A gene-disruption technique currently creating a buzz among geneticists doesn’t disappoint when it comes to its utility in studying mosquitoes. Scientists have discovered that transcription activator-like effector nuclease proteins (TALENs) can be used to edit genes in Aedes aegypti, a mosquito that spreads the dengue virus and is frequently used in the lab as a model for other mosquitoes. TALENS offer researchers a path toward uncovering the function of currently unknown mosquito genes and identifying genes key to the role of mosquitos in transmitting pathogens.
For many model organisms–fruit flies, for example–researchers have collections of mutants that they can study to determine gene function. Although the Aedes aegypti genome sequence was published in 2007, it has not been easy for researchers to determine the function of the genes uncovered during sequencing, said entomologist Zach Adelman of Virginia Polytechnical Institute, an author of the new work. “When you’re talking about mosquitoes, we don’t have libraries or stock centers of mutants,” he said, “but we have a lot of genes that we want to know what they do.”
Adelman has tried other techniques to alter the mosquito genome but, in the hopes of finding an easier and more efficient method, he turned to TALENs, which facilitate the deletion or replacement of genes or gene segments by introducing specific double-strand breaks in DNA.
“It takes a lot of biochemical wrangling to get the zinc finger nucleases or endonucleases to do what you want,” he said. “Whereas TALENs, because they’re so modular, you just put in a sequence.”
To test whether TALENs would work in Aedes aegypti, Adelman’s team deleted a gene that encodes a protein needed for eye pigmentation. Between 20% and 40% of females produced the mutant alleles, and as many as 75% of the offspring of any given female had the mutant phenotype, a lack of eye pigment (1). These rates are far better than any that the researchers have achieved using other methods, said Adelman.
“When we did it, we didn’t think we were getting the right data because it worked so well,” he said. “This works better than anything I’ve ever used in mosquitoes, it’s just phenomenal. It’s been the only thing I’ve ever tried in my career where it worked on the first try and it worked perfectly.”
Now that they’ve shown the utility of TALENs for genetic manipulation in Aedes aegypti, Adelman and his colleagues want to use this system to delete genes thought to be important for the mosquitoes’ ability to carry dengue virus without getting infected and the insects’ drive to seek out and bite humans. But the technology’s impact will be far-reaching, Adelman said.
“This technology goes so far beyond my own program. If you are interested in learning anything about mosquitoes, then the gold standard is to have a mutant for whatever gene or pathway you’re studying, and this allows that.”
1. Aryan, A., M.A.E. Anderson, K.M. Myles, Z.N. Adelman. 2012 TALEN-based gene disruption in the dengue vector Aedes aegypti. PLoS ONE 8(3): e60082. doi:10.1371/journal.pone.0060082