Sorting of axons according to their target destination is essential for axonal guidance in the developing nervous system. Intercellular interactions have been shown in virtually all experimental models to be critical in axon guidance, but a full understanding requires knowing the cellular and molecular underpinnings not only of neuron-neuron interactions but also of glia-neuron interactions. This proposal focuses on reciprocal glia-neuron interactions underlying the sorting of olfactory axons during development of the olfactory pathway, especially on the role of glial cells in regulating specific signaling pathways. During development, the axons of olfactory receptor neurons (ORNs) must shed the axonal associations they established in the periphery and form new odor response-specific relationships. In the moth Manduca sexta, ORN axons sort in a discrete, highly accessible, glia-rich region of the nerve that extends from the sensory epithelium to the brain. Development is initiated by ORN axons;later arriving axons abruptly change their growth pattern and their associations as soon as they enter this """"""""sorting zone"""""""". Importantly, the axons must interact with the glial cells to sort properly into fascicles destined for glomeruli in the olfactory lobe. Thus the sorting zone of Manduca is an especially advantageous preparation to ask questions about glia-axon signaling mechanisms underlying axon sorting and fasciculation. The studies use parallel in vivo and in vitro approaches to test the hypothesis that glial cells regulate the balance of specific positive (e.g., growth-promoting or adhesive) and negative (e.g., growth-inhibiting or repulsive) cues that guides sorting of ORN axons. EM, confocal and live- cell microscopy will be used to assay the contributions of the cell adhesion molecules Fasciclin II and Neuroglian, the receptor tyrosine kinases EGFR and FGFR, and the EphR/ephrin signaling system to axonal sorting. Manduca's olfactory system has sufficient complexity and similarity to the mammalian system to be a useful model in which to study sorting. Relevance : The long term goal is to elucidate the mechanisms of glia-neuron interactions that are likely to be common to olfactory development and development of many other CNS pathways. Understanding these reciprocal neuron-glia interactions will contribute to the foundation needed to conquer devastating developmental abnormalities of the nervous system and inadequate regenerative attempts following injury.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Research Project (R01)
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Somatosensory and Chemosensory Systems Study Section (SCS)
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Davis, Barry
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University of Arizona
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United States
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Gibson, Nicholas J; Tolbert, Leslie P; Oland, Lynne A (2012) Activation of glial FGFRs is essential in glial migration, proliferation, and survival and in glia-neuron signaling during olfactory system development. PLoS One 7:e33828
Gibson, Nicholas J (2011) Cell adhesion molecules in context: CAM function depends on the neighborhood. Cell Adh Migr 5:48-51
Mallory, Heather S; Gibson, Nicholas J; Hayashi, Jon H et al. (2011) Direct and glia-mediated effects of GABA on development of central olfactory neurons. Neuron Glia Biol 7:143-61
Oland, Lynne A; Gibson, Nicholas J; Tolbert, Leslie P (2010) Localization of a GABA transporter to glial cells in the developing and adult olfactory pathway of the moth Manduca sexta. J Comp Neurol 518:815-38
Gibson, Nicholas J; Tolbert, Leslie P; Oland, Lynne A (2009) Roles of specific membrane lipid domains in EGF receptor activation and cell adhesion molecule stabilization in a developing olfactory system. PLoS One 4:e7222