Meeting Abstract
Cnidarians such as the freshwater polyp Hydra magnipapillata display a surprisingly complex sensory repertoire capable of responding to light, chemical, and mechanical stimuli. The photo response in hydra is driven largely by an opsin-mediated phototransduction cascade that utilizes cyclic nucleotide gated ion channels, however, the intermediary enzymes involved in cnidarian phototransduction have not been directly examined. Previous work demonstrated an increase in cytosolic cAMP in heterologous gene expression studies of a jellyfish opsin. In eukaryotic cells, cAMP is generated by adenylate cyclase (AC) and a cross-reactive antibody against AC stained the photoreceptor layer of a cubozoan rhopalia. Here we directly test the possibility that AC acts in phototransduction in the hydra. We report an exhaustive phylogeny of metazoan AC genes and show that cnidarian genomes possess orthologs of metazoan AC9. Next we show riboprobes against hydra AC9 co-localize with opsin in a range of hydra sensory neurons. Finally, we use a simple photo response experiment, where dark-adapted hydra are presented with light of differencing wavelengths and assayed for contraction, in the presence and absence of drugs that effect AC activity. Our results suggest that AC activity is likely involved in the hydra photo response and may be a general feature of cnidarian phototransduction. We discuss these results in light of current hypotheses on the origin and diversification of animal phototransduction cascades.
