EXPRESSION OF GALECTIN-1 IN THE MOUSE OLFACTORY SYSTEM

Primary sensory olfactory axons arise from the olfactory neuroepitheli um that lines the nasal cavity and then project via the olfactory nerv e into the olfactory bulb. The P-galactoside binding lectin, galectin- 1,and its laminin ligand have been implicated in the growth of these a xons along this pathway. In galectin-1 null mutant mice, a subpopulati on of primary sensory olfactory axons fails to reach its targets in th e olfactory bulb. In the present study we examined the spatiotemporal expression pattern of galectin-1 in normal mice in order to understand its role in the development of the olfactory nerve pathway. At E15.5, when olfactory axons have already contacted the olfactory bulb, galec tin-1 was expressed in the cartilage and mesenchyme surrounding the na sal cavity but was absent from the olfactory neuroepithelium, nerve an d bulb. Between E16.5 and birth galectin-1 began to be expressed by ol factory nerve ensheathing cells in the lamina propria of the neuroepit helium and nerve fibre layer. Galectin-1 was neither expressed by prim ary sensory neurons in the olfactory neuroepithelium nor by their axon s in the olfactory nerve. Laminin, a galectin-1 ligand, also exhibited a similar expression pattern in the embryonic olfactory nerve pathway . Our results reveal that galectin-1 is dynamically expressed by glial elements within the nerve fibre layer during a discrete period in the developing olfactory nerve pathway. Previous studies have reported ga lectin-1 acts as a substrate adhesion molecule by cross-linking primar y sensory olfactory neurons to laminin. Thus, the coordinate expressio n of galectin-1 and laminin in the embryonic nerve fibre layer suggest s that these molecules support the adhesion and fasciculation of axons en route to their glomerular targets.