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 In Focus

Marine model organisms & functional genomics

Published 2000-01-15

In 2003 Professor Mike Thorndyke, Director and Chair of Experimental Marine Biology at Kristineberg Marine Research Station received a STINT Institutional Grant for cooperation with Dr Euan Brown, Stazione Zoologica in Naples, Italy. The annual grant of SEK 450 000 is intended for cooperation within Marine Model Organisms & Functional Genomics; Development, Regeneration and Cell Signalling

We are bringing together the expertise of two of the oldest and most prestigious marine laboratories in the world in a modern research programme designed to use simple marine model organisms to understand the complex process of regeneration. There is now much attention focussed on the “stem cell debate” because stem cells (undifferentiated cells that may grow to form any tissue including nerves) potentially are powerful clinical tools to help fight disease and traumatic injury in humans. However, one of the problems is that humans (and mammals in general) do not easily regenerate as adults. It is only embryonic “stem cells” that retain the “plastic” ability to generate any type of body tissue. Herein lies the problem, because there are serious ethical issues associated with studying and using embryonic tissues in the clinical environment.

In striking contrast with mammals, several simple marine animals show amazing powers of regeneration and tissue renewal as adults. In our project we are focussing on echinoderms (sea stars and brittlestars) as well as tunicates (sea squirts) as both of these groups of animals are closely related in evolution to vertebrates and share similar sets of genes but in a more simple arrangement.

The systems we are using include the solitary tunicate Ciona for which the complete genome (the sequences of all of its genes) is now available. This species can regenerate a complete replacement brain following loss of the original. We also use a colonial tunicate that produces buds from prexisting adults that grow into new and independent adults as well as brittlestars and seastars that, as adults, can regenerate complete arms. These simple animals are being compared to the octopus, an example of a supposedly more “primitive” and ancient group of animals, the molluscs. Octopus however have highly complex and sophisticated nervous system which, interestingly may not regenerate as effectively as the apparently more advanced, sea stars and tunicates.

In the first year of this project we have concentrated on two areas. First we have made “cDNA libraries” from octopus brain and brittlestar arms. In principle these libraries contain copies of all the genes operating or “switched on” in these tissues. We have begun to analyse the sequences of some of the genes and are able to compare the octopus and brittlestar genes with each other and with those available from gene data bases on mammals, fish, flies etc. This way we can identify the octopus and brittlestar counterparts that are likely to be important in nerve function, growth and regeneration. We have also begun to develop techniques for “in situ hybridization”. This is a method that allows us to identify the cells, in the tissues that are using these genes. We are doing this for Octopus, brittlestar and the adult tunicate Ciona intestinalis, for which the whole genome is already available.

In parallel we have also commenced a programme designed to analyse the functional recovery of starfish arms following nerve cord damage and their subsequent regeneration. It is well known that after section of a nerve in a starfish arm that the nerve grows back in around 25-35 days. But at what point does the nervous network recover its normal activity (coordination of arm movements for locomotion, feeding etc)? We developed a behavioural assay to test the ability of starfish to track their mussel prey before and after cutting the nerve cord in one arm. The results show that in the first week after the cut, the loss of control over one arm has little effect on motor performance. However during the following weeks, performance gets progressively worse until at around 30 days when it begins to improve again. At around 60 days after the cut, the animals apparently show normal behaviour. Our data indicate that after morphological degeneration of the nerve, synaptic degeneration and network disruption, there is period of regrowth, remodelling and refinement of motor programs. This study will help to refine the search for genes involved in these different steps of nerve regeneration by providing an outline of the time courses of these processes.

Mike Thorndyke, Kristineberg Marine Research Station

Euan Brown, Statione Zoologica Napoli

Senast uppdaterad: 06-10-05 21:29

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