THE EXPRESSION OF TENASCIN-C ALONG THE LAMPREY OLFACTORY PATHWAY DURING EMBRYONIC-DEVELOPMENT AND FOLLOWING AXOTOMY-INDUCED REPLACEMENT OF THE OLFACTORY RECEPTOR NEURONS

Extracellular guidance molecules affect the pathway of growing axons b y both attractive and repulsive interactions. Tenascin-C, a glycoprote in of the extracellular matrix, is localized along developing axonal p athways where it may function by repulsion, restricting axons within s pecific boundaries. The lamprey olfactory pathway offers an advantageo us model for studying the role of extracellular matrix proteins in axo n guidance because the entire pathway is readily seen in horizontal se ctions and because lesioning the olfactory nerve will induce the syste m into a new phase of coordinated neurogenesis and axon outgrowth. Alt hough tenascin-C expression was absent during embryonic development, o lfactory nerve fascicles contained tenascin-C-immunoreactivity (IR) du ring the larval stage. During retrograde degeneration, the fascicles l ost tenascin-C-IR. Diffuse unfasciculated axonal processes extending f rom the olfactory epithelium did not express tenascin-C-IR; however, a cetylated tubulin and GAP-43-IR was present, indicating axonal outgrow th. When the newly extended axons of olfactory receptor neurons conver ged to form fascicles, tenascin-C-IR was evident within the fascicular boundaries. The absence of tenascin-C expression when axonal process were short and diffuse, and its return when axons coalesced within fas cicles, supports the view that tenascin-C functions as a boundary mole cule in the olfactory pathway. (C) 1998 Elsevier Science B.V. All righ ts reserved.