Biological weapons instead of chemistry
Edit the genome – to restore insect resistance to insecticides
Today, insects, plant pests and disease vectors are fought mainly with the help of chemical means of protection. But the effectiveness of such insecticides decreases over time: insects adapt to these drugs in the same way as bacteria adapt to antibiotics. Therefore, we will either have to continue the "chemical war" by creating new insecticides, or go the other way – genetically engineered.
Nowadays, herbivorous insects destroy up to a quarter of the entire world crop of agricultural crops, and hundreds of thousands of people die every year from diseases carried by insects. For example, in African countries where mosquito-borne malaria is widespread, mosquito nets are treated with insecticides and rooms are sprayed.
Natural insecticides have long been used to control insect pests - substances toxic to insects and some other arthropods contained in many wild plants, but today the vast majority of insecticides are not biological, but chemical in origin. An example is pyrethroids, neurotoxic insect poisons, which are a synthetic analogue of natural pyrethrins contained in Dalmatian chamomile and a number of other plants from the Asteraceae family.
"Classical" insecticides, such as pyrethroids and DDT ("dust"), bind to potential-sensitive membrane proteins VGSC, which form sodium ion channels in the axons (long processes) of neurons. As a result, depolarization of neuronal membranes occurs, which leads insects to death. But over time, mutations in the gene encoding the VGSC protein accumulate in pest populations, which allow them to "escape" from the action of such compounds. As a result, the effectiveness of these insecticides is reduced.
One of the non–standard ways to solve this problem is to try to change the insects themselves using genetic engineering methods, in particular, the CRISPR/Cas9 genome editing system.
Such developments have been underway for several years. So, back in 2015, researchers from the University of California at San Diego (USA) the technology of a chain reaction of genome editing (gene drive), which can be used in natural conditions, was described. In fact, we are talking about how to turn a heterozygous mutation (which is present only in one copy of the gene, on one chromosome) into a homozygous one (in both copies of the gene, on two chromosomes).
As is known, the CRISPR/Cas system contains non-coding RNA, which, with the help of the CAS9 enzyme, attaches to the target DNA site and cuts it. Then this gap is "repaired", and this can be done in different ways. For example, simply connect the ends, as a result of which the gene will become non-working. Or you can embed some functional DNA sequence in the incision site.
In particular, it is possible to create such a genetic engineering design that will not just embed the desired mutation into the genome (which will be heterozygous, since it will affect only one chromosome). At the same time, it can also embed an "instruction" for assembling a CRISPR system that can work with a second, homologous chromosome. The result will be the presence of the necessary functional insertion already in both copies of the gene.
Such an "edited" individual, firstly, is highly likely to transmit the mutation to offspring. Secondly, this technology is necessary to create insects with a complete "shutdown" of a certain gene. This cannot be achieved by changing the gene on only one chromosome: thanks to the second, working copy, the protein product will still be produced, albeit in smaller quantities. In this way, for example, it is possible to increase the number of individuals in mosquitoes that cannot become infected with malarial plasmodium.
Now scientists are trying to use this approach to reduce insect resistance to insecticides. In their experiment, they used a population of fruit flies drosophila, in which 83% of individuals had mutations in the vgsc gene, providing them with resistance to neurotoxins. Using CRISPR-Cas9 technology, they created lines in which this mutant gene was replaced with a normal one. As a result, they managed to transform the fly population in just 10 generations so that the proportion of insecticide-resistant individuals fell to 13%.
The researchers plan to use gene drive technology not only to restore "wild-type" VGSC variants in insect populations, but also to introduce new, artificially created, even more sensitive to insecticides. It is also important to develop such genome editing systems that will remain in the population only for a while, and then disappear from it. And since experiments on mammals have shown relatively low efficiency of attempts to change the genome of the population as a whole, its negative consequences in relation to humans, apparently, should not be feared.
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