Department of Developmental Neuroscience, United Centers for Advanced Research and Translational Medicine (ART), Tohoku University Graduate School of Medicine, Sendai, Miyagi, 980-8575, Japan.
Department of Ecological Developmental Adaptability Life Sciences, Tohoku University Graduate School of Life Sciences, Sendai, 980-8578, Japan.
Sci Rep. 2019 Sep 6;9(1):12865. doi: 10.1038/s41598-019-49116-x.
Heterodonty is one of the hallmarks of mammals. It has been suggested that, homeobox genes, differentially expressed in the ectomesenchyme of the jaw primordium along the distal-proximal axis, would determine the tooth classes (homeobox code model) based on mouse studies. Because mouse has highly specialized tooth pattern lacking canine and premolars (dental formula: 1003/1003, for upper and lower jaws, respectively), it is unclear if the suggested model could be applied for mammals with all tooth classes, including human. We thus compared the homeobox code gene expressions in various mammals, such as opossum (5134/4134), ferret (3131/3132), as well as mouse. We found that Msx1 and BarX1 expression domains in the jaw primordium of the opossum and ferret embryos show a large overlap, but such overlap is small in mouse. Detailed analyses of gene expressions and subsequent morphogenesis of tooth germ in the opossum indicated that the Msx1/BarX1 double-positive domain will correspond to the premolar region, and Alx3-negative/Msx1-positive/BarX1-negative domain will correspond to canine. This study therefore provides a significant update of the homeobox code model in the mammalian heterodonty. We also show that the modulation of FGF-mediated Msx1 activation contributes to the variation in the proximal Msx1 expression among species.
杂种牙是哺乳动物的特征之一。有研究表明，在颌原基的外胚间充质中沿远-近轴差异表达的同源盒基因，将根据鼠类研究决定牙齿类群（同源盒编码模型）。由于鼠类具有高度特化的牙齿模式，缺少犬齿和前磨牙（牙齿公式：1003/1003，分别为上下颌），因此不清楚所提出的模型是否适用于具有所有牙齿类群的哺乳动物，包括人类。因此，我们比较了各种哺乳动物，如负鼠（5134/4134）、雪貂（3131/3132）以及鼠类的同源盒编码基因表达。我们发现，负鼠和雪貂胚胎颌原基中 Msx1 和 BarX1 的表达域有很大的重叠，但在鼠类中这种重叠很小。对负鼠牙齿原基中基因表达和随后的牙胚形态发生的详细分析表明，Msx1/BarX1 双阳性域将对应于前磨牙区，而 Alx3 阴性/Msx1 阳性/BarX1 阴性域将对应于犬齿。因此，本研究为哺乳动物杂种牙的同源盒编码模型提供了重要的更新。我们还表明，FGF 介导的 Msx1 激活的调节有助于物种间近端 Msx1 表达的变化。
