Neurobiology of marine zooplankton

Group Leader: Dr. Gáspár Jékely

Phone: +49 7071 601 1310

Group members: Alphabetical list

The brain of bilaterally symmetrical animals (Bilateria) evolved and diversified in a marine environment during the 'Cambrian explosion', one of the most spectacular events in the history of life. In order to gain insights into early events of brain evolution we study the nervous system of a marine polychaete, Platynereis dumerilii, a laboratory molecular model species of neurobiology and evo-devo. The planktonic larvae of Platynereis have a simple nervous system that can be studied molecularly and functionally at a cellular resolution. The larvae show behavioural responses such as phototaxis and gravitaxis that are regulated by simple sensory-motor neuronal networks. Our research aims at understanding the molecular, morphological and functional architecture of sensory-motor networks in the larval nervous system of Platynereis. We can manipulate these networks using pharmacology, laser nanosurgery and gene interference techniques. With the dissection of larval neuronal networks we expect to gain insights into the neurobiology of zooplankton migration and into the early evolution of animal brains.

Platynereis neurobiology

Platynereis emerged as a molecular model of comparative evo-devo and neurobiology. Molecular characterisation of neural patterning and cell types in the larval nervous system of Platynereis revealed remarkable molecular similarities to the vertebrate central nervous system. In essence, the Platynereis larval nervous system contains several conserved neuron types in an ancestral and simple arrangement. These features make it an ideal reference system to understand how the ancestral bilaterian brain looked like and how it diversified during animal evolution. Importantly, several of the brain-specific molecules in Platynereis (neuropeptides, transcription factors, G-protein coupled receptors) and the associated cell types, shared by vertebrates, are missing from the conventional terrestrial invertebrate model organisms due to secondary loss. Neurobiological studies in Platynereis have therefore enormous potential in comparative and evolutionary neuroscience. Platynereis is also an excellent model for experimental neurobiology and zooplankton migration. The combination of comparative evo-devo with experimental neuroscience and zooplankton biology opens up the exciting perspective of understanding the evolutionary history of individual neuron types, the way they build a nervous system, and the function of that nervous system in a marine environment.

Adult Platynereis dumerilii, a lithography of Friedrich Hempelmann from 1911.

Zooplankton migration

The migration of zooplankton is the largest biomass transport on Earth. In the first week of their life Platynereis larvae swim in the ocean as part of the zooplankton. The larval nervous system, consisting of about 100 neurons, has to interpret environmental cues and regulate the navigation of larvae in the open water until settlement on a suitable substrate. These tasks are probably very similar to the ones the first brains had to cope with during the rise of animals about 600 million years ago. However, despite its evolutionary and ecological significance, little is known about how the nervous system of planktonic larvae functions. A highly important aspect of Platynereis neurobiology is therefore to work out the molecular and functional architecture of the larval nervous system and to understand how it regulates the navigation of planktonic larvae.

2) Early axonal scaffold of a developing Platynereis larva. The larvae already swim and are phototactic at this stage.	3) Scanning electron micrograph of a Platynereis larva (by Harald Hausen, Freie Universität Berlin). The larvae swim with the equatorial belt of cilia.

Research goals

We would like to establish Platynereis as a model of behavioural neuroscience. To this end we are developing novel instrumentations and behavioural paradigms to study the behaviour of Platynereis larvae under controlled conditions. Using these tools in combination with pharmacological, nanosurgical and genetic manipulation techniques we would like to uncover the neurobiological and mechanical basis of zooplankton migration. We work in collaboration with optical engineers and physicists to develop precise detection and stimulation devices. We also use computer simulations of larval swimming to better characterise the system properties of behaviour.

4) One of the several sophisticated sensory cells in the Platynereis larval brain that read out changes in the marine environment.	5) Visualisation of cilia-generated water currents to study the beating of cilia.

Computer simulation of larval phototaxis (in collaboration with François Nédélec, EMBL).

Selected publications:

Conzelmann M, Offenburger SL, Asadulina S, Keller T, Münch TA, Jékely G. Neuropeptides regulate swimming depth of Platynereis larvae. 

PNAS, 2011 Oct 17. [Epub ahead of print]

Jékely G, Colombelli J, Hausen H, Guy K, Stelzer E, Nédélec F, Arendt D. Mechanism of phototaxis in marine zooplankton.

Nature, 2008; 456:395-9

Denes A ¹ Jékely G¹, Steinmetz P, Raible F, Snyman H, Prud’homme B, Ferrier D, Balavoine G, Arendt D. Molecular architecture of annelid nerve cord supports common origin of nervous system centralization in bilateria.

Cell, 2007; 129:277-288. ¹Equally contributing authors

Jékely G, Arendt D. Cellular resolution expression profiling using confocal detection of NBT-BCIP precipitate by reflection microscopy.

BioTechniques, 2007; 42: 751-755.

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