Mechanisms of Homoplastic Developmental Evolution in the Nematode Male Tail

线虫雄尾同源性发育进化的机制智力价值为了探索生物体的发育结构在多大程度上限制其进化，拟议的工作利用了同源性提供的多个“进化实验”，即独立物种谱系中相似特征的进化。在没有强有力的发育限制的情况下，同源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，如果相同的机制涉及到每个独立的外观的一个功能，发育限制的指示。设计实验是为了测试在发育层次的特定水平上是否存在同质性：即，形态上的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？从与秀丽隐杆线虫相关的小杆线虫的系统发育研究中发现，雄性尾部的两种结构存在同源性，这是一个研究充分的，遗传上可访问的模型，用于阐明发育途径和参与模式化和形态发生的基因。具体而言，在小杆动物的进化过程中，发生了多个独立的变化（1）化学感受器（称为phasephrase）的前后位置之间，相对于3个机械感受器（称为射线），以及（2）雄性尾尖的尖形leptoderan和圆形peloderan形式之间。这些特征可以作为形态进化的一般类别的模型，如异时性和异序性。为了评估同质性的程度，首先将在单个细胞（细胞谱系、融合、形态发生）的水平上检查所涉及的发育过程，以观察在形态学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，以查看其在控制同源形态特征方面是否保守。如果是，则分析指示基因的表达模式以确定途径的相同部分（即，测试基因的上游或下游）每次改变。（确定确切的因果分子或遗传变化并不仅仅是为了解决同质性发生在什么水平;只需要“读出”途径中的几个点来测试表达在哪里是保守的或在物种之间有何不同。）初步结果表明，phasmid位置的演变涉及开关的极性的不对称分裂的一个单一的母细胞（T），提供了一种新的机制，异位（相对定位的进化变化）。Wnt信号通路是一个很好的参与候选者，因为它控制着C。优雅初步数据还表明，微RNA控制的异时途径在尾尖形态的演变中的潜在作用。虽然许多evo-devo的研究集中在转录调控，男性尾尖进化可能提供一个新的模式，转录后调控的发展演变。这个模型也可能提供一个更深层次的机制理解heterochrony（相对时间的进化变化）如何导致形态变异。无论在这两个特征的进化中是否存在任何特定的机制水平上的同质性，最终（超越目前的建议）确定什么样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的工作提供基础，以了解进化发育机制的许多方面。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，纽约大学杆细胞标本集，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，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。研究结果将发表在知名期刊上。不同的本科生将被招募，并单独指导新的研究。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。

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.