Meeting Abstract
97.4 Thursday, Jan. 7 On the Origin and Evolution of Animal Vision: Insights from an Eyeless Cnidarian. PLACHETZKI, D/P*; FONG, C/R; OAKLEY, T/H; University of California, Davis; University of California, Santa Barbara; University of California, Santa Barbara plachetzki@ucdavis.edu
Opsin-based phototransduction underlies all known visual phenotypes in animals. In bilaterians these protein cascades translate light information into changes in either cyclic nucleotide gated (CNG) or transient receptor potential (TRP) ion channel activity. Cnidarians are the earliest branching animal lineage to possess opsin-based photosensitivity but little is known about the ion channel component of the cnidarian system or its function. Such data are vital if we are to understand the evolution of phototransduction and the apparent dichotomy that exists in bilaterians. Here we combine studies of comparative genomics, gene expression and behavioral pharmicogenetics to show that a CNG-based photosystem functions in the hydrozoan Hydra magnipapillata. Opsin, CNG and other phototransduction genes are specifically co-expressed in hydra sensory neurons and battery complex cells. Both contraction responsiveness and nematocyte discharge are modulated by ambient light intensity and the former is perturbed by the CNG inhibitor cis-diltiazem. We combine our results with previous data on phototransduction cascade composition from a broad sample of animal taxa to show that that the ancestral pathway –that which gave rise to all present modes of animal vision- also utilized a CNG ion channel in phototransduction. Our results contrast the deep evolutionary history of CNG-based phototransduction, today used in the visual systems of various animal lineages including vertebrates, with the more recent evolutionary origin of TRP-based systems that are common to the visual systems of modern invertebrates. Our results also add a new dimension to our understanding of the sensory biology of the nematocyte, a cellular lineage already known to express both chemosensitivity and mechanosensitivity.
