Date of Award

8-2006

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Sara Lindsay

Second Committee Member

Larry Mayer

Third Committee Member

Robert Gundersen

Abstract

The feeding behavior of benthic animals greatly influences the bioturbation of sediments, in turn affecting the physical and chemical properties of the sediment. Spionid polychaetes are one type of marine worm that use a pair of feeding palps (ciliated appendages) to collect sediment deposited on the benthos or in the water column. Chemoreception, or the "sense of smell", in many organisms including spionids influences their feeding behavior. Invertebrates detect chemicals through G protein coupled receptors, which then send messages through guanine nucleotide binding proteins (G proteins). These heterotrimeric G proteins are made of three subunits α, β, and γ. Chemosensory signaling in marine invertebrates is through three possible G proteins Gαq, Gαs, and Gαo/i. This study investigates the signal transduction of chemoreception through G proteins in Dipolydora quadrilobata, a spionid polychaete. Polymerase chain reaction and degenerate primers were used to clone several G protein subunits including Gβ, Gαq, Gαs,and Gαo/i from palp tissue cDNA. The localization of two putative chemosensory G proteins Gαq and Gαs, were determined at the tissue and ultrastructural levels. A confocal scanning laser microscope was used to visualize G proteins labeled by fluorescent antibodies in whole worms. A transmission electron microscope was used to visualize G proteins labeled by 10nm gold particles in ultrathin sections of feeding palps. We successfully cloned the partial sequences of Gβ, Gαq, Gαs, and Gαo/i. All four G protein subunits exhibited high sequence conservation compared to their respective protein sequences from other invertebrates and even humans. Any major functional and structural domains included within the partial sequences showed high identity compared to other invertebrate sequences implying a conservation of possible chemosensory function by the G protein. Localization of Gαq at the tissue level was visualized in feeding palps, nuchal organs, and tips of parapodia. The nuchal organs and some cilia on feeding palps are presumed to have chemosensory function. At the ultrastructural level, feeding palps revealed significant localization of gold particles (Gαq) to food groove cilia, laterallabfrontal cilia, and gland cells. Laterallabfrontal cilia are presumed to be chemosensory. Localization of G, revealed non-specific labeling at both tissue and ultrastructural levels. Immunolocalization of Gaq to the aforementioned tissues and structures implies a probable role of G protein signal transduction in those areas. The putative chemosensory Gαq protein localized to areas with presumed chemosensory function therefore, we conclude that it is highly probable that D. quadrilobata transduces chemosensory signals through Gαq, similar to other marine invertebrates.

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