Researchers at University of Tsukuba have identified a brain-like cluster of neurons in sea urchin larvae, traditionally considered lacking a brain, that regulates light-responsive behavior. The work is published in the journal Nature Communications.
A cluster of non-visual, light-sensitive neurons was discovered in the anterior apical neuroectoderm of sea urchin larvae. These neurons respond to light stimuli without forming visual images, suggesting the presence of a central regulatory network in echinoderms analogous to the vertebrate brain.
The neuronal cluster expresses non-visual opsin (Opn5L), a light-sensitive protein, as well as key regulatory genes, such as rx, otx, six3, and lhx6, which are involved in vertebrate brain development.
Integrative analysis revealed that functional disruption of Opn5L impairs light-dependent swimming behavior. The molecular profile of these neurons partially overlaps with that of vertebrate brain regions, suggesting the conservation of ancestral brain-like functions in sea urchin larvae.
Comprehensive cross-phylogenetic comparisons of the developmental processes involving non-visual opsin-expressing neurons and their surrounding regions are anticipated to yield novel theories and insights into central nervous system evolution and diversification, including the vertebrate brain.
More information:
Junko Yaguchi et al, Non-visual photoreceptive brain specification in sea urchin larvae, Nature Communications (2025). DOI: 10.1038/s41467-025-65628-9
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University of Tsukuba
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