The universal X-shredder: Enabling genetic control by sex ratio distortion in agricultural pests and disease vectors

昆虫把大量的疾病传播给人类、动物和植物。它们还直接以农业植物为食，减少农业产量，使最贫穷的人饿肚子，给农民造成巨大的经济损失。世界气候正在发生变化，这使得昆虫能够入侵新的地区并更快地繁殖。不断增长的人口给世界农业系统带来了越来越大的压力，而与此同时，昆虫对我们最强大的武器--杀虫剂的抗药性也越来越强。因此，昆虫对人类健康和社会造成的全球负担预计将增加。这些挑战迫使我们设想可持续控制昆虫的新方法。昆虫遗传控制是生物控制的一种形式，其中释放转基因昆虫减少或消除野生昆虫种群造成危害的可能性。例如，几十年来，大量释放不育的雄性昆虫一直被用来减少许多害虫的种群规模，其中一种遗传控制策略是使种群的性别比例强烈偏向雄性，这样，由于缺乏雌性，种群规模就会减少或完全消失。正常情况下，男性的精子中有一半携带Y染色体并继续制造男性，而另一半携带X染色体并继续制造女性。有一种基因使精子的产生偏向于携带Y染色体的精子，这种基因被称为性别比例扭曲因子。我们第一次产生了这样一种扭曲基因，它通过在许多地方切割X染色体的DNA来破坏X染色体，并成功地在疟疾蚊子中进行了测试。蚊子的生物学特性让我们走了一条捷径，因为可以剪切蚊子X染色体DNA的“分子剪刀”已经存在，而且只需稍加修改就可以使用。在这个项目中，我们想探索是否也可以为许多其他昆虫或媒介物种创造类似的扭曲基因，并摧毁它们各自的X染色体。首先，我们将开发一种生物信息学算法，该算法能够使用雄性和雌性昆虫的DNA序列来识别X染色体可以被切割的位置。然后，我们将使用新的CRISPR“分子切割”技术在精子制造时切割X染色体，并研究对后代的影响。如果这种方法有效，并且只有携带Y染色体的精子存活下来，我们将发现这些昆虫现在大多数都能产生雄性后代。我们将首先在果蝇中测试这种方法，因为果蝇是一种遗传发电站，可以快速有效地完成许多遗传实验。如果成功，我们将在一种经过充分研究的害虫物种中测试这项技术，例如地中海实蝇，它能够破坏许多水果作物。我们将证明，携带扭曲基因的雄蝇与正常蝇群放在一个笼子里，会减少甚至消灭正常蝇群。如果有效，我们的控制策略将来可以应用于保护粮食作物免受虫害或人类和动物免受虫媒疾病的侵害。

Insects transmit a great number of diseases to humans, animals and plants. They also directly feed on agricultural plants, reducing agricultural production and causing empty stomachs for the poorest and huge economic losses for farmers. The world's climate is changing allowing insects to invade new regions and reproduce faster. A growing human population puts a rising strain on the worlds agricultural systems while at the same time insects are becoming increasingly resistant to our most powerful weapon - insecticides. The global burden insects pose on human health and society is therefore expected to increase. These challenges are forcing us to envision novel ways in which we can sustainably control insects.Genetic control of insects is a form of biological control where the release of modified insects reduces or eliminates the potential of wild insect populations to do harm. For example the mass-release of sterilized males has been used to reduce the population size of many insect pests for many decades.One such genetic control strategy is to strongly bias the sex ratio of a population towards males so that the population, due to a lack of females, decreases in size or is eliminated altogether. Normally half of a male's sperm carry the Y-chromosome and go on to make males whereas the other half carries the X chromosome and go on to make females. A gene that biases the production of sperm towards those that carry the Y-chromosome is refereed to as a sex ratio distorter. We have, for the first time, generated such a distorter gene which destroys the X-chromosome by cutting its DNA in many places and successfully tested it in the malaria mosquito. The biology of the mosquito allowed us take a shortcut, as "molecular scissors" that could cut the DNA of the mosquito's X-chromosome were already available and could be used with little modification.In this project we want to explore whether similar distorter genes can also be created for many other insect pest or vector species and to destroy their respective X-chromosomes. First we will develop a bioinformatic algorithm that is able to identify, using DNA sequences from male and female insects, positions where the X-chromosome can be cut. We will then use the novel CRISPR "molecular scissor" technology to cut the X-chromosome when sperm are made and study the effect on the progeny. If it works and only sperm carrying the Y survive we will find that these insects now produce mostly male offspring.We will first test this approach in the fruit fly Drosophila, as the fly is a genetic powerhouse allowing many genetic experiments to be concluded quickly and efficiently. If successful we will then test this technology in one well studied insect pest species for example Ceratitis capitata, the Mediterranean fruit fly capable of damaging many fruit crops. We will show that male flies carrying the distorter gene when placed in a cage with a population of normal flies will reduce that population or even eliminate it.If it works our control strategy can in the future be applied to protect food crops from insect pests or humans and animals from insect-borne diseases.