker S, Piddington R, Abrams W R, Kulkarni A B, Gibson C W
Department of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, 240 S. 40th St., Philadelphia, PA, USA.
Calcif Tissue Int. 2003 Nov;73(5):487-95. doi: 10.1007/s00223-002-0036-7. Epub 2003 Sep 10.
Amelogenins are the most abundant secreted proteins in developing dental enamel. These evolutionarily-conserved proteins have important roles in enamel mineral formation, as mutations within the amelogenin gene coding region lead to defects in enamel thickness or mineral structure. Because of extensive alternative splicing of the primary RNA transcript and proteolytic processing of the secreted proteins, it has been difficult to assign functions to individual amelogenins. To address the function of one of the amelogenins, we have created a transgenic mouse that expresses bovine leucine-rich amelogenin peptide (LRAP) in the enamel-secreting ameloblast cells of the dental organ. Our strategy was to breed this transgenic mouse with the recently generated amelogenin knockout mouse, which makes none of the amelogenin proteins and has a severe hypoplastic and disorganized enamel phenotype. It was found that LRAP does not rescue the enamel defect in amelogenin null mice, and enamel remains hypoplastic and disorganized in the presence of this small amelogenin. In addition, LRAP overexpression in the transgenic mouse (wildtype background) leads to pitting in the enamel surface, which may result from excess protein production or altered protein processing due to minor differences between the amino acid compositions of murine and bovine LRAP. Since introduction of bovine LRAP into the amelogenin null mouse does not restore normal enamel structure, it is concluded that other amelogenin proteins are essential for normal appearance and function.
釉原蛋白是发育中的牙釉质中分泌量最多的蛋白质。这些在进化上保守的蛋白质在釉质矿化过程中发挥着重要作用，因为釉原蛋白基因编码区域内的突变会导致釉质厚度或矿化结构出现缺陷。由于初级RNA转录本存在广泛的可变剪接以及分泌蛋白的蛋白水解加工，很难确定单个釉原蛋白的功能。为了研究其中一种釉原蛋白的功能，我们构建了一种转基因小鼠，该小鼠在牙器官分泌釉质的成釉细胞中表达富含亮氨酸的牛釉原蛋白肽（LRAP）。我们的策略是将这种转基因小鼠与最近培育出的釉原蛋白基因敲除小鼠进行杂交，后者不产生任何釉原蛋白，具有严重的釉质发育不全和结构紊乱的表型。结果发现，LRAP不能挽救釉原蛋白基因敲除小鼠的釉质缺陷，在存在这种小的釉原蛋白的情况下，釉质仍然发育不全且结构紊乱。此外，转基因小鼠（野生型背景）中LRAP的过表达导致釉质表面出现凹坑，这可能是由于蛋白质产量过高或由于小鼠和牛LRAP氨基酸组成的微小差异导致蛋白质加工改变所致。由于将牛LRAP引入釉原蛋白基因敲除小鼠中并不能恢复正常的釉质结构，因此得出结论，其他釉原蛋白对于正常的外观和功能至关重要。
