"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."
Animal vision was traditionally thought to be comprised of two distinct lineages of sensory cells that evolved separately in vertebrates vs. invertebrates. These photoreceptors differ fundamentally in the light sensor structure and the biochemistry to convert captured photons into electrical signals. Such view was challenged by the discovery of additional light-detection schemes and by clues pointing to a likely common origin for all photoreceptors. One pivotal finding was the identification of novel light-sensitive mammalian cells, which regulate the biological clock via a photon-capturing molecule, melanopsin, akin to those of invertebrates. However, the enormous divergence between these groups of animals makes comparative analysis arduous, exacerbated by the difficulties to characterize melanopsin-signaling in mammalian cells, owing to their scarcity. This impasse could be alleviated by examining some precursor of modern vertebrates, to bridge this evolutionary chasm. Amphioxus offers unique advantages, because genomic research established that it is the most basal living chordate and has remained close to its ancestral condition. It thus provides a favorable window to examine biological mechanisms as they may have existed when the vertebrate branch separated. Melanopsin has been detected in some identifiable amphioxus cells, but no functional study had been conducted; the investigators will capitalize on their initial results, demonstrating the feasibility to isolate these cells and measure light-induced electrical responses. The project will recruit and train graduate students at the Marine Biological Laboratory in Woods Hole. The Marine Biological Laboratory provides an outstanding environment for this work. A multi-pronged approach will characterize the photoresponse mechanisms, identify intermediate steps of stimulus-response coupling, and initiate their molecular characterization. The benefits will be two-fold: help clarify the evolution of light-sensing, and elucidate melanopsin signaling mechanisms, which remain largely elusive. The multi-disciplinary nature of the project provides a fertile ground to train young investigators, exposing them to issues ranging from evolutionary biology to sensory physiology and cellular biophysics; the technical arsenal will be correspondingly diverse, encompassing electrical and optical recording, molecular and immunological identification, and bio-informatics tools.