A conserved molecular marker for connections between two evolutionarily distinct visual centers
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Sensory systems share common circuit organization motifs across mammalian species, however, anatomical subdivisions show varying degrees of complexity depending on ecological niche and species-specific sensory requirements. While coarse neuroanatomical connections seem preserved within the visual system, it remains unknown if molecularly defined cell-types share a similar degree of conservation, regarding not only their functional properties but also connectivity. Here we analyze the organization, molecular marker expression, and connections between two prominent visual centers, the superior colliculus (SC) and the dorsal lateral geniculate nucleus of the thalamus (dLGN), in the mouse and the tree shrew, a highly visual, diurnal species closely related to primates.
Previous attempts to link molecular markers to subdivisions and connectivity of the dLGN have shown lack of conservation across species, thus preventing the systematic investigation of brain-wide interactions involved in vision. Leveraging recent single-cell and single-nucleus RNA sequencing studies, our results unravel a conserved molecular marker that shows spatial restriction in the dLGN and correlates with the location of connections from the SC in both the mouse and the tree shrew. We extend our findings by confirming the presence of this molecular marker in the human dLGN. These results provide a molecular definition and genetic access point for SC to dLGN connections in the mouse and tree shrew, enabling cell-type specific studies of the parallel processing of visual information.
Significance Statement
While coarse neuroanatomical connections are conserved across mammalian species, their local projection pattern can vary depending on sensory specialization. Furthermore, it remains unknown if these connections are made by homologous molecularly defined cell-types. Our work confirms the conservation of a projection between the superior colliculus and the visual thalamus in the mouse and the tree shrew, which have distinct visual capabilities. We also uncover a genetic access point, unraveling new avenues to understand how these two major visual centers, often studied separately, interact with each other. The remarkable conservation of a molecular marker suggests that despite core anatomical variations and organization principles, the expression of certain genes linked to brain-wide connectivity can be conserved across species.
