"Gene drive" can be localized
GM mosquitoes will be tested in the fight against malaria
Biologists from Harvard University and the Massachusetts Institute of Technology have developed a way to control the spread of artificial mutations in wild populations of animals and bacteria. Using this method, scientists want to test the effectiveness of the gene drive in the extermination of malaria mosquitoes. A preprint of the article is published on the bioRxiv website (Noble et al., Daisy-chain gene drives for the alteration of local populations).
Gene drive is a method that allows you to quickly distribute a human–modified gene in a wild population of animals or plants. For example, an artificial mutation could reduce the fertility and, consequently, the number of malaria mosquitoes, which would help save many human lives. However, it is not known how the destruction of the population will affect the environment. Scientists call this problem a Catch-22, because its solution contradicts itself: in order to test the gene drive for safety, it is necessary to spread mutations in the natural environment.
Scientists have proposed a way out of the vicious circle. They figured out how to make sure that the gene drive could limit itself, first contributing to the spread of the mutant gene, and after a few generations leading to its disappearance.
The idea of the researchers is to carry out a gene drive using three DNA elements, each of which consists of one or more genes. Element A copies and inserts itself into the homologous chromosome in the presence of element B, and element B copies and inserts itself in the presence of element C. Element C itself spreads in the population through normal inheritance, being transmitted only to half of the offspring.
If scientists release thousands of mosquitoes that carry all three elements, then the pairing of genetically modified insects with wild mosquitoes will lead to the fact that all offspring will carry elements A and B, but only half – element C. As a result, according to the laws of inheritance, A and B will first spread rapidly in the population, however after a certain number of generations, element C will practically disappear, followed by element B and, finally, A.
Diagram from the article in bioRxiv – VM
Biologists are planning to conduct the first gene drive tests on nematodes. According to scientists, the spread of the mutant gene will depend on how many animals will be released into the natural environment. It can be done so that almost all individuals living in a certain territory will be carriers of the mutation, but the genes will not be able to spread in a larger population. If the tests are successful, the question of using the technology in places where there is a clear threat to human health from malaria mosquitoes will seriously arise.
CRISPR technology is used to create a gene drive. If one of the parents of an individual was a carrier of a mutant gene, then he can pass it on to his offspring with a 50 percent probability. This is because the parent has two copies of the gene, only one of which is defective. However, CRISPR is able to copy a mutant fragment and insert it into a healthy gene. Thus, the descendants receive a mutation with a 100 percent probability.
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20.06.2016