Evolution of Potassium Channels and Nerve Networks in Cnidaria

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All animals have nervous systems - tissues formed of excitable cells that transmit and integrate information between different parts of the body. The structure and activity of nervous systems varies widely between organisms, from the relatively dispersed neural networks of the Cnidaria to the many anatomically different centralized nervous systems of the Bilateria. However, all cells of the nervous systems of all animals are electrically responsive. Ion channel proteins, both ligand-gated, which respond to neurotransmitters at the synapse and extra-synaptic modulatory signals, and voltage-gated, which respond to changes in membrane potential, modulate the membrane potential. This proposal describes a program aimed at identifying and characterizing the voltage-gated potassium channels in the cnidarian, Polyorchis penicillatus.***The natural process of evolution gives rise to a large number of homologs that differ in sequence but that have one common property - all the variants are functional in the context of the organisms in which they arise. We propose to isolate a total of 15 voltage-gated potassium channel cDNAs from P. penicillatus (in addition to the 6 that have been isolated to date). When the channels are cloned and sequenced we will express them individually in oocytes of Xenopus laevis to determine their electrophysiological properties, using the voltage clamp technique, and compare their sequences and activities to known channels from other organisms. These comparisons will allow us to formulate hypotheses about the relationship between the protein sequences and the activity of the channels, which we will test using a combination of synthetic mutagenesis and electrophysiological characterization. In parallel, we will prepare antibodies to each of these channels and map their locations in the adult medusa of the jellyfish, as a first step towards understanding the similarities and differences between the cnidarian nerve net and nervous systems from other organisms.***P. penicillatus has been a good choice for these studies. The adult form is a free-living medusa, unlike the other cnidarian model organisms, Hydra magnipapillata, a sessile polyp, and Nematostella vectensis, a sessile anemone. Thus, its nervous system has evolved to facilitate a motile rather than sessile life-style. It is large enough that electrophysiological studies on different components of its nervous system have proven straightforward. We have a thorough knowledge of the anatomy of the neural network in P. penicillatus. Six different voltage-gated potassium channels have already been isolated and electrophysiologically characterized. The results from those investigations have demonstrated the feasibility, power and validity of the overall approach that we are taking to this program.**