Genetically engineered cephalopod offers new model for neurobiological research

Scientists at the Marine Biological Laboratory (MBL) have achieved a significant breakthrough by engineering an albino strain of the hummingbird bobtail squid, Euprymna berryi. This remarkable feat, published in Current Biology, has resulted in the creation of an almost transparent organism, providing researchers with unprecedented optical access to observe the nervous system of a living cephalopod.

What makes this accomplishment even more groundbreaking is that it marks the first instance of breeding a genetically engineered cephalopod through multiple generations. This development underscores the tremendous potential of E. berryi as a model organism for neurobiological and various other types of scientific research.

Dr. Joshua Rosenthal, a senior scientist at MBL, who co-led the study alongside MBL Hibbitt Fellow Dr. Caroline Albertin, emphasized the exceptional nature of cephalopods, stating, “There’s a whole lot of incredibly interesting biology surrounding cephalopods, unlike any other invertebrate. We now have a model cephalopod where we can scrutinize biological function at a much higher resolution than before.”

The nervous system and behavior of coleoid cephalopods, such as squid, octopus, and cuttlefish, exhibit an unparalleled complexity among invertebrates. These creatures possess remarkable cognitive abilities, demonstrating the capacity to learn and remember intricate tasks. Cephalopods can solve mazes, employ tools, and even acquire knowledge through observation. They possess the unique capability to instantaneously camouflage themselves, manipulate their environment with their arms and tentacles, and, as revealed by a recent MBL study, adapt to colder temperatures by extensively modifying their RNA.

However, until now, genetic studies on cephalopods have faced limitations due to the lack of an amenable model organism. While extensive research on fruit flies and mice has unveiled the genetic underpinnings of development, behavior, and evolution in these animals, our understanding of these fascinating cephalopods has remained limited due to the absence of appropriate tools. The new study introduces Euprymna berryi as a viable candidate for a model cephalopod, offering advantages such as ease of multi-generational breeding in a laboratory setting and the ability to undergo genetic modifications.

Co-author Dr. Albertin expressed her excitement about the direct and precise examination of gene function in a model cephalopod, stating, “The ability to directly and precisely test gene function in a model cephalopod is exciting because it makes it possible to study the features that make cephalopods special—and it will be an important tool for understanding many different aspects of their unique biology.”

The hummingbird bobtail squid (Euprymna berryi) is a genetically tractable cephalopd model system. Credit: Tim Briggs/MBL Cephalopod Program

To establish the albino lineage of Euprymna berryi, the research team utilized CRISPR-Cas9 genome editing to disable the genes responsible for two pigmentation enzymes. Dr. Cris Niell from the University of Oregon, Eugene, and Dr. Ivan Soltesz from Stanford University then examined the brain activity of the albino squid by introducing a fluorescent dye into its optic lobe.

This dye emitted a glow upon detecting calcium, which is released by the brain during neuronal firing. By projecting a series of images onto a screen in front of the squid, the optic lobe was stimulated, causing the dye to illuminate. This process was captured using an imaging microscope. When the team attempted the same technique with a wild-type squid, the presence of skin pigmentation hindered their ability to visualize the dye clearly.

According to Dr. Rosenthal, this discovery “enables us to explore gene function and cephalopod brains in ways that were previously inaccessible.” Researchers interested in understanding how signals are transmitted through cephalopod brains can now breed albino squid and conduct similar experiments using calcium-activated dyes. Additionally, if scientists wish to genetically modify these squid to investigate other aspects of their biology, this study demonstrates the feasibility of such experiments.

During the course of their investigation, Dr. Rosenthal, Dr. Albertin, and their team made an intriguing observation about Euprymna berryi’s biology. When they deactivated the first pigmentation gene, known as TDO, they anticipated the production of albino squid, as they had previously achieved with another squid species (Doryteuthis) in a study conducted in 2020. Surprisingly, the offspring of E. berryi still exhibited pigmentation. Subsequently, the team realized that a second enzyme called IDO, previously unknown in cephalopods, was also responsible for pigment generation. The reason E. berryi possesses two enzymes seemingly performing the same function remains a mystery.

Dr. Rosenthal, Dr. Albertin, and their colleagues hope that other scientists will further explore the unique characteristics of E. berryi and utilize them to unravel the enigmas of cephalopod biology.

“We encourage the sharing of these animals within the research community,” expressed Dr. Rosenthal. “Cephalopods harbor vast biological novelties. We hope to see researchers utilizing them to ask thought-provoking questions and make groundbreaking discoveries.”

Source: Marine Biological Laboratory

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