Mechanisms of Homoplastic Developmental Evolution in the Nematode Male Tail

线虫雄性尾部同质发育进化机制

• 批准号: 0643047
• 负责人: David Fitch
• 金额: --
• 依托单位: New York University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-01 至 2010-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0643047&HistoricalAwards=false
• 关键词: Mechanisms; Homoplastic; Developmental; Evolution; Nematode

Mechanisms of homoplastic developmental evolution in the nematode male tailIntellectual merit To explore the degree to which the developmental architecture of an organism constrains its evolution, the proposed work exploits the multiple "evolutionary experiments" provided by homoplasy, i.e. the evolution of similar features in independent species lineages. In the absence of strong developmental constraints, chances are that homoplastic changes should not occur in the same gene or even the same genetic pathway. On the other hand, if the same mechanism is involved in each independent appearance of a feature, developmental constraint is indicated. Experiments are designed to test whether or not homoplasy exists at a particular level in the developmental hierarchy: i.e., does morphological homoplasy involve the same developmental process, the same genetic pathway, and/or the same part of the pathway? From the phylogenetic studies of rhabditid nematodes related to Caenorhabditis elegans, homoplasy is found in two kinds of structures in the male tail, a well-studied, genetically accessible model for elucidating developmental pathways and genes involved in patterning and morphogenesis. Specifically, during rhabditid evolution, multiple independent changes have occurred (1) between anterior and posterior positions of the chemoreceptive sensilla called phasmids, relative to 3 mechanosensory sensilla called rays, and (2) between the pointed leptoderan and rounded peloderan forms of male tail tips. These characters serve as models for general classes of morphological evolution, such as heterotopy and heterochrony. To assess the degree of homoplasy, the developmental processes involved will first be examined at the level of individual cells (cell lineages, fusions, morphogenesis) to see if development changes the same way during each homoplastic change in morphology. Secondly, at least one candidate genetic pathway will be tested to see if it is conserved in controlling the homoplastic morphological feature. If it is, then expression patterns of indicator genes will be analyzed to determine if the same part of the pathway (i.e., upstream or downstream of the tested gene) changed each time. (Determining the exact causal molecular or genetic change is not required simply to address at what level homoplasy occurred; only a "read-out" of a couple points in the pathway is needed to test where expression is conserved or where it differs between species.) Preliminary results suggest that the evolution of phasmid position involves switches in the polarity of the asymmetric division of a single blast cell (T), providing a novel mechanism for heterotopy (evolutionary change in relative positioning). The Wnt signaling pathway is a good candidate for being involved, as it controls this polarity in C. elegans. Preliminary data also suggest a potential role for the micro-RNA-controlled heterochronic pathway in the evolution of tail tip morphology. Although many evo-devo studies focus on transcriptional regulation, male tail tip evolution may provide a novel model for posttranscriptional regulation in developmental evolution. This model is also likely to provide a deeper mechanistic understanding into how heterochrony (evolutionary change in relative timing) can result in morphological variation. Regardless of whether or not homoplasy exists at any particular mechanistic level in the evolution of these two features, it will be important eventually (beyond the current proposal) to determine what kinds of genes and molecular changes underlie the evolutionary developmental changes. Thus, whatever is discovered, the proposed studies will provide a foundation for future work to understand many aspects of evolutionary developmental mechanisms.Broader impact A major resource used by other scientists and educators for comparative biology, the NYU Rhabditid Collection, will be maintained in the course of this research without additional cost. More efficient methods for gene knockdown will be developed to empower nematode systems for other studies by other investigators in comparative functional genomics and evolutionary development. New reagents and antibodies will be developed. Results of the work will be published in well-regarded journals. Diverse undergraduates will be recruited and individually mentored in new research. A PhD student and a postdoctoral associate will receive cross-disciplinary training in evolution, development, and molecular genetics.

线虫雄性尾部的同质发育进化机制智力价值为了探索生物体的发育结构限制其进化的程度，该工作利用了同质性提供的多个“进化实验”，即独立物种谱系中相似特征的进化。在没有强大的发育限制的情况下，同质性变化很可能不会发生在同一基因甚至同一遗传途径中。另一方面，如果特征的每个独立外观都涉及相同的机制，则表明发育限制。实验旨在测试发育层次中的特定水平是否存在同质性：即形态同质性是否涉及相同的发育过程、相同的遗传途径和/或途径的相同部分？通过对与秀丽隐杆线虫相关的小杆线虫的系统发育研究，在雄性尾部的两种结构中发现了同质性，这是一种经过充分研究的、遗传上可访问的模型，用于阐明发育途径以及参与模式和形态发生的基因。具体来说，在横纹肌进化过程中，发生了多种独立的变化（1）称为噬菌体的化学感受器的前部和后部位置之间，相对于称为射线的3个机械感觉感器，以及（2）雄性尾尖的尖足类和圆形足类形式之间。这些特征充当形态进化的一般类别的模型，例如异位性和异时性。为了评估同质性的程度，首先在单个细胞的水平上检查所涉及的发育过程（细胞谱系、融合、形态发生），以查看在形态的每个同质性变化期间发育是否以相同的方式变化。其次，将测试至少一个候选遗传途径，看看它在控制同质形态特征方面是否保守。如果是，则将分析指示基因的表达模式，以确定途径的同一部分（即测试基因的上游或下游）是否每次都发生变化。 （确定确切的因果分子或遗传变化并不只是简单地解决同质性发生的水平；只需要“读出”途径中的几个点来测试表达的保守性或物种之间的差异。）初步结果表明，噬粒位置的进化涉及单个母细胞（T）不对称分裂极性的转换，为异位性提供了一种新的机制（进化论） 相对位置的变化）。 Wnt 信号通路是参与其中的一个很好的候选者，因为它控制着秀丽隐杆线虫的这种极性。初步数据还表明，micro-RNA 控制的异时途径在尾尖形态进化中具有潜在作用。尽管许多进化-发育研究侧重于转录调控，但雄性尾尖进化可能为发育进化中的转录后调控提供新的模型。该模型还可能提供对异时性（相对时间的进化变化）如何导致形态变异的更深入的机制理解。无论这两个特征的进化中是否在任何特定的机制水平上存在同质性，最终（超出当前的提议）确定哪些类型的基因和分子变化是进化发育变化的基础将是重要的。因此，无论发现什么，拟议的研究都将为未来了解进化发育机制的许多方面的工作奠定基础。 更广泛的影响 其他科学家和教育工作者用于比较生物学的主要资源纽约大学小杆状病毒收藏将在本研究过程中得到维护，无需额外费用。将开发更有效的基因敲除方法，以使线虫系统能够用于其他研究人员在比较功能基因组学和进化发展方面的其他研究。将开发新的试剂和抗体。该工作的结果将发表在备受推崇的期刊上。新研究将招募不同的本科生并对其进行单独指导。一名博士生和一名博士后将接受进化、发育和分子遗传学方面的跨学科培训。