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Squid are among the smartest ocean dwellers. Along with other ink-squirting cephalopods like octopuses and cuttlefish, squid boast the largest brains of all invertebrates. They also have an incredibly complex nervous system capable of instantaneously camouflaging their bodies and communicating with each other using various signals.
Scientists have long marveled at these sophisticated behaviors and have tried to understand why these tentacled creatures are so intelligent. Gene editing may be able to help researchers unravel the mysteries of the cephalopod brain. But until now, it’s been too hard to do - in part because cephalopod embryos are protected by a hard outer layer that makes manipulating them difficult.
Recently, a group of marine scientists managed to engineer the first genetically altered squid using the DNA editing tool CRISPR. In addition to being a big milestone in biology, the advance has potential implications for human health: Because of their big brains, cephalopods are used to study neurodegenerative diseases like Alzheimer’s and Parkinson’s.
The ability to edit the genes of these animals could help scientists study the genes involved in learning and memory as well as specific cephalopod behaviors. “I think you’re going to see a huge jump in the use of these [gene-edited] organisms by neurobiologists,” Joshua Rosenthal, PhD, a senior scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts, and a key architect of the first genetically engineered squid, tells OneZero.
Rosenthal and his colleagues used CRISPR to snip out a gene responsible for the coloring of the squid’s skin. As a result, the edited squid were transparent instead of having their usual reddish spots. The results were published July 30 in the journal Current Biology.
But why bother to create a colorless squid? Rosenthal says the pigmentation gene was a logical starting place for experimentation. “If you see the pigmentation go away, it’s easy to see if the gene editing is working,” he explains. Being able to tinker with cephalopod DNA will allow scientists to better study what their individual genes do at a very basic level.
The accomplishment wasn’t easy. Scientists have successfully made gene-edited mice, monkeys, and other research animals to help them study a range of behaviors and medical conditions. But until now, they hadn’t been successful at manipulating the genes of cephalopods.
For one thing, scientists first needed a map of the squid’s genome to find the precise place in its DNA that they wanted to edit. The squid genome was only recently completed, though it hasn’t been published in a peer-reviewed journal yet. Researchers also needed a way to create squid embryos in the lab and edit them without causing damage.
Co-author Karen Crawford, PhD, a developmental biologist at St. Mary’s College of Maryland who studies animal embryos, figured out a way to mix eggs from a female squid and sperm from a male squid in the appropriate conditions to form embryos.
Then, the team had to figure out how to inject the CRISPR system into the embryos. The squid embryos’ coating makes it difficult to penetrate them with a needle. When the team tried injecting the embryos, their needles kept breaking. Crawford developed a pair of microscissors to snip a tiny hole in the coating to allow a specially-made quartz needle to get inside. Doing so was especially tricky: A hole that’s too big can cause the embryo to ooze out. But using Crawford’s technique, they successfully injected CRISPR into the embryos soon after fertilization without any damage.
The researchers used a species called the longfin inshore squid, which migrates to the waters off Cape Cod every spring in droves. For decades, scientists have trekked to Woods Hole, on the southwest tip of Cape Cod, to collect and study these animals. Research on them led to breakthrough discoveries about nerve impulses that won the Nobel Prize in 1963.
But longfin inshore squid can’t live long in a lab because they get too big. In the future, the researchers will try using their gene-editing technique on smaller species of squid that can be more easily grown in tanks.
They also want to use CRISPR to track the squid’s neural activity. The technique can be used to insert a so-called “reporter” gene, which makes a fluorescent protein that lights up when the nervous system is electrically active. “This is an organism with sophisticated behaviors and a lot of nerve cells,” Rosenthal says. “It would be nice to be able to look at the activity of those nerve cells, lots of them at a time to try to correlate behavior with activity.”
If they can do so, scientists could study the brain structure involved in the incredible camouflage ability of these animals. Squid use their exceptional eyesight and a type of skin cell called the chromatophores to almost instantaneously change their color to hide from predators. These specialized cells are connected to the nervous system.
“Cephalopods have a weird, crazy body plan,” Rosenthal says. “They don’t look like any other organism.” Scientists are also fascinated by the suckers that line the animals’ flexible arms. These suckers can sense their environment and process all sorts of sensory information — essentially allowing cephalopods to “think” with their arms.
But because of their advanced intelligence, genetically manipulating these animals comes with ethical questions. In Canada and Europe, research on cephalopods is highly regulated, but in the United States, there are no such protections. For its part, the Marine Biological Laboratory has come up with its own guidelines on the ethical and humane use of cephalopods in research.
Writing in the journal Animal Sentience in 2019, scientists Barbara King and Lori Marino argued that scientists should consider the treatment of these animals when using them for research. “Ironically, most researchers who conduct studies of octopuses point to their large, complex and sophisticated brains as reasons for wanting to study them, completely overlooking the fact that this might be the very reason that should give us pause,” they said.
As researchers begin to alter the genetic code of these animals, they will need to consider how far they should go.