Cell types and molecular architecture of the octopus visual system

Abstract

Cephalopods have a remarkable visual system, with a camera-type eye, high acuity vision, and a wide range of sophisticated visual behaviors. However, the cephalopod brain is organized dramatically differently from that of vertebrates, as well as other invertebrates, and little is known regarding the cell types and molecular determinants of their visual system organization beyond neuroanatomical descriptions. Here we present a comprehensive single-cell molecular atlas of the octopus optic lobe, which is the primary visual processing structure in the cephalopod brain. We combined single-cell RNA sequencing with RNA fluorescence in situ hybridization to both identify putative molecular cell types and determine their anatomical and spatial organization within the optic lobe. Our results reveal six major neuronal cell classes identified by neurotransmitter/neuropeptide usage, in addition to non-neuronal and immature neuronal populations. Moreover, we find that additional markers divide these neuronal classes into subtypes with distinct anatomical localizations, revealing cell type diversity and a detailed laminar organization within the optic lobe. We also delineate the immature neurons within this continuously growing tissue into subtypes defined by evolutionarily conserved fate specification genes as well as novel cephalopod- and octopus-specific genes. Together, these findings outline the organizational logic of the octopus visual system, based on functional determinants, laminar identity, and developmental markers/pathways. The resulting atlas presented here delineates the "parts list" of the neural circuits used for vision in octopus, providing a platform for investigations into the development and function of the octopus visual system as well as the evolution of visual processing. HighlightsO_LISingle-cell RNA sequencing coupled with RNA fluorescence in situ hybridization produces a molecular taxonomy of cell types in the octopus visual system. C_LIO_LISix major neuronal cell classes are delineated based on neurotransmitters/neuropeptides, and are further subdivided based on laminar organization and additional marker genes. C_LIO_LIImmature neurons are divided into multiple transcriptional subgroups that correspond to mature cell types, delineated by expression of genes known for their developmental roles in other organisms as well as apparent novel genes. C_LIO_LIThis atlas provides the foundation for future studies of the function, development, and comparative evolution of visual processing in cephalopods. C_LI