Session 2: Evolution of the nervous system – evidence from non-bilateria and protostomia
Cnidaria and the emergence of neurogenesis
Professor Brigitte Galliot, University of Geneva, Switzerland
Abstract
Hydra is a freshwater cnidarian polyp formed of two epithelial cell layers and three stem cell populations, equipped with a sophisticated apical nervous system that includes sensory-motor neurons, ganglia neurons and mechano-sensory cells named nematocytes. All these cells differentiate from interstitial stem cells, and are continuously replaced all along the life of the animals, highlighting the extreme dynamism of neurogenesis in Hydra. Previous studies also showed that animals easily survive the drug- or heatshock-induced elimination of interstitial stem cells that leave the epithelial cells unaffected. Several weeks later such Hydra become “epithelial”, i.e. have lost all their nerve cells, no longer react to touch nor catch their food, but surprisingly still regenerate after bisection, or bud when force-fed. However, Hydra oligactis that can undergo aging, rapidly loose de novo neurogenesis in this context, with dramatic impact on their neurological and developmental behaviours. To assess the role of adult de novo neurogenesis in the maintenance of fitness, regeneration and senescence, we performed quantitative RNAseq analysis on intact, heat-shocked, Hydroxyurea-treated or aging Hydra. We will present and discuss the obtained results in light of evolutionary considerations.
Show speakers
Professor Brigitte Galliot, University of Geneva, Switzerland
Professor Brigitte Galliot, University of Geneva, Switzerland
Brigitte Galliot, MD, PhD, is Associate Professor at the Department of Genetics and Evolution, and Vice-Dean of the Faculty of Sciences, University of Geneva, Switzerland. Her research interest focuses on the identification of the molecular and cellular mechanisms that allow an adult organism to reactivate its developmental programmes(s) after injury or amputation, including de novo neurogenesis. For this, she is using the freshwater cnidarian Hydra polyp as model system. Indeed Hydra can regenerate any missing part of its body after bisection, including its apical nervous system. Basic principles of animal regeneration might be uncovered in this simple animal, as for example the driving force played by injury-induced cell death.
Chair
Dr Erich Jarvis, Duke University and Howard Hughes Medical Institute, USA
Show speakers
Dr Erich Jarvis, Duke University and Howard Hughes Medical Institute, USA
Dr Erich Jarvis, Duke University and Howard Hughes Medical Institute, USA
Dr Erich Jarvis is an Associate Professor of Neurobiology and Howard Hughes Medical Institute (HHMI) Investigator at the Institute for Brain Sciences at Duke University School of Medicine. Since turning down an audition with the Alvin Ailey Dance Theater to pursue science, Erich Jarvis has studied molecular pathways in avian brains as a window into how the brain controls complex behaviour. He has proposed theories about the evolution of vocal production and learning in birds and how it relates to the origins of human language. A graduate of Hunter College, Jarvis conducted research in bacterial molecular genetics with Rivka Rudner. He later earned his PhD in molecular neurobiology and animal behaviour in 1995 at the Rockefeller University, where he did graduate and postdoctoral work in the lab of Fernando Nottebohm. Using a method he termed "behavioural molecular mapping" to determine how a bird's motor activities influence the resulting changes in gene expression in the brain, Jarvis has traced out the brain pathways for vocal learning in three distantly related birds—parrots, hummingbirds, and songbirds—and is now exploring evolutionary connections to understand how these pathways develop. Awards for his work include the NSF’s Alan T. Waterman Award, the NIH Director’s Pioneer Award; his work made Discover's top 100 science discoveries of 2005, and he was chosen one of Popular Science’s Brilliant 10 of 2006.
An option space for early neural evolution
Dr Gáspár Jékely, Living Systems Institute, University of Exeter, UK
Abstract
The origin of nervous systems has traditionally been discussed within two conceptual frameworks. Input-output models stress the sensory-motor aspects of nervous systems, while internal coordination models emphasise the role of nervous systems in coordinating large-scale body movements. Here we consider both frameworks and apply them to describe aspects of each of three main groups of phenomena that nervous systems control: behaviour, physiology and development. We argue that both frameworks and all three aspects of nervous system function need to be considered for a comprehensive discussion of nervous system origins. This broad mapping of the option space enables a more comprehensive overview of the many influences and constraints that may have played a role in the evolution of the first nervous systems.
Show speakers
Dr Gáspár Jékely, Living Systems Institute, University of Exeter, UK
Dr Gáspár Jékely, Living Systems Institute, University of Exeter, UK
Gáspár Jékely studied Biology and obtained his PhD in 1999 at the Eötvös Loránd Universities in Budapest. He then worked as a postdoc at the EMBL, Heidelberg in the laboratory of Pernille Rorth and then Detlev Arendt. Between 2007-2017 he was a group leader at the Max Planck Institute for Developmental Biology in Tübingen, Germany. He moved to the Living Systems Institute at the University of Exeter as Professor of Neuroscience in 2017. His research interests include the structure, function and evolution of neural circuits in marine ciliated larvae and the origin and early evolution of nervous systems.
Genomic bases of multiple origins and parallel evolution of neurons and synapses: insights from ctenophores and molluscs
Professor Leonid Moroz, University of Florida, USA
Abstract
Advances in Omics and their implementations to basal metazoan clades (Ctenophora, Porifera, Placozoa, Cnidaria, Bilateria) resulted to revisions of the animal phylogeny and hypotheses of neural evolution. Our analysis suggests that both neurons and synapses evolved independently from different cell lineages recruiting the ancestral machinery for secretion and reception developed in early eukaryotes.
The first case is the independent origin of neurons in ctenophores as evidenced by our combined genomic, proteomic, metabolomics and physiological studies on four ctenophore species (Pleurobrachia, Mnemiopsis, Bolinopsis and Beroe). Historically, temporal differentiation of cellular phenotypes found in unicellular eukaryotes (as result of their complex life cycles) was substituted and extended by spatial differentiation in metazoans leading to a greater diversity of cell types. Some components of synaptic and neuronal machinery might represent examples of convergent evolution.
The second remarkable example is the parallel origins of cell lineages supporting intercellular signaling using various transmitters. Combining data from 10+ phyla, including single-neuron RNA-seq and, unbiased single-cell epigenomic profiling, we will discuss how recruitment of various molecular modules together with environmental constrains might lead to independent origins of neurons and synapses across distinct animal clades.
Phylogenetic reconstructions also suggest that neuronal centralisation and mosaic formation of complex brains evolved at least 12 times across the animal kingdom, with 5 independent centralisation events in the molluscan clade including cephalopods - the ‘primates of the sea’. Thus, we define neurons as a functional rather than a genetic category. Neurons are polarised secretory cells specialised for directional propagation of electrical signals leading to release of intracellular messengers – features that enable them to transmit information, primarily chemical in nature, beyond their immediate neighbours without affecting all intervening cells en route. However, using an array of molecular markers within some animal lineages, especially in molluscs, one can recognise homologous neuronal lineages. These examples and criteria for homologisation of distinct cell lineages will be discussed toward reconstruction of natural classification of neurons or NeuroSystematics.
Show speakers
Professor Leonid Moroz, University of Florida, USA
Professor Leonid Moroz, University of Florida, USA
Moroz earned his PhD in comparative physiology from the Institute of Developmental Biology in Moscow (1989). He was an international HHMI scholar. His postdoctoral research was done with Dr William Winlow at the University of Leeds, UK and with Dr Rhanor Gillette at the University of Illinois, Urbana, USA. He joined University of Florida in 1998.
Brain & Memory Genomics: Moroz’s laboratory focuses on the mechanisms underlying the design of nervous systems and develops innovative approaches to study the genomic basis of neuronal identity and plasticity. His team pursues understanding what makes a neuron a neuron and why they differ so from each other; how they maintain such precise connections between each other; how this fixed wiring results in such enormous neuronal plasticity; and how this contributes to learning, memory mechanisms, aging and regeneration.
Ocean & Space Genomics: The second groups of projects deal with exploration of life frontiers and evolution. Here, Moroz’s lab is focusing on global biodiversity targeting little/under investigated lineages of animals (e.g. sequencing genomes of ctenophores) and their adaptation to extreme environments from cold Antarctic to Space. Moroz has performed a number of oceanic expeditions across the globe (his sequencing-on-ship, Ship-Seq, attracted world-wide attention) and collaborated with NASA and Russian Space Programs to study adaptations to microgravity including orbit missions.
Moroz’s work has been published and covered widely with more than 130 papers including Nature, Science, Cell, Neuron, PNAS, etc.
Where is my mind? How sponges and placozoans may have lost neural cell types
Dr Joseph Ryan, University of Florida, USA
Abstract
For over 150 years, it was thought that sponges were the sister group to all other animals (if they were animals at all) and that the sponge body plan represented a primitive stage in animal evolution. Similarly, it has long been thought that placozoans represent a basic body type that has endured hundreds of million years of evolution. Recent phylogenetic analyses of animal genomes and transcriptomes, however, have challenged these ideas, suggesting that ctenophores are the sister group to all other animals and implying that sophisticated cell types like neurons either evolved multiple times or were lost during the evolution of sponges and placozoans. Thus far, the far more preferred hypothesis appears to be that neural cell types evolved multiple times. I argue that historical bias may be playing a role in the rejection of cell-type loss as an explanation of the data, and that a novel analysis of evidence in light of this hypothesis is both compelling and revealing.
Show speakers
Dr Joseph Ryan, University of Florida, USA
Dr Joseph Ryan, University of Florida, USA
Joseph Ryan is Assistant Professor of Biology at the Whitney Laboratory for Marine Bioscience (University of Florida) in the United States. His research concentrates on the evolution of animal genomes with a particular focus on how changes in animal genomes have influenced developmental processes over time. He has an AA in general studies from Essex Community College in Baltimore, a BS in Computer Science from the University of Maryland University College, and a PhD in Bioinformatics from Boston University. He did a postdoc at the National Human Genome Research Institute and at the Sars Centre for Marine Molecular Biology before starting his present position in 2014.
Development and structure of anthozoan nervous systems
Professor Ulrich Technau, University of Vienna, Austria
Abstract
Cnidarians are the sister group of Bilateria and can therefore provide important insights into the evolution of key bilaterian traits. One of the hallmarks of bilaterians is the central nervous system. Cnidarians do not possess a central nervous system or a brain, and the nervous system of cnidarians has often been referred to as "diffuse". However, regional accumulations of neurons or nerve rings for instance found at the margin of jellyfish, as well as patterning of specific neuronal subtypes expressing different neurotransmitters suggest a certain level of complexity. Neurogenesis has been mainly studied in the hydrozoan Hydra and in the sea anemone Nematostella vectensis. While in Hydra, neurons arise from multipotent interstitial stem cells, such stem cells have not been found in Nematostella. Instead, in this organism neurons appear to differentiate directly from epithelial cells. I will discuss the similarities and differences of nervous system formation in the context of patterning of the body plan and compare it with bilaterians.
Show speakers
Professor Ulrich Technau, University of Vienna, Austria
Professor Ulrich Technau, University of Vienna, Austria
Ulrich Technau studied Biology at the Universities of Würzburg, Mainz, Toulouse and Munich. He obtained his PhD at the University of Frankfurt in 1995 with his work on head patterning and neuronal differentiation in Hydra. He then worked as a postdoc at the University of California at Irvine and returned to the Darmstadt University of Technology, Germany in 1998, where he obtained his habilitation. From 2004-2007 he was a group leader at the Sars Centre for Marine Molecular Biology in Bergen, Norway before accepting an offer as a full Professor for Developmental Biology at the University of Vienna, Austria. His research interests include the evolution of developmental processes and key bilaterian traits by investigating different Cnidaria, the sister group of the Bilateria. He integrates developmental, molecular and genomic approaches to address these questions.