Evolution of the nervous system in bilateria
As a ‘living fossil’, Platynereis represents an ideal connecting link between vertebrates and the fast evolving protostome models, Drosophila and Caenorhabditis
By studying and comparing simple marine organisms, the Arendt group looks to understand the origin and evolution of our central nervous system.
Previous and current research
We are intrigued by one of the great remaining mysteries in animal evolution: how did our central nervous system (CNS) come into being? What did it first look like and how did it function? We are especially interested in the CNS of an extinct animal, known as Urbilateria, which lived some 600 million years ago in the ocean – the last common ancestor of humans, flies and most other ‘higher’ animals that live today.
Our lab has chosen to investigate a new molecular animal model, the marine annelid Platynereis dumerilii. Genomic resources and molecular techniques have been generated that make it a model marine invertebrate for ocean biology and for organismal systems biology. Platynereis is amenable to high-throughput imaging techniques and functional interference approaches (first genetic knock-out lines have been generated). With the recent development of the PrImR (Profiling by Image Registration) resource, it is the first animal model for which gene expression profiling data can be obtained in cellular resolution for the whole organism. We have discovered that the Platynereis’ brain harbours sensory-associative brain parts and a neurosecretory brain centre that correspond to the vertebrate pallium and hypothalamus respectively – findings that revolutionise our understanding of brain evolution. A clear picture is emerging that the Platynereis brain harbours many cell types so far known only for the vertebrates, but in a much more simple and different overall arrangement.
To broaden our comparative approach, we study two other model species (amphioxus and Nematostella), representing distinct divisions of the animal kingdom: chordates and cnidarians. Amphioxus has a very simple brain, uniting invertebrate- and vertebrate-like features. The Nematostella nervous system is very simple and thus represents a good proxy for a very early stage of nervous system evolution.
Future projects and goals
Our aim is to gain a systems view of the Platynereis brain and to track the evolutionary history of all constituent cell types by identifying and investigating their evolutionary counterparts in sea anemone and amphioxus. This will involve investigations of cell type-specific gene regulatory networks as well as neurobiological and behavioural approaches.In collaboration with the Janelia Farm Research Centre, we will extend the PrImR protocol to key stages of the Platynereis larval development and life cycle, in order to generate the first cellular resolution expression atlas for a whole animal (early developmental as well as differentiation stages).
In 2012, we began an ERC-funded project, ‘BrainEvoDevo’, to generate a neuron type atlas of the annelid larval brain, combining neuronal morphologies, axonal projections and cellular expression profiling for an entire bilaterian brain. Building on the atlas, we will dissect Platynereis chemosensory-motor forebrain circuits, by laser ablation of GFP-labelled single neurons, gene knockout studies and behavioural assays based on microfluidics. Our aim is to explore duplication, divergence and expansion of neural circuits in CNS development and evolution.
We are also interested in exploring population genetics and the variability of development and differention in different habitats and we are collecting strains of Platynereis and amphioxus as part of the TARA Oceans expedition and EMBL oceans team.
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