Osborn Jeffrey W
Department of Dentistry, University of Alberta, Edmonton, Alberta, Canada T6G 2N8.
J Theor Biol. 2008 Dec 7;255(3):338-43. doi: 10.1016/j.jtbi.2008.09.008. Epub 2008 Sep 18.
The problem investigated here is control of the development of tooth shape. Cells at the growing soft tissue interface between the ectoderm and mesoderm in a tooth anlage are observed to buckle and fold into a template for the shape of the tooth crown. The final shape is created by enamel secreted onto the folds. The pattern in which the folds develop is generally explained as a response to the pattern in which genes are locally expressed at the interface. This congruence leaves the problem of control unanswered because it does not explain how either pattern is controlled. Obviously, cells are subject to Newton's laws of motion so that mechanical forces and constraints must ultimately cause the movements of cells during tooth morphogenesis. A computer model is used to test the hypothesis that directional resistances to growth of the epithelial part of the interface could account for the shape into which the interface folds. The model starts with a single epithelial cell whose growth is constrained by 4 constant directional resistances (anterior, posterior, medial and lateral). The constraints force the growing epithelium to buckle and fold. By entering into the model different values for these constraints the modeled epithelium is induced to buckle and fold into the different shapes associated with the evolution of a human upper molar from that of a reptilian ancestor. The patterns and sizes of cusps and the sequences in which they develop are all correctly reproduced. The model predicts the changes in the 4 directional constraints necessary to develop and evolve from one tooth shape into another. I conclude more generally expressed genes that control directional resistances to growth, not locally expressed genes, may provide the information for the shape into which a tooth develops.
本文所研究的问题是牙齿形状发育的控制。在牙胚中外胚层和中胚层之间生长的软组织界面处的细胞，被观察到会发生弯曲和折叠，形成牙冠形状的模板。最终形状是由分泌到褶皱上的牙釉质形成的。褶皱发育的模式通常被解释为对界面处基因局部表达模式的一种反应。这种一致性使得控制问题仍未得到解答，因为它没有解释这两种模式是如何被控制的。显然，细胞遵循牛顿运动定律，所以在牙齿形态发生过程中，机械力和约束最终必定导致细胞的运动。使用计算机模型来测试这样一个假设，即界面上皮部分生长的定向阻力可以解释界面折叠成的形状。该模型从单个上皮细胞开始，其生长受到4个恒定的定向阻力（前、后、中、侧）的约束。这些约束迫使生长的上皮细胞弯曲和折叠。通过在模型中输入这些约束的不同值，可诱导模拟的上皮细胞弯曲并折叠成与人类上磨牙从爬行动物祖先演化而来相关的不同形状。牙尖的模式、大小以及它们发育的顺序都被正确地再现。该模型预测了从一种牙齿形状发育和演变成另一种形状所需的4个定向约束条件的变化。我得出的结论是，更普遍表达的控制生长定向阻力的基因，而非局部表达的基因，可能为牙齿发育的形状提供信息。
