Arendt Group
Evolution of the central nervous system in Bilateria
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 existence? What did it look like at first and how did it function? We are especially interested in the CNS of an extinct animal known as Urbilateria, the last common ancestor of humans, flies and most other ‘higher’ animals that live today, which lived some 600 million years ago in the ocean.
Our lab has chosen to investigate a new molecular animal model, the marine annelid Platynereis dumerilii. As a ‘living fossil’, Platynereis represents an ideal connecting link between vertebrates and the fast evolving protostome models, Drosophila and Caenorhabditis. Genomic resources and molecular techniques have been generated that make it a model marine invertebrate for ocean biology and for organismal systems biology. As characteristic for the Platynereis life cycle with different stages exploring different ecological niches, environmental influences impact directly on the organismal state (eco-devo) or are sensed via the nervous system (organismal neurobiology) and are reflected by the variation on genome, transcriptome or any other level of the cellome.
Platynereis is amenable to high-throughput imaging techniques and functional interference approaches. For example, first genetic knock-out lines have been generated. With the recent development of the PrImR (Profiling by Image Registration) resource, Platynereis has become the first animal model for which gene expression profiling data can be obtained in cellular resolution for the whole organism. Building on these resources, 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. These findings revolutionise our current understanding of brain evolution.
In an attempt to broaden our comparative approach, we have introduced two new model species to the lab, the lancelet amphioxus and the sea anemone 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 brain evolution.
Future projects and goals
A clear picture is emerging that the Platynereis brain harbours many cell types so far known only in vertebrates, but in a much more simple and different overall arrangement. This makes it an attractive goal to elucidate the functioning of these cell types in the ancient marine environment in order to gain insight into the evolutionary origins of the brain. In a comparative eco-evo-devo approach, 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 amphioxus and sea anemone. 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 Campus, we plan to 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, involving early developmental as well as differentiation stages.
Finally, we are also interested in exploring population genetics and the variability of development and differentiation in different habitats and conditions. To this end, we are collecting strains of Platynereis and amphioxus as part of the Tara Oceans expedition.