Vandervennet E, Wautier K, Verheyen E, Huysseune A
Royal Belgian Institute of Natural Sciences, Vertebrate Department, 1000 Brussels, Belgium.
J Morphol. 2006 Apr;267(4):516-25. doi: 10.1002/jmor.10418.
The Eretmodini are closely related cichlids endemic to Lake Tanganyika with very divergent oral tooth shapes, ranging from spatulate in Eretmodus to conical in Tanganicodus. To study how closely related cichlids can generate such divergent tooth shapes, we investigated how the enamel organ directs the development of spatulate teeth in Eretmodus cf. cyanostictus (lineage A), both in ontogeny and in adults, and of conical teeth in adult Tanganicodus cf. irsacae, using 3D-reconstructions from serially sectioned tooth germs. The spatulate oral tooth shape that characterizes adult E. cf. cyanostictus (lineage A) is preceded early in ontogeny by a conical tooth shape. We propose two possible hypotheses to account for changes in the folding of the enamel organ (in particular its epithelio-mesenchymal boundary) capable of generating such distinct tooth shapes. Different arguments lead us to favor the hypothesis of an asymmetric growth and differentiation of the enamel organ, such that the tip of a conical tooth corresponds to one "corner" of a spatulate tooth. Applying current molecular models of tooth shape variation, this would imply the existence of asymmetric fields of inhibition. Whether such asymmetric growth reflects the reutilization of a simple mechanism operating in ontogeny has to be clarified.
艾氏丽鱼属是坦噶尼喀湖特有的丽鱼科鱼类，它们亲缘关系密切，但口腔牙齿形状差异很大，从艾氏丽鱼的铲状牙到坦噶尼喀丽鲷的圆锥形牙。为了研究亲缘关系密切的丽鱼科鱼类如何产生如此不同的牙齿形状，我们利用连续切片牙胚的三维重建技术，研究了成釉器在艾氏丽鱼（谱系A）的个体发育和成体阶段如何引导铲状牙的发育，以及在成年坦噶尼喀丽鲷（近似伊氏坦噶尼喀丽鲷）中如何引导圆锥形牙的发育。成年艾氏丽鱼（谱系A）特有的铲状口腔牙齿形状在个体发育早期之前是圆锥形牙齿形状。我们提出了两个可能的假说来解释成釉器折叠（特别是其上皮-间充质边界）的变化，这种变化能够产生如此不同的牙齿形状。不同的论据使我们倾向于成釉器不对称生长和分化的假说，即圆锥形牙齿的尖端对应于铲状牙齿的一个“角”。应用当前牙齿形状变异的分子模型，这将意味着存在不对称抑制场。这种不对称生长是否反映了个体发育中一种简单机制的重新利用，还有待阐明。
