Kangas Aapo T, Evans Alistair R, Thesleff Irma, Jernvall Jukka
Developmental Biology Program, Institute of Biotechnology, PO Box 56, FIN-00014, University of Helsinki, Helsinki, Finland.
Nature. 2004 Nov 11;432(7014):211-4. doi: 10.1038/nature02927.
Studies of mammalian evolution frequently use data derived from the dentition. Dental characters are particularly central for inferring phylogenetic relationships of fossil taxa, of which teeth are often the only recovered part. The use of different aspects of dental morphology as phylogenetic signals implies the independence of dental characters from each other. Here we report, however, that, at least developmentally, most dental characters may be nonindependent. We investigated how three different levels of the cell signalling protein ectodysplasin (Eda) changed dental characters in mouse. We found that with increasing expression levels of this one gene, the number of cusps increases, cusp shapes and positions change, longitudinal crests form, and number of teeth increases. The consistent modification of characters related to lateral placement of cusps can be traced to a small difference in the formation of an early signalling centre at the onset of tooth crown formation. Our results suggest that most aspects of tooth shape have the developmental potential for correlated changes during evolution which may, if not taken into account, obscure phylogenetic history.
对哺乳动物进化的研究经常使用来自齿系的数据。牙齿特征对于推断化石类群的系统发育关系尤为关键，因为牙齿往往是唯一能找到的化石部分。将牙齿形态的不同方面用作系统发育信号意味着牙齿特征彼此独立。然而，我们在此报告，至少在发育过程中，大多数牙齿特征可能并非相互独立。我们研究了细胞信号蛋白外胚层发育不良蛋白（Eda）的三种不同水平如何改变小鼠的牙齿特征。我们发现，随着这一个基因表达水平的提高，牙尖数量增加、牙尖形状和位置改变、纵向嵴形成且牙齿数量增加。与牙尖侧向位置相关特征的一致变化可追溯到牙冠形成开始时一个早期信号中心形成的微小差异。我们的结果表明，牙齿形状的大多数方面在进化过程中具有相关变化的发育潜力，如果不加以考虑，可能会模糊系统发育历史。
