Ultrastructural Analyses on Chemosensory Signaling

Northwestern University, Evanston IL

Investigators

Abstract

Our overall goal is to understand the structural characteristics of cells of chemosensory organs, smell and taste, in relation to chemosensory functioning, and to inform about the impressive architecture of the subcellular structures where smell and taste recognition takes place. For olfactory (smell) systems this includes vomeronasal olfactory signaling, i.e., the signaling of a special olfactory organ particularly involved in conspecific and prey recognition. For a long time it was assumed that apical structures of the chemosensory receptor cells that line the nasal cavity, cilia and microvilli in olfactory and vomeronasal system, respectively, are the subcellular organelles specialized for capture and recognition of chemosensory stimuli. Thus it was assumed that these structures contain the main subcellular sites of chemosensory signal-transduction. However, firm proof for this was lacking. Cilia and microvilli are tentacle-shaped processes that sprout from receptor cell surfaces, but that have different internal cytoskeletal (=scaffolding) structures. Their elongated shape likely serves to increase the surface-to-volume ratio to enhance chances that odor molecules reach the receptor cells. We want to construct a graphical image of proteins important in the chemosensory signaling-cascades from the special membrane proteins thought to receive incoming odor molecules -- a family of proteins that resemble, e.g., the visual pigment rhodopsin -- to current generating ion channels, as well as of molecules involved in signal modulation and signal termination. For this we use a technique called immunocytochemistry that makes use of antibody markers which can, with appropriate tags, help to identify molecules of interest. In combination with ultrastructural methods using electron microscopy, immunocytochemistry is used to localize such molecular components in their exact subcellular position. With this approach we showed that the distal parts of the olfactory cilia contained most, if not all, components in the signal-onset cascades, from odor receptor to current-generating ion channel. We began similar studies on vomeronasal olfaction. The new project serves to continue research on the location of signal-onset molecules involved in vomeronasal olfaction, while in both main and vomeronasal olfactory systems molecules that are involved in other parts of the signaling cascades, modulation and termination, will be localized. Apart from the relevance to continued structural research in chemosensory signaling, my efforts are also important to advance and improve on ultrastructural methods for research in biology in general. While maintaining my research in a non-tenure track position I kept a small, but well equipped, electron microscope imaging facility alive at Northwestern University at minimal expense. Many such facilities have been closed, which is not good for biological research at large. During my stay at Northwestern several students participated in my projects. One such collaboration resulted in several publications. Perhaps, more important, I helped many colleagues and their students in their projects in case these projects required my special expertise in fine structural research. Whenever possible, I will continue such efforts during my stay at Northwestern. I also lectured widely at various schools, institutions and conferences, in the US as well as abroad, and organized seminars and special lectures, and hope to be able to continue such activities.