Coleoid cephalopods, including squid, cuttlefish, and octopus, have large and complex nervous systems and high-acuity, camera-type eyes. To assimilate in with their surroundings, they may quickly process information to change their shape, color, and even texture. Additionally, they may interact with one another, exhibit signs of spatial learning, and utilize tools to address problems. They are so intelligent that when they grow bored, they even commit trouble.
What remains mysterious is: how cephalopods developed those big brains in the first place. A Harvard lab that studies the visual systems of these soft-bodied creatures believes they’ve come close to figuring it out.
Scientists used a new live-imaging technique to watch neurons created in squid embryos almost in real time. They were able to track those cells through the development of the nervous system in the retina.
They were astonished to discover that these neural stem cells behaved remarkably similarly to those in vertebrates during the nervous system formation. The findings imply that although cephalopods and vertebrates separated 500 million years ago, the processes by which both gained large brains were comparable. Additionally, the cells’ actions, divisions, and shapes may effectively follow a blueprint needed for this particular nervous system.
Kristen Koenig, a John Harvard Distinguished Fellow and senior author of the study, said, “Our conclusions were surprising because a lot of what we know about nervous system development in vertebrates has long been thought to be special to that lineage. By observing the fact that the process is very similar, it suggested that these two independently evolved, very large nervous systems are using the same mechanisms to build them. That suggests that those mechanisms — those tools — the animals use during development may be important for building big nervous systems.”
Scientists focused on the retina of a squid called Doryteuthis pealeii. The northwest Atlantic Ocean is home to a large population of squid, which can grow around a foot long. The embryos’ large heads and eyes make them resemble adorable anime characters.
Scientists frequently used approaches to investigate model species like fruit flies and zebrafish. To observe the behavior of individual cells, they developed specialized instruments. They used state-of-the-art microscopes to capture high-resolution images every ten minutes for hours. To map and track the cells, the researchers marked them using fluorescent dyes.
Thanks to the live-imaging technique, scientists could observe stem cells called neural progenitor cells. They also observed their organization. A pseudostratified epithelium is a unique type of structure created by the cells. The cells are elongated so they can be packed tightly, which is its essential characteristic. Additionally, before and following division, scientists found these formations’ nuclei oscillate up and down. This mobility is crucial for maintaining the tissue’s organization and enabling further growth.
This structure is universally seen in brain and eye development in vertebrate species.
Koenig said, “One of the big takeaways from this type of work is just how valuable it is to study the diversity of life. By studying this diversity, you can return to fundamental ideas about our development and our own biomedically relevant questions. You can speak to those questions.”
- Francesca R. Napoli et al. Cephalopod retinal development shows vertebrate-like mechanisms of neurogenesis. Current Biology. DOI: 10.1016/j.cub.2022.10.027