Sea urchins may seem simple, but recent research reveals they have a surprising complexity. A new study has mapped the cells of young sea urchins, specifically Paracentrotus lividus, showing that their bodies act like a distributed brain instead of having a centralized control center.
Led by Periklis Paganos from the Stazione Zoologica Anton Dohrn, this research uncovered that these juvenile urchins have dense networks of neurons across their bodies. Traditionally, scientists thought of their nervous systems as a simple nerve net. This study challenges that idea.
Using a technique called single-nucleus transcriptomics, researchers analyzed the genes in the cells of two-week-old juveniles. They found 25,000 nuclei divided into 48 molecular clusters, which grouped into eight major families of tissues and organs, including muscles and immune cells. Surprisingly, around two-thirds of these clusters were neurons.
Sea urchins start life as swimming larvae but transform during metamorphosis into bottom-dwelling juveniles. This process involves reorganizing into bodies with a five-part symmetry. Previous studies focused on how genes switched on and off to guide this transformation, but now we see that the same set of genes is reused to create two different body types.
The new atlas identifies 29 types of neurons, each using various neurotransmitters like serotonin and dopamine. This showcases the diversity of their nervous systems, suggesting more complex interactions than previously thought. “This fundamentally changes how we think about the evolution of complex nervous systems,” noted Dr. Jack Ullrich-Lüter from the Natural History Museum in Berlin.
Interestingly, even without eyes, sea urchins respond to light using specialized cells called photoreceptors. Their bodies can detect light from many angles, helping them adapt their movements. Earlier findings showed they have at least seven types of light-sensitive proteins. This study expands on that, revealing 15 different types of photoreceptor neurons, including those sensitive to blue light.
Sea urchins belong to a group known as deuterostomes, which is significant for understanding evolutionary traits shared with vertebrates. The finding that their bodies are neuron-rich reshapes our views on how nervous systems develop across species. As more similar studies emerge in other echinoderms, we can explore if this arrangement is a common strategy or unique to sea urchins.
This groundbreaking research was published in the journal Science Advances.
