Squid are among the smartest inhabitants of the ocean. Along with other paint-moving cephalopods like octopuses and small seas, the squid boasts the largest brain of all invertebrates. They also have an incredibly complex nervous system capable of instantly 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 trampled creatures are so intelligent. Gene editing may be able to help researchers unravel the mysteries of the cephalopod brain. But so far, it has become very difficult ̵1; in part because cephalopod embryos are protected by a hard outer layer that makes them difficult to manipulate.
Recently, a group of marine scientists managed to create the first genetically modified squid using the CRISPR DNA editing tool. In addition to being a major milestone in biology, progress has potential implications for human health: Because of their large brains, 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, as well as cephalopod-specific behaviors. “I think you’re going to see a big leap in using these [gene-edited] organisms by neurobiologists, “says Joshua Rosenthal, a doctor, senior scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts, and a leading architect of the first genetically generated squid. OneZero.
Rosenthal and colleagues used CRISPR to hijack a gene responsible for squid skin staining. As a result, the edited squid was transparent instead of having their usual reddish spots. The results were published July 30 in the journal Current biology.
But why bother creating a colorless squid? Rosenthal says the pigmentation gene was a logical starting point for experiments. “If you see pigmentation go away, it’s easy to see if gene editing works,” he explains. Being able to interact with cephalopod DNA will allow scientists to better study what their individual genes do at a very basic level.
Achieving it was not easy. Scientists have successfully done mice, monkey editing and other research animals to help them study a range of behaviors and medical conditions. But so far, they had not been successful in manipulating cephalopod genes.
For one thing, scientists first needed a maple of the squid genome to find the exact place in its DNA that they wanted to change. The squid genome was recently completed, though it has not yet been published in a peer-reviewed journal. The researchers also needed a way to create squid embryos in the laboratory and modify 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 under the right conditions to form embryos.
Then, the team had to figure out how to inject the CRISPR system into the embryos. Coating 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 microscopy to capture a small hole in the gear to allow a specially made quartz needle to enter. Doing this was particularly tricky: A hole that is too large can cause the embryo to come out. But using Crawford technique, they successfully injected CRISPR into embryos immediately after fertilization without any damage.
The researchers used a species called the long-tailed squid, which migrates to waters outside Cape Cod each spring. For decades, scientists have traveled to Woods Hole, on the southwestern tip of Cape Cod, to collect and study these animals. Research on them led to major discoveries about nerve impulses that won the Nobel Prize in 1963.
But tall long squid can not live long in a lab because they become too large. In the future, researchers will try to use their gene editing technique on smaller squid species that can grow more easily in tanks.
They also want to use CRISPR to track squid nerve activity. The technique can be used to insert the 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 behavior and a lot of nerve cells,” says Rosenthal. “It would be nice to be able to see the activity of those nerve cells, many of them at a time to try to relate the behavior to the activity.”
If they could do that, scientists could study the brain structure involved in the extraordinary camouflage ability of these animals. Squid use their extraordinary eyesight and a type of skin cell called a chromatophore to change their color almost immediately to hide from predators. These specialized cells are connected to the nervous system.
“Cephalopods have a weird and crazy body plan,” says Rosenthal. “They do not look like any other organism.” Scientists are also fascinated by the sucks left by the flexible wings of animals. These suckers can understand their environment and process all kinds of sensory information – essentially allowing cephalopods to “think” with their wings.
But because of their advanced intelligence, the genetic manipulation of these animals comes with ethical questions. In Canada and Europe, research on cephalopods is highly regulated, but in the United States, there is no such protection. For its part, the Marine Biological Laboratory has come up with its own guidelines on the ethical and human use of cephalopods in research.
Journal writing Animal feeling in 2019, scientists Barbara King and Lori Marino argued that scientists should consider treating these animals when using them for research. “Ironically, most researchers who study octopuses point to their large, complex, and sophisticated brains as the reason they want to study them, completely ignoring the fact that this may be the reason it should give us pause, “they said.
As researchers begin to change the genetic code of these animals, they will need to consider how far they should go.