WOODS HOLE, Mass.—A team at the Marine Biological Laboratory (MBL) has accomplished the first gene knockout in a cephalopod using the squid Doryteuthis pealeii. The milestone study, led by MBL Senior Scientist Joshua Rosenthal and MBL Whitman Scientist Karen Crawford, is reported in the July 30 issue of Current Biology.
Cephalopods have the largest brain of all invertebrates, a distributed nervous system capable of instantaneous camouflage and sophisticated behaviors, a unique body plan, and the ability to extensively recode their own genetic information within messenger RNA, as well as other distinctive features. These open many avenues for study and have applications in a wide range of fields, from evolution and development to medicine, robotics, materials science and artificial intelligence.
The ability to knock out a gene to test its function is an important step in developing cephalopods as genetically tractable organisms for biological research — augmenting the handful of species that currently dominate genetic studies, like fruit flies, zebrafish and mice. It is also a necessary step toward having the capacity to knock in genes that facilitate research, such as genes encoding fluorescent proteins that can be imaged to track neural activity or other dynamic processes.
The team used CRISPR-Cas9 genome editing to knock out a pigmentation gene in squid embryos, which eliminated pigmentation in the eye and in skin cells (chromatophores) with high efficiency.
“This is a critical first step toward the ability to knock out — and knock in — genes in cephalopods to address a host of biological questions,” Rosenthal said.
Delivering the CRISPR-Cas system into the one-celled squid embryo, which is surrounded by an exceedingly tough outer layer, was much more challenging. The team needed to develop micro-scissors to clip the egg’s surface, and a beveled quartz needle to deliver the CRISPR-Cas9 reagents through the clip.
“CRISPR-Cas9 worked really well in Doryteuthis; it was surprisingly efficient,” added Rosenthal.
Studies with Doryteuthis pealeii have led to foundational advances in neurobiology, beginning with description of the action potential (nerve impulse) in the 1950s, a discovery for which Alan Hodgkin and Andrew Huxley became Nobel Prize laureates in 1963. For decades D. pealeii has drawn neurobiologists from all over the world to the MBL, which collects the squid from local waters.
Rosenthal and colleagues recently discovered extensive recoding of mRNA in the nervous system of Doryteuthis and other cephalopods. This research is under development for potential biomedical applications like pain management therapy. But D. pealeii isn’t an ideal species to develop as a genetic research organism: it’s large, takes up a lot of tank space, and no one has been able to culture it through multiple generations in a lab.
For these reasons, the MBL Cephalopod Program’s next goal is to transfer the new knockout technology to Euprymna berryi, which is a smaller cephalopod species known as the hummingbird bobtail squid. E. berryi are relatively easy to culture to make genetic strains.