Collaborative Research: Unraveling the phylogenetic and evolutionary patterns of fragmented mitochondrial genomes in parasitic lice

线粒体对生物体的生存至关重要，因为它们提供细胞功能所需的能量。由于它们的重要性，即使线粒体的微小变化也会对细胞产生剧烈的影响。这包括线粒体中包含遗传信息的分子（染色体）的变化。线粒体中的遗传信息通常包含在单个圆形染色体上。然而，某些种类的虱子（哺乳动物和鸟类的小型寄生昆虫）的线粒体中的染色体被分离成几个更小的圆形片段。在虱子的进化史中，染色体碎片多次出现，但在大多数其他动物中非常罕见且有害。很少有人知道这些碎片化的染色体如何或为什么存在于虱子中。在这个项目中，研究人员将通过比较许多不同种类的虱子的遗传信息来了解线粒体染色体的碎片化。这项研究的结果将提供对细胞如何工作的深入了解，并可以帮助科学家更好地了解人类线粒体疾病。该项目将通过在社区STEM活动中创建展示和演讲，为阿肯色州、印第安纳州和伊利诺伊州的多个推广机会提供支持。该项目还将为从事该项目的博士后研究员、研究生和本科生提供培训，并通过两个分析线粒体基因组数据的讲习班为更广泛的研究界提供培训。研究将集中在三个与虱子线粒体基因组片段化（有丝分裂基因组）相关的假设上：1)无功能、核编码的线粒体基因可能导致有丝分裂基因组片段化；2)有丝分裂基因组片段化允许减少从有丝分裂核不相容中进行的纯化选择；3)选择平衡数量的线粒体基因拷贝可以促进碎片化的增加。为了验证这些假设，研究人员将使用全基因组序列数据来组装来自444种虱子的有丝分裂基因组和相关核基因，这些虱子代表着有丝分裂基因组分裂程度不同的四个不同分支。有了这些数据，研究人员将重建有丝分裂基因组结构的进化史，并比较四个虱子分支的基因组内容。具体来说，研究人员将1)估计一个系统基因组树来重建线粒体断裂的进化模式，2)检查核编码线粒体基因的缺失，3)测试宽松或积极选择的特征，4)量化线粒体基因的相对拷贝数。该项目由系统学和生物多样性科学以及促进竞争研究的既定计划（EPSCoR）共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Mitochondria are critical for the survival of organisms because they provide the energy necessary for cells to function. Because of their importance, even small changes to the mitochondria can have drastic consequences for the cell. This includes changes to the molecules (chromosomes) that contain genetic information in the mitochondria. Genetic information in the mitochondria is usually contained on a single, circular chromosome. However, chromosomes in the mitochondria of some species of lice (small, parasitic insects of mammals and birds) are separated onto several smaller, circular fragments. Fragmented chromosomes arose multiple times throughout the evolutionary history of lice, but are very rare and harmful in most other animals. Very little is known about how or why these fragmented chromosomes exist in lice. In this project, the researchers will seek to understand fragmented mitochondrial chromosomes by comparing genetic information from many different species of lice. The results from this research will provide insight into how cells work and could help scientists to better understand human mitochondrial diseases. The project will support multiple outreach opportunities in Arkansas, Indiana, and Illinois through the creation of displays and presentations at community STEM events. The project will also provide training for a postdoctoral researcher, graduate students, and undergraduate students working on the project, and for the broader research community through two workshops on analyzing mitochondrial genome data. The research will focus on three hypotheses related to fragmented mitochondrial genomes (mitogenomes) in lice: 1) non-functional, nuclear-encoded mitochondrial genes can result in fragmentation of the mitogenome, 2) fragmented mitogenomes allow for a reduction in purifying selection from mito-nuclear incompatibility, and 3) selection for a balanced number of mitochondrial gene copies can promote an increase in fragmentation. To test these hypotheses, the researchers will use whole genome sequence data to assemble mitogenomes and relevant nuclear genes from 444 species of lice that represent four distinct clades that have varying levels of mitogenome fragmentation. With these data, the researchers will then reconstruct the evolutionary history of mitogenome structure and compare genomic content in the four clades of lice. Specifically, the researchers will 1) estimate a phylogenomic trees to reconstruct the evolutionary patterns of mitochondrial fragmentation, 2) examine the absence of nuclear-encoded mitochondrial genes, 3) test for signatures of relaxed or positive selection, and 4) quantify the relative copy number of mitochondrial genes. This project is jointly funded by Systematics and Biodiversity Science and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.