Collaborative Research: Molecular Genetic Studies of Bdelloid Rotifers

该项目的目标是发现和描述遗传和生态因素，这些因素使一群无脊椎动物，蛭形轮虫，在没有有性繁殖的情况下成功进化了数千万年，尽管其他停止有性繁殖的后生动物几乎总是过早灭绝。具体而言，该项目将(1)确定在蛭形种群内转移的DNA片段的长度和年龄分布。虽然蛭形虫几乎肯定不有性生殖，但最近在天然蛭形虫种群中同源DNA转移的证明似乎代表了一种新的混合形式，其遗传和进化意义尚不清楚。(2)在携带选择性标记的DNA存在的情况下，通过筛选脱水和补水后的蛭状体，确定蛭状体异常的脱水/补水循环是否介导基因向蛭状体基因组的水平转移。在这种条件下发生的基因整合将构成一种以前在后生动物中自然发生的未知的遗传转移形式，如果是同源的，则可能解释最近在蛭形种群中显示的等位基因共享和外源基因的异位结合。(3)通过检测几种轮虫物种的转录基因，更全面地表征蛭形虫中发生的大量外源基因（包括细菌、真菌和植物）的水平转移和异位结合，以确定远亲分类群水平转移基因的性质、来源和可能的功能。更广泛的影响：为什么有性生殖存在，为什么需要父母双方而不是一方来生育后代，这些都是具有基本生物学重要性的问题，也是公众普遍感兴趣的问题，并为公众提供了一个很好的生物学教育机会。在美国国家科学基金会的早期支持下，这个项目的结果在美国和国际媒体上得到了广泛的报道，并被纳入大学生物学课程、生物学教科书和关于生物学和进化的流行书籍中。该项目将培养2名博士后、1名博士生和4名本科生。该项目产生的超过30mb的扇形cDNA序列将存入GenBank，并将在一个网站上提供图形界面，用于检查读取质量、组装覆盖范围、ORF鉴定和注释；利用BLAST或利用关键字对蛭形序列进行注释；下载数据、BLAST搜索结果等。

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.