Molecular Architecture of the Octopus bimaculoides Central Nervous System
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Date
2024-12-06
Authors
Songco, Jeremea
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Interacting with our environments requires that we appropriately integrate sensory information and convert these inputs into a perception of our surroundings to generate basic and complex behaviors. Traditionally, model organisms, such as nematodes, flies, zebrafish, or even mice, have been used in the laboratory setting to investigate neural circuit formation and function. While these organisms have furthered our understanding of how different cell types wire up to drive complex behavior, there is much to be learned from exploring the brain of non-traditional organisms.
Cephalopods have the largest brain among invertebrates and have a rich catalog of behaviors, including navigating complex underwater environments and rapid body-patterning known as camouflage. While seminal work during the 1960s revealed cellular properties of neurons using the giant squid axon, recent advancements in technology have permitted further characterization of cell types and circuits in a species that is unlike many of those used traditionally in the field of neuroscience. By investigating the brain of these animals, we can begin to understand fundamental mechanisms involved in the formation and function of complex neural circuits.
Unlike model organisms, there are limited tools in genetic manipulation and the field has yet to produce a comprehensive brain atlas bridging anatomical, molecular, and functional properties of cell types in these animals. Therefore, my dissertation sought to develop key resources that will serve as a foundation for such studies once it becomes technically possible. I first contributed to the optimization and usage of functional imaging in an ex vivo preparation of the octopus brain in order to characterize response properties of visually responsive cells in the optic lobe, the main visual center which is a paired brain region that comprises 2/3 of the central nervous system of octopuses. We found evidence for retinotopic organization of responses to light (ON) and dark (OFF) spots, including spatial tuning properties that may be suggestive of environmental demands.
To begin elucidating the diversity of unit responses we revealed in this initial study, I focused on developing a single-cell molecular atlas of the Octopus bimaculoides optic lobe by combining single cell RNA-sequencing (scRNA-seq) with multiplexed fluorescence in situ hybridization (FISH). We identified six classes of mature neuronal cell types in addition to a large population of immature neurons. Our FISH revealed sublaminar organization across the optic lobe, further characterizing the cell types that were initially identified in the 1960s based on morphology. An octopus’ ability to engage in a wide range of visually guided behaviors rests upon the various inputs and outputs the optic lobes have to other structures in the central nervous system. However, there has yet to be published a mapping of these structures as well as an in-depth understanding of the molecular landscape across the central nervous system. Therefore, I sought to develop the first brain-wide gene expression resource for cephalopods by characterizing all of the structures in this species through Hematoxylin & Eoisin (H&E) staining of serial sections of the brain, and I quantified expression for 40 genes, including functional and developmental determinants, across 20 identified brain regions. Together, this work reveals functional and molecular organization in the optic lobe as well as other brain regions, furthering our understanding of how a completely different organism can carry out complex behaviors.
This dissertation includes previously published and unpublished co-authored material.
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Keywords
Cephalopod, Octopus, Vision