Collaborative Research: Molecular Genetic Studies of Bdelloid Rotifers

这个项目的目标是发现和描述遗传和生态因素，正是这些因素让一群无脊椎动物--蜈蚣轮虫--成功进化了数千万年而没有有性繁殖，尽管其他停止有性繁殖的后生动物几乎总是提前灭绝。具体地说，该项目将(1)确定蜈蚣种群内转移的DNA片段的长度和年龄分布。尽管蜈蚣几乎可以肯定不参与有性繁殖，但最近在天然蜈蚣种群中同源DNA转移的证明似乎代表了一种新的混合形式，其遗传和进化影响尚不清楚。(2)在带有可选择标记的DNA存在的情况下，通过对脱水和复水后的粘虫进行筛选，确定粘虫的异常脱水/再水化循环是否能够介导基因向粘虫基因组的水平转移。在这种条件下发生的基因整合将构成一种以前未知的在后生动物中自然发生的遗传转移形式，如果是同源的，很可能解释最近证明的蜈蚣种群中的等位基因共享和外来基因的异位结合。(3)通过对几个轮虫物种的转录基因的研究，更全面地描述蜈蚣类中发生的大量的外来(包括细菌、真菌和植物)基因的水平转移和异位整合，以确定从远缘类群水平转移的基因的性质、来源和可能的功能。更广泛的影响：为什么有性生殖存在，为什么应该由双亲而不是单亲生育后代，这些都是基本的生物学重要性问题，也是普遍的公众利益，并为公共生物学教育提供了一个极好的机会。在美国国家科学基金会的早期支持下，这个项目的成果得到了美国和国际媒体的广泛报道，并被纳入大学生物课程、生物教科书和关于生物和进化的畅销书。该项目将培养两名博士后科学家、一名博士生和四名本科生。该项目产生的超过30Mb的Bdelloid基因序列将保存在GenBank中，并将在具有图形界面的网站上获得，用于检查读取质量、组装的覆盖范围、ORF鉴定和注释；用于使用BLAST或关键字的BLAST注释来搜索BLAST序列；以及用于下载数据、BLAST搜索的结果等。

The goal of this project is to discover and characterize the genetic and ecological factors that have allowed a group of invertebrate animals, bdelloid rotifers, to evolve successfully for tens of millions of years without sexual reproduction although other metazoan species that cease reproducing sexually almost invariably suffer early extinction. Specifically, the project will (1) Determine the length and age distribution of DNA segments transferred within bdelloid populations. Although bdelloids almost certainly do not engage in sexual reproduction, the recent demonstration of homologous DNA transfer in natural bdelloid populations appears to represent a novel form of mixis, the genetic and evolutionary implications of which are as yet unknown. (2) Determine whether the unusual desiccation/rehydration cycle of bdelloids can mediate horizontal transfer of genes to bdelloid genomes by screening bdelloids after desiccation and rehydration in the presence of DNA carrying a selectable marker. The occurrence of gene integration under such conditions would constitute a form of genetic transfer previously unknown to occur naturally in metazoans and, if homologous, is likely to account for both the recently demonstrated allele sharing in bdelloid populations and the ectopic incorporation of foreign genes. (3) More fully characterize the massive horizontal transfer and ectopic incorporation of foreign (including bacterial, fungal and plant) genes that has occurred in bdelloids by examining transcribed genes of several rotifer species in order to determine the nature, sources, and possible functions of genes horizontally transferred from distantly related taxa. Broader Impacts: Why sexual reproduction exists, why it should take two parents rather than one to produce offspring, are questions of fundamental biological importance that are also of general public interest and afford an excellent opportunity for public education in biology. Results from this project under earlier NSF support have received wide coverage in the US and international media, and have been incorporated into college biology curricula, biology textbooks, and popular books on biology and evolution. The project will train two postdoctoral scientists, a Ph.D. student, and four undergraduates. The more than 30 Mb of bdelloid cDNA sequence generated by the project will be deposited in GenBank and will be available on a website with a graphical interface for examining read quality, coverage of assemblies, ORF identification, and annotation; for searching bdelloid sequences using BLAST or bdelloid annotation using keywords; and for downloading data, the results of BLAST searches, etc.