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CRISPR gene processing generates a wave of exotic model organisms



  Hawaiian Bobtail Squid

The Hawaiian Bobtail Squid (Euprymna scolopes) changes the camouflage patterns of its skin based on what it sees. Credit: Eric Roettinger / Kahi Kai Images Ever since he was seventeen, Joseph Parker wanted to know what makes Rove beetles tick. The entomologist has collected and observed insects for decades, some of which live among ants and feed on their larvae. But without tools to study the genetic and brain mechanisms of beetle behavior, Parker focused his PhD thesis on Drosophila fruit flies ̵

1; an established model organism.

Now, more than a decade later, the rise of the CRISPR gene editing technique has brought Parker's childhood dream within reach. He uses CRISPR to study the symbiosis of red beetles ( Staphylinidae ) in his laboratory at the California Institute of Technology in Pasadena. By shutting down genes in beetles that live with ants and in those that do not, Parker hopes to find out how the DNA of insects has changed when their lifestyle has changed. "We design a model system from scratch," he says.

Biologists have adopted CRISPR's ability to rapidly and cost-effectively modify the genomes of popular model organisms such as mice, fruit flies and monkeys. Now they are trying out more exotic species, many of which have never been reared in a laboratory or whose genomes have been analyzed. "We are finally ready to expand what we call a model organism," says Tessa Montague, a molecular biologist at Columbia University in New York City.

Montague works on the Hawaiian Bobtail Squid ( Euprymna scolopes )) and the dwarf squid ( Sepia bandensis ), species whose unusual camouflage acts as brain activity to the outside. The cephalopods project patterns onto their skin to match what they see around them. However, it has been difficult to study how her brain processes stimuli. Researchers would normally do this by inserting electrodes or other sensors into the skull – but squid and squid are boneless.

Montague and her colleagues successfully injected CRISPR components into squid and squid embryos for the first time last year. Now they are trying to genetically modify the cephalopod neurons so that they light up when lit.

Technical Knockout

Other researchers use CRISPR to study the different social behaviors of species. Daniel Kronauer, a biologist at Rockefeller University in New York City, has created Raider ants ( Ooceraea biroi ) that pheromones can not smell. In experiments, the genetically modified ants could not maintain the complex hierarchy of a normal Raider ant colony 1 . Scientists are now using CRISPR to manipulate genes thought to affect the behavior of Raider ants.

Then there are species that threaten the health of humans or the environment – such as the pea aphid ( Acyrthosphion pisum ), an insect that exists worldwide attacks legumes. To process the genome of the aphid with CRISPR, a team led by Shuji Shigenobu, an evolutionary geneticist at the National Institute of Basic Biology in Okazaki, Japan, had to manipulate the complex life cycle of the insect. Summer-born female aphids multiply asexually by cloning themselves, while eggs born in the fall lay eggs.

Shigenobu's team set up an incubator that simulated the cool temperatures and short fall days so the aphids could lay eggs that the scientists could inject with CRISPR components.

After four years, the team managed to edit a pigment gene as a proof of concept, Shigenobu announced last month during a conference at the Howard Hughes Medical Institute's Janelia Research campus in Ashburn, Virginia. He hopes that by modifying other parts of the leaf genome, researchers can learn more about how insects interact with plants. This information could lead to better pesticides.

Inching forward

The development of animal models requires immense time and money, and until recently, there was little support for such work. In 2016, the US National Science Foundation launched a $ 24 million program to create model organisms – uncovering the genetic and molecular mechanisms behind complex features and behaviors.

The program supports research to develop tools to study the genomes of species, study life cycles of organisms, and develop protocols to grow these species in the laboratory. This support pays off: In March researchers from the University of Georgia in Athens 2 said that they had used CRISPR to create the first genetically modified reptile, the brown Anol ( Anolis sagrei ).

Despite these promising early results, the thrust of using CRISPR to create model organisms has shown how little is known about the genomes of many species, lifecycles, and habits. Researchers face practical challenges such as determining how CRISPR components are injected into embryos, and delicate, brittle species are bred to grow in the lab.

"The reason why classic model systems were chosen was essentially pests. Nothing can stop them from growing, "says Montague. "But if we face the challenge of working on new organisms because they have amazing properties, under no circumstances will they grow under [just]."

This forces the scientists to balance the effort required to study a particular trait against the potential rewards. To change a genome requires a deep understanding of the behavior and life cycle of a species – a high order when it is studied by only a handful of people worldwide. "People do not choose these model systems easily," says David Stern, a biologist with Janelia.

Stern knows this first-hand: He and his colleagues produced only one species of fruit fly after discovering that the insects needed a fragrance. Laying eggs – the smell of a particular chemical produced by plants.

Researchers' interest in the development of atypical animal models, however, continues to grow. Montague and her colleagues have developed a tool called CHOPCHOP that allows them to design a CRISPR system to manipulate specific genes in any DNA snippet. So far, scientists have sent their gene sequences from more than 200 different species, including plants, fungi, viruses and farm animals.

"I had this weekly reminder that these molecular tools work in just about every organism on Earth," says Montague. "It's an exciting time to work on every model organism – especially those new and strange creatures."

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