Mosquitoes are one of humanity’s greatest enemies, spreading to nearly 700 million people annually and estimated to kill more than 1 million people.
Craig Montell, a prominent professor at the University of California, Santa Barbara, is a breakthrough in one method for controlling the population of Aedes aegypti, a vector of dengue, yellow fever, Zika fever and other viruses. Was raised.Studies published in Minutes of the National Academy of SciencesDocuments the first use of CRISPR / Cas9 gene editing to target specific genes associated with male mosquito birth. Researchers have since been able to determine how this mutation can suppress the birth of female mosquitoes.
Montel and his co-authors have been working to improve the practice of vector animal control called the Sterile Infertility Technology (SIT). To control populations, scientists raise many sterile male insects. Then they release these males in numbers that overwhelm their wild opponents. The idea is that females that mate with infertile males before finding a fertile male will become infertile in their own right, thereby reducing the size of the next generation. Repeating this technique several times can dramatically reduce the population. In addition, each generation is smaller than the last generation, so releasing the same number of sterile males will have a stronger effect over time.
SIT has proven to be effective in managing many agricultural pests, including the Mediterranean fruit fly (Mediterranean fruit fly), California’s leading pest. It was also attempted in Aedes aegypti in Africa, but has become an invasive species in many parts of the world due to climate change and global travel.
In the past, scientists used chemicals or radiation to kill male Aedes aegypti. “There are so many genes that affect childbirth that a random rupture of a large number of genes can make a man infertile,” said Montel, a professor of molecular, cellular, and developmental biology at Dagan. .. However, chemicals and radiation have affected animal health and have been less successful in mating with females, compromising the effectiveness of sterile insect technology.
Montel saw the need for a more targeted approach with less collateral damage. He and his colleagues, including co-lead authors Jieyan Chen and Junjie Luo, have undertaken mutations in mosquito genes that cause infertility, especially in men, without affecting insect health. The best candidate they found was b2-tubulin (B2t). Mutations in the associated B2t gene in fruit flies are known to cause male sterility.
Using CRISPR / Cas9, researchers knocked out a male Aedes aegypti B2t. They found that mutant males did not produce sperm, but unlike previous efforts, sterile studs were otherwise perfectly healthy. There has been some debate as to whether sperm (although defective sperm from sterile males) are needed to infertile female mosquitoes, or whether semen transfer alone is sufficient.
In one experiment, researchers introduced 15 mutant males into a group of 15 females for 24 hours. They then exchanged B2t males for 15 wild-type males and left them there. “In essence, all females remained sterile,” Montel said. This confirmed that B2t males can suppress female birth without producing sperm.
The team then set out to determine how timing would work. They exposed females to mutant males for different times. Scientists noticed little difference after 30 minutes, but women’s childbirth declined shortly thereafter. Montel said the females copulated twice on average, even in the first 10 minutes. This showed him that females had to mate with many infertile males before they became infertile.
Combining women and B2t men for 4 hours reduces the birth rate of women to 20% of normal. Eight hours later, the numbers began to level off at about 10%.
Based on the insights from the time trial, the team sought to estimate the SIT under more natural conditions. They added different proportions of B2t and wild-type males simultaneously to a population of 15 females for a week and recorded female births. The ratio of about 5 or 6 sterile males to 1 wild-type male reduced female births by half. The 15: 1 ratio suppressed childbirth to about 20%, where it leveled off.
Currently, Aedes aegypti populations can easily recover from an 80% drop in fertility, Montel said. The success of the SIT stems from the subsequent continuous release of sterile males. Each release is more effective than the last release, as sterile males account for an ever-growing proportion of the population.
Montel plans to continue investigating mosquito mating and fertility behaviors. They are sterile only in the wild, not in the laboratory, as they devise ways to maintain a stock of B2t males. In addition, they characterize male mating behavior to reveal new ways to control mosquito populations.
“Because Aedes aegypti affects the health of many people, I am very interested in studying many aspects of Aedes aegypti,” says Monter, who has done a lot of research with fruit flies in the past. Said. “A pandemic due to mosquito-borne diseases occurs every year.”
“When CRISPER / Cas9 was launched a few years ago, it only offered a new opportunity to do things you couldn’t do before,” he continued. “So it seemed like the right time for us to start working on Aedes aegypti.”
Young male fruit flies make females fight more
Jieyan Chen et al. , “Suppression of female birth of Aedes aegypti by male sterile mutation targeting CRISPR” PNAS (2021). www.pnas.org/cgi/doi/10.1073/pnas.2105075118
Courtesy of the University of California, Santa Barbara
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