TSIE, M*; LINDSAY, S; University of Maine, Orono: Immuno-localization of a putative chemosensory G-protein alpha-subunit in a spionid polychaete

Chemoreception controls feeding behavior in many animals. In most organisms, binding of external cues to odorant receptors activates guanine nucleotide binding proteins (G proteins), initiating signal transduction cascades that result in a behavioral response. G proteins are heterotrimers composed of &alpha, &beta, and &gamma subunits. Specifically, G_q proteins belong to one of several families capable of mediating signal transduction in chemoreception, but their role in polychaete chemoreception has not been described. The &alpha subunit is believed to be specific for a chemoreceptor and its corresponding G protein. The goal of this project was to investigate where G_q proteins are localized in a spionid polychaete, which could indicate where in the organism signal transduction of chemoreception is taking place. We used an antibody specific to the &alpha subunit of the G_q family in immunohistochemical assays to visualize localization at both the tissue and ultrastructural levels in the spionid polychaete, Dipolydora quadrilobata. Transmission electron microscopy detection of a colloidal gold-conjugated secondary antibody revealed localization of G_q in cilia of the palp food groove. In addition, confocal laser scanning microscopy along with fluorescent secondary antibodies revealed G_q localization in the palps, prostomium, nuchal organs, and parapodia. Our results show particularly strong immunoreactivity in the tips of the palps and the nuchal organs. Spionid polychaetes use their palps for feeding, and these results support previous studies suggesting that some ciliated cells on the palps are chemosensory. The observed immunoreactivity for the sensory G_q protein in the nuchal organs was expected, given that these are sensory structures, but whether the G-protein is specific to chemoreception signal transduction remains to be determined.