Developmental Evolution of Avian Digit Homology

项目摘要自从发现鸟类与恐龙的亲缘关系以来，关于鸟类翅膀中趾的身份，发育和系统发育证据之间一直存在差异。绝大多数系统发育证据表明，鸟类的三个永久手指是第一、第二和第三趾，而胚胎学证据表明，这些手指是从其他动物的原基发展而来的，在其他动物中，发展成第二、第三和第四趾。威斯康星州大学法伦博士实验室的最新结果表明，有一种基因表达特征可以区分第一和第二手指，这支持了鸟类手指实际上是第一、第二和（通过推理）第三手指的假设。具体而言，Hoxa-13、Hoxd-13和Hoxd-12的表达见于数字1后面的所有数字中，而数字1不表达Hoxd-12。这项拨款资助了发育生物学实验室（威斯康星州大学的Fallon博士）和进化生物学实验室（耶鲁大学的瓦格纳博士）之间的合作，以跟进这一结果。 本研究的目的是通过实验和比较数据验证从基因表达模式到数字身份的推断。目的：1）检测Hoxa-13、Hoxd-13和Hoxd-12基因的表达模式是否与手指形态发育相关。2)确定Hox基因表达模式和数字身份之间的关联，如博士的Vargas和Fallon所描述的，在四足动物的主要群体中以及在数字的自然变化中是否是保守的。为了实现目标1，Fallon博士将研究Hoxd-12在第一趾原基中的错误表达以及Hoxa-13和Hoxd-13的敲除的影响。为了实现目标2，瓦格纳博士将研究Hoxa-13，Hoxd-13和Hoxd-12在鳄鱼，青蛙和蜥蜴胚胎中的表达，包括两种在进化过程中失去第一趾的物种，Hemiergis peronii和Chalcides chaldices（石龙子）。智力优点：虽然鸟类足趾的身份可以被视为一个重要性有限的主题，但主要科学学科之间对一个科学事实的持续分歧引起了人们的关注。像这样悬而未决的高调争议可能会对进化和发育生物学的学科整合产生腐蚀性影响。因此，拟议的项目力求以发展和演变相结合的办法解决这一问题，寻求两者之间的证据趋同。更广泛的影响：这一建议的广泛影响可以从两个方面来衡量：（1）采用高度跨学科的方法来评估进化发育生物学中的复杂问题;（2）提供丰富的研究和教育资源。 这些培训机会包括博士后培训和新的教师暑期培训。

Project SummaryEver since the discovery of the dinosaur affinities of birds, a discrepancy has persisted between the developmental and the phylogenetic evidence regarding the identity of digits in the bird wing. The preponderance of phylogenetic evidence demonstrates that the three permanent fingers of birds are digits one, two and three, while the embryological evidence demonstrates that these fingers develop from the anlagen that, in other animals, develop into digits two, three and four. Recent results from the laboratory of Dr Fallon, University of Wisconsin, shows that there is a gene expression signature which can distinguish between digit one and digit two, and which supports the hypothesis that the fingers of birds are in fact digits one, two and (by inference) three. Specifically the expression of Hoxa-13, Hoxd-13, and Hoxd-12 is seen in all digits posterior of digit one, while digit one does not express Hoxd-12. This grant funds a collaborative effort between a developmental biology lab (Dr Fallon, University of Wisconsin) and an evolutionary biology lab (Dr Wagner, Yale University) to follow up on this result. The goal of this project is to validate the inference from gene expression pattern to digit identity by using both experimental as well as comparative data. Objectives: 1) test whether the expression patterns of Hoxa-13, Hoxd-13, and Hoxd-12 are causally relevant for the development of digit morphology. 2) Determine whether the association between Hox gene expression patterns and digit identity, as described by Dr's Vargas and Fallon, is conserved among major groups of tetrapods and in the face of natural variation in digit number. To meet objective 1 Dr Fallon will study the effect of Hoxd-12 misexpression in the digit one anlage as well as knockdown of Hoxa-13 and Hoxd-13. To meet objective 2, Dr Wagner will study the expression of Hoxa-13, Hoxd-13, and Hoxd-12 in alligator, frog and lizard embryos including two species which have lost digit one during evolution, Hemiergis peronii and Chalcides chaldices (skinks). Intellectual merit: while the identity of bird digits can be seen as a subject of limited importance, the persisting disagreement among major scientific disciplines about a matter of scientific fact raises concern. Unresolved high profile controversies like this can have a corrosive effect on the disciplinary integration of evolutionary and developmental biology. For that reason the proposed project seeks to resolve this issue with a combined developmental and evolutionary approach seeking a convergence of evidence between them. Broader impact: The broad impact of this proposal is measured in two ways: (1) by employing a highly interdisciplinary approach for evaluating a complex problem in evolutionary developmental biology; and (2) by providing a wealth of research and educational resources. These training opportunities include postdoctoral training and new summer traineeships for teachers.