Squid are one of the smartest ocean dwellers. Along with other ink-squirting leaf horns such as octopuses and squid, octopuses have the largest brains of all invertebrates. They also have an incredibly complex nervous system that can instantly camouflage their bodies and communicate with each other with various signals.
Scientists have wondered about these refined behaviors and have tried to understand why these tentacled creatures are so intelligent. Gene editing can help researchers discover the mysteries of the kephalopod brain. But so far it has been too difficult to do – in part because kephalopod embryos are protected by a hard outer layer that makes manipulating them difficult.
Recently, a group of marine scientists managed to manipulate the first genetically modified squid using the DNA processing tool CRISPR. In addition to being a major milestone in biology, it has potential implications for human health: Because of its large brain, cephalopods are used to study neurodegenerative diseases such as 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, such as specific kephalopod behaviors. ‘I think you will see a big jump in the use of this [gene-edited] organisms by neurobiologists, ”says Joshua Rosenthal, PhD, a senior scientist at the Marine Biology Laboratory in Woods Hole, Massachusetts, and a major architect of the first genetically engineered squid. OneZero.
Rosenthal and his colleagues used CRISPR to cut out a gene responsible for the color of the ink’s skin. As a result, the processed inks were transparent instead of their usual reddish spots. The results were published July 30 in the journal Current biology.
But why bother making a colorless squid? Rosenthal says the pigmentation gene was a logical starting point for experimentation. “When you see the pigmentation go away, it’s easy to see if editing the genes works,” he explains. If you can think of cephalopod DNA, scientists can better investigate what their individual genes do at a very basic level.
The achievements were not easy. Scientists have successfully created gene-modified mice, monkeys, and other research animals to help them study a variety of behaviors and medical conditions. But until now, they have not been able to manipulate the genes of kephalopods.
For one thing, scientists first needed a map of the squid genome to find the exact spot in their DNA that they wanted to edit. The revenue genome was only recently completed, although it has not yet been published in a peer-reviewed journal. Researchers also needed a way to create and process squid embryos in the lab without causing damage.
Co-author Karen Crawford, PhD, a developmental biologist at St. Mary’s College of Maryland, which studies embryos, found a way to mix the eggs of 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 coating of the squid embryos makes it difficult to penetrate them with a needle. When the team tried to inject the embryos, their needles continued to break. Crawford developed a pair of microscissors to cut a small hole in the coating to get a specially made quartz needle inside. Doing so was especially difficult: a hole that is too large can cause the embryo to leak out. But with Crawford’s technique, they successfully inserted CRISPR into the embryos shortly after fertilization without damage.
The researchers used a species called ‘longfin inshore squid’, which migrates to Cape Cod every spring to dry waters. For decades, scientists have been migrating to Woods Hole, on the southwestern part of Cape Cod, to collect and study these animals. Research into them led to groundbreaking discoveries about nerve impulses that won the 1963 Nobel Prize.
But squid with long fins can not live long in a lab because they get too big. In the future, researchers will try to apply their gene-editing technique to smaller types of ink that can be grown more easily in tanks.
They also want to use CRISPR to track the neural activity of the ink. The technique can be used to insert a so-called “reporter” gene, which produces a fluorescent egg white that illuminates when the nervous system is electrically active. “This is an organism with sensory behavior and a lot of nervous cells,” says Rosenthal. “It would be fun to look at the activity of those nerve cells, many of them at the same time, to try to correlate behavior with activity.”
If they could, scientists could study the brain structure involved in the incredible ability of these animals to camouflage. Squid use their exceptional sight and a kind of skin cells called the chromatophores to change their color almost immediately to hide from predators. These specialized cells are connected to the nervous system.
“Cephalopods have a strange, crazy body plan,” Rosenthal says. “They do not look like another organism.” Scientists are also fascinated by the suckers that line the flexible arms of animals. These suckers can sense their surroundings and process all kinds of sensory information – in essence, kephalopods can “think” with their arms.
But because of their advanced intelligence, genetic manipulation of these animals comes with ethical questions. In Canada and Europe, research on kephalopods 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 kephalopods in research.
Writing in the magazine 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 have studied octopuses point to their large, complex, and refined brains as reasons to study them, and are fully aware of the fact that this may be the whole reason we need to pause. “he said.
As researchers begin to change the genetic code of these animals, they will need to consider how far they need to go.
