Mozzies thrive with a gene missing

This may seem hard to believe given their tenacity and constant presence, but mosquitoes lack a gene that is critical for survival in other insects.

The exoskeletons of a normal mosquito larva (left) and one with the gooseberry gene edited out. Credit: Alys Jarvela / University of Maryland

Entomologists from the University of Maryland, US, say it’s the one responsible for properly arranging an insect’s segmented body. In mozzies, a related gene has evolved to do the job.

It is the first time, they say, that scientists have identified a gene that naturally evolved to perform the same critical function as a related gene long after the two genes diverged down different evolutionary paths.

And it emphasises the need for caution in genetic studies that use model animals to make conclusions across different species.

“We learn a lot in biology by studying a process in a model organism and assuming that it works essentially the same way, using the same genes, in other organisms,” says Alys Jarvela, lead author of a paper in the journal Communications Biology.

“That is still an incredibly useful approach, but now we know that there is also a possibility for gene substitutions to be made in nature.”

Jarvela made the initial discovery by accident while studying crickets and cross-checking the gene sequences with those of other insects. She was specifically interested in a gene called paired, which helps guide the pattern of repeated parts in segmented animals.

Laboratory studies have shown that when paired is knocked out or silenced in fruit flies, every other segment of the insect’s body fails to develop, and it doesn’t survive. But it was missing in the mosquitoes she looked at – and in every species represented on the publicly available databases of mosquito genomes she later turned to.

The game was afoot. Her team searched the genomes of fly species closely related to mosquitos and found they all contained the paired gene. This indicated that the loss of paired is a recent evolutionary event that took place only in mosquitos, and that some other gene must be doing its job.

Previous work suggested the ring-in might be a gene called gooseberry, and a little CRISPR editing showed that was the case. Mosquito embryos without gooseberry resembled fruit fly embryos without paired.

“This work shows that even when different species share a trait or feature, the genetic mechanisms underlying this shared trait may be different,” says senior author Leslie Pick.

The next steps will be to search for additional examples of variation in gene regulatory networks in insects and try to determine how genetic rewiring occurs in nature.

And there may be an upside in relation to that mosquito tenacity and constant presence: in fruit flies, paired also influences male fertility.

“That means different genes probably regulate male fertility in mosquitos, and they might be unique to the mosquito, which could potentially provide a powerful avenue for controlling mosquitoes without harming other insects such as butterflies and bees,” Jarvela says.

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