Summary: The neural stem cells of cephalopods act similarly to those of vertebrates during the development of the nervous system.
Cephalopods – which include octopus, squid and their cousins the cuttlefish – are capable of some truly charismatic behaviors. They can quickly process information to transform shape, color and even texture, blending into their surroundings. They can also communicate, show signs of spatial learning, and use tools to solve problems. They are so smart that they can even get bored.
It’s no secret what makes this possible: cephalopods have the most complex brains of any invertebrate on the planet. What remains mysterious, however, is the process. Basically, scientists have long wondered how cephalopods get their big brains in the first place?
A Harvard lab studying the visual system of these soft-bodied creatures – where two-thirds of their central processing tissue is concentrated – thinks they’re on the verge of figuring it out. The process, they say, feels surprisingly familiar.
Researchers from the FAS Center for Systems Biology describe how they used a new live imaging technique to observe the creation of neurons in the embryo in near real time. They were then able to follow these cells through the development of the nervous system in the retina. What they saw surprised them.
The neural stem cells they tracked behaved eerily similar to how these cells behave in vertebrates during the development of their nervous systems.
This suggests that vertebrates and cephalopods, despite diverging from each other 500 million years ago, not only use similar mechanisms to make their large brains, but that this process and the way cells act, divide and shape can essentially lay out the required plan. develop this type of nervous system.
“Our findings were surprising because much of what we know about the development of the nervous system in vertebrates has long been thought to be special to this lineage,” said Kristen Koenig, John Harvard Fellow Emeritus and lead author of the study.
“Observing the fact that the process is very similar, what he suggested to us is that these two very large, independently evolved nervous systems use the same mechanisms to build them. What this suggests is that these mechanisms – these tools – that animals use during development may be important for building large nervous systems.
Koenig lab scientists focused on the retina of a squid called Doryteuthis pealeii, more simply known as a type of longfin squid. The squid reach about a foot in length and are abundant in the northwest Atlantic Ocean. As embryos, they look quite adorable with a big head and big eyes.
The researchers used techniques similar to those made popular to study model organisms, such as fruit flies and zebrafish. They created special tools and used state-of-the-art microscopes capable of taking high-resolution images every ten minutes for hours to observe the behavior of individual cells. The researchers used fluorescent dyes to mark the cells so they could map and track them.
This live imaging technique allowed the team to observe stem cells called neural progenitor cells and their organization. Cells form a special type of structure called pseudostratified epithelium. Its main characteristic is that the cells are elongated so that they can be densely packed.
The researchers also saw the core of these structures move up and down before and after the split. This movement is important for maintaining tissue organization and 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 the vertebrate nervous system could grow so large and complex. Scientists have observed examples of this type of neural epithelium in other animals, but the squid tissue they examined in this case was unusually similar to vertebrate tissue in its size, organization, and the way the core was moving.
The research was led by Francesca R. Napoli and Christina M. Daly, research assistants at Koenig Lab.
Next, the lab plans to examine how different cell types emerge in the brains of cephalopods. Koenig wants to determine if they express themselves at different times, how they decide to become one type of neuron rather than another, and if this action is similar across species.
Koenig is excited about the potential discoveries that lie ahead.
“One of the big lessons from this kind of work is how valuable it is to study the diversity of life,” Koenig said. “By studying this diversity, you can actually come back to fundamental ideas about even our own development and our own relevant biomedical questions. You can really answer these questions.
About this neuroscience research news
Author: Jean Siliezar
Contact: Juan Siliezar – Harvard
Image: Image is in public domain
Original research: Access closed.
“Retinal development of cephalopods shows mechanisms of neurogenesis similar to those of vertebrates” by Kristen Koenig et al. Current biology
The retinal development of cephalopods shows mechanisms of neurogenesis similar to those of vertebrates
- Squid retinal progenitor cells undergo interkinetic nuclear migration
- Progenitor, post-mitotic and differentiated cells are defined by transcription
- Notch signaling can regulate both retinal cell cycle and cell fate in squid
Coleoid cephalopods, including squid, cuttlefish, and octopus, have large, complex nervous systems and high-acuity camera-like eyes. These traits are comparable only to characteristics that have evolved independently in the vertebrate lineage.
The size of animal nervous systems and the diversity of their constituent cell types result from the tight regulation of cell proliferation and differentiation during development.
Changes in the developmental process during evolution that result in a diversity of neural cell types and variable size of the nervous system are not well understood.
Here, we developed live imaging techniques and performed functional interrogations to show that squid Doryteuthis pealeii uses mechanisms during retinal neurogenesis that characterize vertebrate processes.
We find that squid retinal progenitor cells undergo nuclear migration until they exit the cell cycle. We identify the retinal organization corresponding to progenitor, post-mitotic and differentiated cells.
Finally, we find that Notch signaling can regulate both the retinal cell cycle and cell fate. Given the convergent evolution of elaborate visual systems in cephalopods and vertebrates, these results reveal common mechanisms that underlie the growth of highly proliferative primordial neurogens.
This work highlights mechanisms likely to alter ontogenetic allometry and contribute to the evolution of the complexity and growth of animal nervous systems.
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