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Ramirez MD, Bui TN, Katz PS. Cellular-resolution gene expression mapping reveals organization in the head ganglia of the gastropod, Berghia stephanieae. J Comp Neurol 2024; 532:e25628. [PMID: 38852042 PMCID: PMC11198006 DOI: 10.1002/cne.25628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2023] [Revised: 04/25/2024] [Accepted: 05/09/2024] [Indexed: 06/10/2024]
Abstract
Gastropod molluscs such as Aplysia, Lymnaea, and Tritonia have been important for determining fundamental rules of motor control, learning, and memory because of their large, individually identifiable neurons. Yet only a small number of gastropod neurons have known molecular markers, limiting the ability to establish brain-wide structure-function relations. Here we combine high-throughput, single-cell RNA sequencing with in situ hybridization chain reaction in the nudibranch Berghia stephanieae to identify and visualize the expression of markers for cell types. Broad neuronal classes were characterized by genes associated with neurotransmitters, like acetylcholine, glutamate, serotonin, and GABA, as well as neuropeptides. These classes were subdivided by other genes including transcriptional regulators and unannotated genes. Marker genes expressed by neurons and glia formed discrete, previously unrecognized regions within and between ganglia. This study provides the foundation for understanding the fundamental cellular organization of gastropod nervous systems.
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Affiliation(s)
| | - Thi N. Bui
- Department of Biology, University of Massachusetts Amherst
| | - Paul S. Katz
- Department of Biology, University of Massachusetts Amherst
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2
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Goodheart JA, Rio RA, Taraporevala NF, Fiorenza RA, Barnes SR, Morrill K, Jacob MAC, Whitesel C, Masterson P, Batzel GO, Johnston HT, Ramirez MD, Katz PS, Lyons DC. A chromosome-level genome for the nudibranch gastropod Berghia stephanieae helps parse clade-specific gene expression in novel and conserved phenotypes. BMC Biol 2024; 22:9. [PMID: 38233809 PMCID: PMC10795318 DOI: 10.1186/s12915-024-01814-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Accepted: 01/03/2024] [Indexed: 01/19/2024] Open
Abstract
BACKGROUND How novel phenotypes originate from conserved genes, processes, and tissues remains a major question in biology. Research that sets out to answer this question often focuses on the conserved genes and processes involved, an approach that explicitly excludes the impact of genetic elements that may be classified as clade-specific, even though many of these genes are known to be important for many novel, or clade-restricted, phenotypes. This is especially true for understudied phyla such as mollusks, where limited genomic and functional biology resources for members of this phylum have long hindered assessments of genetic homology and function. To address this gap, we constructed a chromosome-level genome for the gastropod Berghia stephanieae (Valdés, 2005) to investigate the expression of clade-specific genes across both novel and conserved tissue types in this species. RESULTS The final assembled and filtered Berghia genome is comparable to other high-quality mollusk genomes in terms of size (1.05 Gb) and number of predicted genes (24,960 genes) and is highly contiguous. The proportion of upregulated, clade-specific genes varied across tissues, but with no clear trend between the proportion of clade-specific genes and the novelty of the tissue. However, more complex tissue like the brain had the highest total number of upregulated, clade-specific genes, though the ratio of upregulated clade-specific genes to the total number of upregulated genes was low. CONCLUSIONS Our results, when combined with previous research on the impact of novel genes on phenotypic evolution, highlight the fact that the complexity of the novel tissue or behavior, the type of novelty, and the developmental timing of evolutionary modifications will all influence how novel and conserved genes interact to generate diversity.
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Affiliation(s)
- Jessica A Goodheart
- Division of Invertebrate Zoology, American Museum of Natural History, New York, NY, USA.
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA.
| | - Robin A Rio
- Bioengineering Department, Stanford University, Stanford, CA, USA
| | - Neville F Taraporevala
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
- Department of Wildland Resources, Utah State University, Logan, UT, USA
| | - Rose A Fiorenza
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Seth R Barnes
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Kevin Morrill
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Mark Allan C Jacob
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Carl Whitesel
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Park Masterson
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Grant O Batzel
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Hereroa T Johnston
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - M Desmond Ramirez
- Department of Biology, University of Massachusetts Amherst, Amherst, MA, USA
- Institute of Neuroscience, University of Oregon, Eugene, OR, USA
| | - Paul S Katz
- Department of Biology, University of Massachusetts Amherst, Amherst, MA, USA
| | - Deirdre C Lyons
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA.
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3
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Goodheart JA, Rio RA, Taraporevala NF, Fiorenza RA, Barnes SR, Morrill K, Jacob MAC, Whitesel C, Masterson P, Batzel GO, Johnston HT, Ramirez MD, Katz PS, Lyons DC. A chromosome-level genome for the nudibranch gastropod Berghia stephanieae helps parse clade-specific gene expression in novel and conserved phenotypes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.04.552006. [PMID: 38014205 PMCID: PMC10680569 DOI: 10.1101/2023.08.04.552006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
How novel phenotypes originate from conserved genes, processes, and tissues remains a major question in biology. Research that sets out to answer this question often focuses on the conserved genes and processes involved, an approach that explicitly excludes the impact of genetic elements that may be classified as clade-specific, even though many of these genes are known to be important for many novel, or clade-restricted, phenotypes. This is especially true for understudied phyla such as mollusks, where limited genomic and functional biology resources for members of this phylum has long hindered assessments of genetic homology and function. To address this gap, we constructed a chromosome-level genome for the gastropod Berghia stephanieae (Valdés, 2005) to investigate the expression of clade-specific genes across both novel and conserved tissue types in this species. The final assembled and filtered Berghia genome is comparable to other high quality mollusk genomes in terms of size (1.05 Gb) and number of predicted genes (24,960 genes), and is highly contiguous. The proportion of upregulated, clade-specific genes varied across tissues, but with no clear trend between the proportion of clade-specific genes and the novelty of the tissue. However, more complex tissue like the brain had the highest total number of upregulated, clade-specific genes, though the ratio of upregulated clade-specific genes to the total number of upregulated genes was low. Our results, when combined with previous research on the impact of novel genes on phenotypic evolution, highlight the fact that the complexity of the novel tissue or behavior, the type of novelty, and the developmental timing of evolutionary modifications will all influence how novel and conserved genes interact to generate diversity.
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Affiliation(s)
- Jessica A. Goodheart
- Division of Invertebrate Zoology, American Museum of Natural History, New York, NY USA
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Robin A. Rio
- Bioengineering Department, Stanford University, Stanford, CA, USA
| | - Neville F. Taraporevala
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
- Department of Wildland Resources, Utah State University, Logan, UT, USA
| | - Rose A. Fiorenza
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Seth R. Barnes
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Kevin Morrill
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Mark Allan C. Jacob
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Carl Whitesel
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Park Masterson
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Grant O. Batzel
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Hereroa T. Johnston
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - M. Desmond Ramirez
- Department of Biology, University of Massachusetts Amherst, Amherst, MA, USA
| | - Paul S. Katz
- Department of Biology, University of Massachusetts Amherst, Amherst, MA, USA
| | - Deirdre C. Lyons
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
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4
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Newcomb JM, Todd K, Buhl E. Editorial: Invertebrate neurophysiology-of currents, cells, and circuits. Front Neurosci 2023; 17:1303574. [PMID: 37901422 PMCID: PMC10613048 DOI: 10.3389/fnins.2023.1303574] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 10/03/2023] [Indexed: 10/31/2023] Open
Affiliation(s)
- James M. Newcomb
- Department of Biology and Health Science, New England College, Henniker, NH, United States
| | - Krista Todd
- Neuroscience, Westminster University, Salt Lake City, UT, United States
| | - Edgar Buhl
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
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5
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Blitz DM. Neural circuit regulation by identified modulatory projection neurons. Front Neurosci 2023; 17:1154769. [PMID: 37008233 PMCID: PMC10063799 DOI: 10.3389/fnins.2023.1154769] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Accepted: 03/01/2023] [Indexed: 03/19/2023] Open
Abstract
Rhythmic behaviors (e.g., walking, breathing, and chewing) are produced by central pattern generator (CPG) circuits. These circuits are highly dynamic due to a multitude of input they receive from hormones, sensory neurons, and modulatory projection neurons. Such inputs not only turn CPG circuits on and off, but they adjust their synaptic and cellular properties to select behaviorally relevant outputs that last from seconds to hours. Similar to the contributions of fully identified connectomes to establishing general principles of circuit function and flexibility, identified modulatory neurons have enabled key insights into neural circuit modulation. For instance, while bath-applying neuromodulators continues to be an important approach to studying neural circuit modulation, this approach does not always mimic the neural circuit response to neuronal release of the same modulator. There is additional complexity in the actions of neuronally-released modulators due to: (1) the prevalence of co-transmitters, (2) local- and long-distance feedback regulating the timing of (co-)release, and (3) differential regulation of co-transmitter release. Identifying the physiological stimuli (e.g., identified sensory neurons) that activate modulatory projection neurons has demonstrated multiple “modulatory codes” for selecting particular circuit outputs. In some cases, population coding occurs, and in others circuit output is determined by the firing pattern and rate of the modulatory projection neurons. The ability to perform electrophysiological recordings and manipulations of small populations of identified neurons at multiple levels of rhythmic motor systems remains an important approach for determining the cellular and synaptic mechanisms underlying the rapid adaptability of rhythmic neural circuits.
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6
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Taraporevala NF, Lesoway MP, Goodheart JA, Lyons DC. Precocious Sperm Exchange in the Simultaneously Hermaphroditic Nudibranch, Berghia stephanieae. Integr Org Biol 2022; 4:obac030. [PMID: 36089995 PMCID: PMC9449679 DOI: 10.1093/iob/obac034] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 06/10/2022] [Accepted: 07/28/2022] [Indexed: 11/15/2022] Open
Abstract
Sexual systems vary greatly across molluscs. This diversity includes simultaneous hermaphroditism, with both sexes functional at the same time. Most nudibranch molluscs are thought to be simultaneous hermaphrodites, but detailed studies of reproductive development and timing remain rare as most species cannot be cultured in the lab. The aeolid nudibranch, Berghia stephanieae, is one such species that can be cultured through multiple generations on the benchtop. We studied B. stephanieae reproductive timing to establish when animals first exchange sperm and how long sperm can be stored. We isolated age- and size-matched individuals at sequential timepoints to learn how early individuals can exchange sperm. Individuals isolated at 10 weeks post initial feeding (wpf; ∼13 weeks postlaying [wpl]) can produce fertilized eggs. This is 6 weeks before animals first lay egg masses, indicating that sperm exchange occurs well before individuals are capable of laying eggs. Our results indicate that male gonads become functional for animals between 6 mm (∼6 wpf, ∼9 wpl) and 9 mm (∼12 wpf, ∼15 wpl) in length. That is much smaller (and sooner) than the size (and age) of individuals at first laying (12–19 mm; ∼16 wpf, ∼19 wpl), indicating that male and female functions do not develop simultaneously. We also tracked the number of fertilized eggs in each egg mass, which remained steady for the first 10–15 egg masses, followed by a decline to near-to-no fertilization. This dataset provides insights into the precise timing of the onset of functionality of the male and female reproductive systems in B. stephanieae. These data contribute to a broader understanding of reproductive development and the potential for understanding the evolution of diverse sexual systems in molluscs.
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Affiliation(s)
- Neville F Taraporevala
- Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Maryna P Lesoway
- Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Jessica A Goodheart
- Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Deirdre C Lyons
- Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, CA 92093, USA
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7
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Tamvacakis AN, Lillvis JL, Sakurai A, Katz PS. The Consistency of Gastropod Identified Neurons Distinguishes Intra-Individual Plasticity From Inter-Individual Variability in Neural Circuits. Front Behav Neurosci 2022; 16:855235. [PMID: 35309684 PMCID: PMC8928192 DOI: 10.3389/fnbeh.2022.855235] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Accepted: 02/07/2022] [Indexed: 11/13/2022] Open
Abstract
Gastropod mollusks are known for their large, individually identifiable neurons, which are amenable to long-term intracellular recordings that can be repeated from animal to animal. The constancy of individual neurons can help distinguish state-dependent or temporal variation within an individual from actual variability between individual animals. Investigations into the circuitry underlying rhythmic swimming movements of the gastropod species, Tritonia exsulans and Pleurobranchaea californica have uncovered intra- and inter-individual variability in synaptic connectivity and serotonergic neuromodulation. Tritonia has a reliably evoked escape swim behavior that is produced by a central pattern generator (CPG) composed of a small number of identifiable neurons. There is apparent individual variability in some of the connections between neurons that is inconsequential for the production of the swim behavior under normal conditions, but determines whether that individual can swim following a neural lesion. Serotonergic neuromodulation of synaptic strength intrinsic to the CPG creates neural circuit plasticity within an individual and contributes to reorganization of the network during recovery from injury and during learning. In Pleurobranchaea, variability over time in the modulatory actions of serotonin and in expression of serotonin receptor genes in an identified neuron directly reflects variation in swimming behavior. Tracking behavior and electrophysiology over hours to days was necessary to identify the functional consequences of these intra-individual, time-dependent variations. This work demonstrates the importance of unambiguous neuron identification, properly assessing the animal and network states, and tracking behavior and physiology over time to distinguish plasticity within the same animal at different times from variability across individual animals.
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Affiliation(s)
| | | | - Akira Sakurai
- Neuroscience Institute, Georgia State University, Atlanta, GA, United States
| | - Paul S. Katz
- Department of Biology, University of Massachusetts Amherst, Amherst, MA, United States
- *Correspondence: Paul S. Katz,
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8
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Lee CA, Romanova EV, Southey BR, Gillette R, Sweedler JV. Comparative Analysis of Neuropeptides in Homologous Interneurons and Prohormone Annotation in Nudipleuran Sea Slugs. Front Physiol 2022; 12:809529. [PMID: 35002782 PMCID: PMC8735849 DOI: 10.3389/fphys.2021.809529] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Accepted: 12/02/2021] [Indexed: 02/06/2023] Open
Abstract
Despite substantial research on neuronal circuits in nudipleuran gastropods, few peptides have been implicated in nudipleuran behavior. In this study, we expanded the understanding of peptides in this clade, using three species with well-studied nervous systems, Hermissenda crassicornis, Melibe leonina, and Pleurobranchaea californica. For each species, we performed sequence homology analysis of de novo transcriptome predictions to identify homologs to 34 of 36 prohormones previously characterized in the gastropods Aplysia californica and Lymnaea stagnalis. We then used single-cell mass spectrometry to characterize peptide profiles in homologous feeding interneurons: the multifunctional ventral white cell (VWC) in P. californica and the small cardioactive peptide B large buccal (SLB) cells in H. crassicornis and M. leonina. The neurons produced overlapping, but not identical, peptide profiles. The H. crassicornis SLB cells expressed peptides from homologs to the FMRFamide (FMRFa), small cardioactive peptide (SCP), LFRFamide (LFRFa), and feeding circuit activating peptides prohormones. The M. leonina SLB cells expressed peptides from homologs to the FMRFa, SCP, LFRFa, and MIP-related peptides prohormones. The VWC, previously shown to express peptides from the FMRFa and QNFLa (a homolog of A. californica pedal peptide 4) prohormones, was shown to also contain SCP peptides. Thus, each neuron expressed peptides from the FMRFa and SCP families, the H. crassicornis and M. leonina SLB cells expressed peptides from the LFRFa family, and each neuron contained peptides from a prohormone not found in the others. These data suggest each neuron performs complex co-transmission, which potentially facilitates a multifunctional role in feeding. Additionally, the unique feeding characteristics of each species may relate, in part, to differences in the peptide profiles of these neurons. These data add chemical insight to enhance our understanding of the neuronal basis of behavior in nudipleurans and other gastropods.
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Affiliation(s)
- Colin A Lee
- Neuroscience Program, University of Illinois Urbana-Champaign, Urbana, IL, United States
| | - Elena V Romanova
- Neuroscience Program, University of Illinois Urbana-Champaign, Urbana, IL, United States.,Department of Chemistry, University of Illinois Urbana-Champaign, Urbana, IL, United States
| | - Bruce R Southey
- Department of Animal Sciences, University of Illinois Urbana-Champaign, Urbana, IL, United States
| | - Rhanor Gillette
- Neuroscience Program, University of Illinois Urbana-Champaign, Urbana, IL, United States.,Department of Molecular and Integrative Physiology, University of Illinois Urbana-Champaign, Urbana, IL, United States
| | - Jonathan V Sweedler
- Neuroscience Program, University of Illinois Urbana-Champaign, Urbana, IL, United States.,Department of Chemistry, University of Illinois Urbana-Champaign, Urbana, IL, United States
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9
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Whole-body integration of gene expression and single-cell morphology. Cell 2021; 184:4819-4837.e22. [PMID: 34380046 PMCID: PMC8445025 DOI: 10.1016/j.cell.2021.07.017] [Citation(s) in RCA: 37] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 05/05/2021] [Accepted: 07/14/2021] [Indexed: 01/10/2023]
Abstract
Animal bodies are composed of cell types with unique expression programs that implement their distinct locations, shapes, structures, and functions. Based on these properties, cell types assemble into specific tissues and organs. To systematically explore the link between cell-type-specific gene expression and morphology, we registered an expression atlas to a whole-body electron microscopy volume of the nereid Platynereis dumerilii. Automated segmentation of cells and nuclei identifies major cell classes and establishes a link between gene activation, chromatin topography, and nuclear size. Clustering of segmented cells according to gene expression reveals spatially coherent tissues. In the brain, genetically defined groups of neurons match ganglionic nuclei with coherent projections. Besides interneurons, we uncover sensory-neurosecretory cells in the nereid mushroom bodies, which thus qualify as sensory organs. They furthermore resemble the vertebrate telencephalon by molecular anatomy. We provide an integrated browser as a Fiji plugin for remote exploration of all available multimodal datasets. A cellular atlas integrates gene expression and ultrastructure for an entire annelid Morphometry of all segmented cells, nuclei, and chromatin categorizes cell classes Molecular anatomy and projectome of head ganglionic nuclei and mushroom bodies An open-source browser for multimodal big image data exploration and analysis
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10
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Identification and classification of innexin gene transcripts in the central nervous system of the terrestrial slug Limax valentianus. PLoS One 2021; 16:e0244902. [PMID: 33857131 PMCID: PMC8049302 DOI: 10.1371/journal.pone.0244902] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Accepted: 03/09/2021] [Indexed: 12/20/2022] Open
Abstract
Intercellular gap junction channels and single-membrane channels have been reported to regulate electrical synapse and the brain function. Innexin is known as a gap junction-related protein in invertebrates and is involved in the formation of intercellular gap junction channels and single-cell membrane channels. Multiple isoforms of innexin protein in each species enable the precise regulation of channel function. In molluscan species, sequence information of innexins is still limited and the sequences of multiple innexin isoforms have not been classified. This study examined the innexin transcripts expressed in the central nervous system of the terrestrial slug Limax valentianus and identified 16 transcripts of 12 innexin isoforms, including the splicing variants. We performed phylogenetic analysis and classified the isoforms with other molluscan innexin sequences. Next, the phosphorylation, N-glycosylation, and S-nitrosylation sites were predicted to characterize the innexin isoforms. Further, we identified 16 circular RNA sequences of nine innexin isoforms in the central nervous system of Limax. The identification and classification of molluscan innexin isoforms provided novel insights for understanding the regulatory mechanism of innexin in this phylum.
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11
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Heath-Heckman E, Yoo S, Winchell C, Pellegrino M, Angstadt J, Lammardo VB, Bautista D, De-Miguel FF, Weisblat D. Transcriptional profiling of identified neurons in leech. BMC Genomics 2021; 22:215. [PMID: 33765928 PMCID: PMC7992859 DOI: 10.1186/s12864-021-07526-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 03/11/2021] [Indexed: 12/13/2022] Open
Abstract
Background While leeches in the genus Hirudo have long been models for neurobiology, the molecular underpinnings of nervous system structure and function in this group remain largely unknown. To begin to bridge this gap, we performed RNASeq on pools of identified neurons of the central nervous system (CNS): sensory T (touch), P (pressure) and N (nociception) neurons; neurosecretory Retzius cells; and ganglia from which these four cell types had been removed. Results Bioinformatic analyses identified 3565 putative genes whose expression differed significantly among the samples. These genes clustered into 9 groups which could be associated with one or more of the identified cell types. We verified predicted expression patterns through in situ hybridization on whole CNS ganglia, and found that orthologous genes were for the most part similarly expressed in a divergent leech genus, suggesting evolutionarily conserved roles for these genes. Transcriptional profiling allowed us to identify candidate phenotype-defining genes from expanded gene families. Thus, we identified one of eight hyperpolarization-activated cyclic-nucleotide gated (HCN) channels as a candidate for mediating the prominent sag current in P neurons, and found that one of five inositol triphosphate receptors (IP3Rs), representing a sub-family of IP3Rs absent from vertebrate genomes, is expressed with high specificity in T cells. We also identified one of two piezo genes, two of ~ 65 deg/enac genes, and one of at least 16 transient receptor potential (trp) genes as prime candidates for involvement in sensory transduction in the three distinct classes of leech mechanosensory neurons. Conclusions Our study defines distinct transcriptional profiles for four different neuronal types within the leech CNS, in addition to providing a second ganglionic transcriptome for the species. From these data we identified five gene families that may facilitate the sensory capabilities of these neurons, thus laying the basis for future work leveraging the strengths of the leech system to investigate the molecular processes underlying and linking mechanosensation, cell type specification, and behavior. Supplementary Information The online version contains supplementary material available at 10.1186/s12864-021-07526-0.
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Affiliation(s)
- Elizabeth Heath-Heckman
- Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA, USA. .,Current address: Department of Integrative Biology, Michigan State University, East Lansing, MI, USA.
| | - Shinja Yoo
- Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA, USA
| | - Christopher Winchell
- Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA, USA
| | - Maurizio Pellegrino
- Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA, USA.,Current address: Invitae Corporation, San Francisco, CA, USA
| | - James Angstadt
- Department of Biology, Siena College, Loudonville, New York, NY, USA
| | | | - Diana Bautista
- Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA, USA
| | - Francisco F De-Miguel
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - David Weisblat
- Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA, USA.
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12
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Expanding evolutionary neuroscience: insights from comparing variation in behavior. Neuron 2021; 109:1084-1099. [PMID: 33609484 DOI: 10.1016/j.neuron.2021.02.002] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Revised: 01/25/2021] [Accepted: 01/28/2021] [Indexed: 01/01/2023]
Abstract
Neuroscientists have long studied species with convenient biological features to discover how behavior emerges from conserved molecular, neural, and circuit level processes. With the advent of new tools, from viral vectors and gene editing to automated behavioral analyses, there has been a recent wave of interest in developing new, "nontraditional" model species. Here, we advocate for a complementary approach to model species development, that is, model clade development, as a way to integrate an evolutionary comparative approach with neurobiological and behavioral experiments. Capitalizing on natural behavioral variation in and investing in experimental tools for model clades will be a valuable strategy for the next generation of neuroscience discovery.
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13
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Command or Obey? Homologous Neurons Differ in Hierarchical Position for the Generation of Homologous Behaviors. J Neurosci 2019; 39:6460-6471. [PMID: 31209170 DOI: 10.1523/jneurosci.3229-18.2019] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2018] [Revised: 04/20/2019] [Accepted: 05/08/2019] [Indexed: 11/21/2022] Open
Abstract
In motor systems, higher-order neurons provide commands to lower-level central pattern generators (CPGs) that autonomously produce rhythmic motor patterns. Such hierarchical organization is often thought to be inherent in the anatomical position of the neurons. Here, however, we report that a neuron that is member of a CPG in one species acts as a higher-order neuron in another species. In the nudibranch mollusc, Melibe leonina, swim interneuron 1 (Si1) is in the CPG underlying swimming, firing rhythmic bursts of action potentials as part of the swim motor pattern. We found that its homolog in another nudibranch, Dendronotus iris, serves as a neuromodulatory command neuron for the CPG of a homologous swimming behavior. In Dendronotus, Si1 fired irregularly throughout the swim motor pattern. The burst and spike frequencies of Dendronotus swim CPG neurons correlated with Si1 firing frequency. Si1 activity was both necessary and sufficient for the initiation and maintenance of the swim motor pattern. Each Si1 was electrically coupled to all of the CPG neurons and made monosynaptic excitatory synapses with both Si3s. Si1 also bilaterally potentiated the excitatory synapse from Si3 to Si2. "Virtual neuromodulation" of both Si3-to-Si2 synapses using dynamic clamp combined with depolarization of both Si3s mimicked the effects of Si1 stimulation on the swim motor pattern. Thus, in Dendronotus, Si1 is a command neuron that turns on, maintains, and accelerates the motor pattern through synaptic and neuromodulatory actions, thereby differing from its homolog in Melibe in its functional position in the motor hierarchy.SIGNIFICANCE STATEMENT Cross-species comparisons of motor system organization can provide fundamental insights into their function and origin. Central pattern generators (CPGs) are lower in the functional hierarchy than the neurons that initiate and modulate their activity. This functional hierarchy is often reflected in neuroanatomical organization. This paper definitively shows that an identified cerebral ganglion neuron that is a member of a CPG underlying swimming in one nudibranch species serves as a command neuron for the same behavior in another species. We describe and test the synaptic and neuromodulatory mechanisms by which the command neuron initiates and accelerates rhythmic motor patterns. Thus, the functional position of neurons in a motor hierarchy can shift from one level to another over evolutionary time.
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