Development Genetics of Tooth Number Variation in Sticklebacks

项目摘要 该项目的长期目标是确定调控牙齿形成和替换的遗传回路。 由于全球65岁以上的人中有30%没有天然牙齿，了解牙齿是如何 再生是生物学的一个主要目标。此外，牙齿就像大多数器官一样，是通过重复的相互作用形成的 上皮细胞和间质细胞之间的信号传递。因此，了解牙齿形成的遗传基础和 替换对于理解器官发生和理解如何发生都很重要。 牙齿可以在体外再生，最终在体内再生。牙齿与其他脊椎动物的皮肤同源 包括哺乳动物的毛发在内的附属物，以及共同的基因都控制着牙齿和头发的形成。虽然 对人类、小鼠和其他脊椎动物的遗传学研究已经确定了与牙齿有关的信号通路 形成，人们对基因如何调控牙齿替换知之甚少。相比之下，基因如何调控 对哺乳动物毛发再生的了解要多得多。一个节俭的假设是牙齿和头发 用相似的遗传线路再生。鱼类保留了祖先有颌骨的脊椎动物恒牙的状态 在成年后的整个生活中都是替补。鱼也大量地在外部使它们的后代受精，为 发育生物学和遗传分析的强大系统。三刺鱼(Gastersteus Aculeatus)为研究牙齿形成和替换的遗传学基础提供了一个新的强大的系统。 相对于低齿海洋祖先，衍生的淡水种群进化出了可遗传的主要增长 牙齿数量和牙齿替换率。不同的表格可以在实验室中交叉，从而实现详细和 无偏见的正向遗传分析，以定位控制牙齿数量变化的因素。遗传和 基因组实验已将一个控制牙齿数量的基因组区域定位于顺式调节内含子 骨形态发生蛋白6(Bmp6)基因的牙齿增强子在一个高牙齿人群中的表达。相对于 海洋增强剂，淡水增强剂表现出牙齿上皮细胞表达的扩大和减少 牙齿间充质细胞的表达，表明这些增强子活性的空间变化是进化增加的原因 在牙数上。此外，在小鼠中，BMP信号负向调节毛发再生，而在鱼类中，BMP信号负向调节毛发再生 信号负向调节牙齿替换。总之，这些数据支持共享的假说 调节牙齿和毛发再生的基因回路。为了验证这一假设，有三个具体目标 建议。首先，转基因和基因组编辑实验将确定淡水中的哪些突变 BMP6增强子影响表达差异和牙数。第二，基因组编辑实验将 确定Wnt配体在牙齿形成和替换过程中的功能。三、活体染料脉冲追逐 实验将测试牙齿替换是否在牙场内协调。这些目标加在一起将 揭示调控牙齿形成和发育的遗传回路的基础知识 更新换代，并为牙齿再生类似于哺乳动物头发的假说提供了进一步的测试。

Project Summary The long-term goal of this project is to identify the genetic circuitry regulating tooth formation and replacement. As 30 percent of people worldwide over the age of 65 have no natural teeth, understanding how teeth regenerate is a major goal in biology. Furthermore, teeth, like most organs, form through repeated reciprocal signaling between epithelia and mesenchyme. Thus, understanding the genetic basis of tooth formation and replacement is important both for understanding organogenesis in general, as well as for understanding how teeth can be regenerated in vitro and ultimately in vivo. Teeth are homologous to other vertebrate skin appendages including mammalian hair, and shared genes regulate both tooth and hair formation. Although genetic studies in humans, mice and other vertebrates have identified signaling pathways involved in tooth formation, less is known about how genes regulate tooth replacement. In contrast, how genes regulate mammalian hair regeneration is much more understood. One parsimonious hypothesis is that teeth and hair regenerate using similar genetic circuits. Fish retain the ancestral jawed vertebrate condition of constant tooth replacement throughout adult life. Fish also fertilize their offspring externally in large numbers, providing powerful systems for developmental biology and genetic analyses. Threespine stickleback fish (Gasterosteus aculeatus) offer a new and powerful system to learn the genetic basis of tooth formation and replacement. Relative to low-toothed marine ancestors, derived freshwater populations evolve major heritable increases in tooth number and tooth replacement rates. The different forms can be crossed in the lab, enabling detailed and unbiased forward genetic analyses to map factors controlling the changes in tooth number. Genetic and genomic experiments have mapped one genomic region controlling tooth number to a cis-regulatory intronic tooth enhancer of the Bone Morphogenetic Protein 6 (Bmp6) gene in one high-toothed population. Relative to the marine enhancer, the freshwater enhancer displays expanded tooth epithelial expression, and reduced tooth mesenchymal expression, suggesting these spatial shifts in enhancer activity underlie evolved increases in tooth number. Furthermore, in mice, BMP signaling negatively regulates hair regeneration, and in fish BMP signaling negatively regulates tooth replacement. Together these data support the hypothesis of shared genetic circuitry regulating tooth and hair regeneration. To test this hypothesis, three specific aims are proposed. First, transgenic and genome editing experiments will determine which mutations in the freshwater Bmp6 enhancer affect expression differences and tooth number. Second, genome editing experiments will determine Wnt ligand function during tooth formation and replacement. Third, vital dye pulse-chase experiments will test whether tooth replacement is coordinated within a tooth field. Together these aims will reveal fundamental knowledge of the developmental genetic circuitry regulating tooth formation and replacement, and provide further tests of the hypothesis that teeth regenerate similar to mammalian hair.