How squid and octopus get their big brains

Summary: The neural stem cells of cephalopods function in a similar way to those of vertebrates during the development of the nervous system.

source: Harvard

Cephalopods—which include octopuses, cuttlefish, and their cuttlefish cousins—are capable of some really attractive behaviours. They can quickly process information to transform shape, color, and even texture, and blend it with their surroundings. They can also communicate, show signs of spatial learning, and use tools to solve problems. They are very smart, and can even get bored.

It’s no secret what makes this possible: cephalopods have the most complex brains of any invertebrates on the planet. But what remains a mystery is the process. Basically, scientists have long wondered how do cephalopods get their big brains in the first place?

The Harvard lab that studies the visual system of these soft-bodied creatures — where two-thirds of central processing tissue is concentrated — thinks they are close to discovering it. They say the process sounds surprisingly familiar.

Researchers from the FAS Center for Systems Biology describe how they used a new live imaging technology to watch neurons being created in an embryo in near real time. Then they were able to trace those cells through the development of the nervous system in the retina. What they saw surprised them.

The neural stem cells they tracked were behaving eerily with the way these cells behave in vertebrates as their nervous system evolved.

It is suggested that vertebrates and cephalopods, although diverging from each other 500 million years ago, not only use similar mechanisms to make their large brains but this process and the way cells function, divide and form may fundamentally paint the blueprint required to develop this type of nervous system.

“Our conclusions were surprising because much of what we know about the development of the nervous system in vertebrates has long been thought to be peculiar to this lineage,” said Christine Koenig, a senior fellow at Harvard University and senior author of the study.

“By noting the fact that the process is very similar, what he suggested to us is that these two systems have independently evolved two very large nervous systems that use the same mechanisms in their construction. What this indicates is that those mechanisms – those tools – that animals use during evolution may be important for building large nervous systems.”

Scientists from the Koenig Laboratory focused on the retina of a cuttlefish named Doryteuthis pealeii, more simply known as a type of longfin squid. Squids grow to be nearly a foot long and are abundant in the Northwest Atlantic Ocean. As fetuses they look absolutely gorgeous with a big head and big eyes.

The researchers used techniques similar to those that have spread to study model organisms, such as fruit flies and zebrafish. They created special tools and used advanced microscopes that could take high-resolution images every ten minutes for hours on end to see how individual cells behave. The researchers used fluorescent dyes to mark the cells so they could map and track them.

This live imaging technology allowed the team to monitor stem cells called neural progenitor cells and how they are organized. The cells form a special type of structure called pseudo-stratified epithelium. The main advantage is that the cells are elongated so that they can be densely packed.

The researchers also saw that the nuclei of these structures moved up and down before and after mitosis. This movement is important for keeping tissues organized and for continued growth, they said.

This type of structure is universal in how vertebrate species develop their brains and eyes. Historically, it was considered one of the reasons why the vertebrate nervous system grows so large and complex. Scientists have observed examples of this type of neuroepithelium in other animals, but the squid tissue they looked at in this case was unusually similar to that of vertebrates in its size, organization, and way of moving the nucleus.

The research was led by Francesca R. Naples and Christina M. Daly, research assistants in Koenig’s lab.

Next, the lab plans to look at how different types of cells appear in the brains of cephalopods. Koenig wants to determine if it is expressed at different times, how they decide to become one type of neuron versus another, and whether this action is similar across species.

Konig is excited about the potential discoveries that lie ahead.

“One of the most important points from this kind of work is how important it is to study the diversity of life,” Koenig said. “By studying this diversity, you can really go back to even basic ideas about our development and our biomedical related questions. You can really talk about those questions.”

About this research in Neuroscience News

author: Juan Celesar
source: Harvard
Contact: Juan Célezar – Harvard
picture: The image is in the public domain

original search: Access closed.
“Evolution of the cephalopod retina shows vertebrate-like mechanisms of neurogenesisWritten by Kristen Koenig et al. current biology

Highlights

Squid retinal progenitor cells undergo interkinetic nuclear migration
Progenitor, post-mitotic, and transcriptionally differentiated cells are identified
Notch signaling may regulate both the retinal cell cycle and cell fate in squid

Summary

Coloid cephalopods, including cuttlefish, cuttlefish, and octopus, have large, complex nervous systems and highly sharp, camera-type eyes. These features are only comparable with the features that evolved independently in the vertebrate lineage.

The size of an animal’s nervous system and the diversity of its component cell types are a result of the strict regulation of cellular proliferation and differentiation in development.

Changes in the process of development during development that lead to a diversity of neuron types and an altered nervous system size are not well understood.

Here, we pioneered live imaging techniques and conducted a functional interrogation to show that squid Doryteuthis pealeii It uses mechanisms during retinal neurogenesis that are characteristic of vertebrate processes.

We find that squid retinal progenitor cells undergo nuclear migration until they exit the cell cycle. We determine the corresponding retinal organization of progenitor, post-mitotic, and differentiated cells.

Finally, we find that Notch signaling may regulate the retinal cell cycle and cell fate. Given the convergent evolution of elaborate visual systems in cephalopods and vertebrates, these findings reveal common mechanisms that underlie the growth of highly proliferative neuronal primitives.

This work highlights mechanisms that may alter the measure of genetic variation and contribute to the evolution of complexity and growth in animal nervous systems.