New Study Unlocks Some of the Mysteries of Cephalopod Biology

A group at the Marine Biological Laboratory (MBL) has successfully created an albino variant of the hummingbird bobtail squid, known scientifically as Euprymna berryi.

As outlined in Today’s issue of Current Biology, this achievement has resulted in a nearly transparent organism, offering scientists unprecedented optical clarity for examining the nervous system in a live cephalopod.

Moreover, this represents the first instance of breeding a genetically engineered cephalopod across multiple generations, showcasing the tremendous potential of E. berryi as a standard cephalopod for neurobiological and other research types.

“There’s a whole lot of incredibly interesting biology surrounding cephalopods, unlike any other invertebrate,” noted co-lead author MBL Senior Scientist Joshua Rosenthal. “We now have a model cephalopod where we can interrogate biological function at much higher resolution than before.”

The nervous system and behavior of coleoid cephalopods, which include squids, octopuses, and cuttlefish, are much more intricate than most invertebrates. These creatures can master complex tasks, solve mazes, utilize tools, and even learn by observing. They can blend into their surroundings instantaneously, manipulate their environment using their arms and tentacles, and, according to a recent MBL study, adapt to colder climates by significantly editing their RNA.

Nevertheless, cephalopod research has lacked an organism suitable for genetic studies. While extensive research on fruit flies and mice has unveiled the genetic underpinnings of their development, behavior, and evolution, the absence of tools for cephalopod biological investigation has left our understanding of these captivating creatures incomplete. This new research introduces Euprymna berryi as an excellent candidate for a standard cephalopod, given its ease of breeding over generations in a laboratory setting and its amenability to genetic modification.

Albertin, the co-author, stated, “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 research group created the albino strain of E. berryi by turning off the genes for two pigmentation enzymes via CRISPR-Cas9 genome editing. Then, co-researchers Cris Niell from the University of Oregon, Eugene, and Ivan Soltesz from Stanford University studied the brain activity of the albino squid. They introduced a fluorescent dye into its optic lobe, which lights up in response to calcium detection, a substance the brain emits when activated. Images were projected onto a screen for the squid, prompting optic lobe activation, making the dye glow, and being recorded using an imaging microscope. This technique, however, was ineffective with a wild-type squid due to its skin pigmentation obstructing a clear view of the dye.

According to Rosenthal, this breakthrough “allows us to look at gene function and cephalopod brains in ways we couldn’t before.” Scientists keen on deciphering how signals are transmitted through cephalopod brains can now breed albino squid and conduct similar experiments using calcium-responsive dye. Moreover, if a researcher wishes to genetically modify these squid to investigate other aspects of their biology, the team’s research validates that such experimentation is feasible.

During their study, Rosenthal and Albertin’s group uncovered an unexpected aspect of E. berryi’s biology. Upon deactivating the first pigmentation gene, known as TDO, they anticipated producing an albino squid, akin to what they had accomplished with a different squid species (Doryteuthis) in a 2020 study.

However, the resulting E. berryi offspring were still pigmented. They soon discovered the pigment was also being produced by a second enzyme, IDO, a protein not previously identified in cephalopods. The reason why E. berryi has two enzymes with seemingly identical functions remains a mystery.

Rosenthal, Albertin, and their associates hope other researchers will delve deeper into E. berryi’s biology and employ this organism to decode the enigmas of cephalopod biology.

“We want to see these animals shared with the research community,” Rosenthal remarked. “Cephalopods contain treasure troves of biological novelty. We want to see people using them to ask thought-provoking questions and come up with novel findings.”

Image Credit: Tim Briggs/MBL Cephalopod Program