This is only conceivable because cephalopods have the most complicated brains of any known creature. The procedure, though, is still a mystery. For a long time, researchers have pondered the origin of the large brains of cephalopods. Researchers at Harvard think they may have solved the mystery of how these soft-bodied organisms interpret visual information, which occupies almost two-thirds of their brains. They report that the procedure has a striking resemblance to something they’re already familiar with.
The FAS Center for Systems Biology describes how they used live imaging to observe neuron development in the developing embryo. They followed the cells as they differentiated into other retinal neurons. They found that the behavior of the neural stem cells they were studying was eerily similar to that of neural stem cells in vertebrates during nervous system development. This finding not only suggests that vertebrates and cephalopods, which split off from one another 500 million years ago, use similar mechanisms to make their large brains, but that the process itself, as well as the way the cells act, divide, and are shaped, may essentially lay out the blueprint needed to develop this type of nervous system.
The researchers in the Koenig Lab studied the retina of the Doryteuthis pealeii squid, also known as a longfin squid. The squid can reach a length of approximately a foot, and there are plenty of them in the waters off the northwest coast of Africa. As embryos, they have huge heads and big eyes. The methods employed by the researchers were quite similar to those widely used to examine fruit flies and zebrafish as model organisms. To observe the behavior of individual cells, they developed unique instruments and made use of state-of-the-art microscopes that could acquire high-resolution photos every 10 minutes for hours on end. So that they could map and follow the cells, researchers utilized fluorescent dyes to identify them.
The group used this live-imaging method to study the structure of stem cells known as brain progenitor cells. These cells organize themselves into a structure known as pseudostratified epithelium. Its primary distinguishing feature is the elongation of its cells, which allows for their close proximity to one another. Before and after dividing, the scientists also observed the nucleus of these formations moving up and down. According to them, this motion is crucial for maintaining tissue order and sustaining growth.
All vertebrate species follow this basic blueprint when maturing their brain and eyes. Historically, it was thought to be one of the factors that allowed the huge and sophisticated vertebrate nervous system. This sort of neural epithelium has been found in other species, but the squid tissue studied here was strikingly similar in size, structure, and nucleus movement to vertebrate tissues.
The emergence of specific cell types in the brains of cephalopods is the next topic to be investigated by the group. Koenig is interested in learning whether they are activated at various times, how they choose to become one kind of neuron rather than another, and if this action is conserved throughout species.
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