| Research Abstract |
A transgenic approach has been quite useful for the studies in the olfactory system.
Recently, we reported the successful expression of a murine odorant receptor transgene, MOR28, tagged with a tau-lacZ fragment containing the internal ribosome entry site (IRES) (Nat. Neurosci. 3, 687-693, 2000). In our transgenic mouse, the endogenous gene was differently tagged with another reporter gene, IRES-gap-GFP, so that the expression of the two types of MOR28 genes can be detected separately. Double staining of the olfactory epithelium revealed that both transgenic and endogenous MOR28 genes are expressed in the same expected zone (zone 4), although they are activated in a mutually exclusive manner in individual olfactory sensory neurons (OSNs). As for the axonal projection, OSNs expressing the transgenic MOR28 (lacZ positive) were found to target to glomeruli adjacent to, but distinct from, those for the endogenous MOR28 gene (GFP positive), probably due to the differences in the nature of tagging and genetic polymorphism (Genes Cells 6, 71, 2001).
Furthermore, we found that the axon terminals of the two sets of MOR28-positive OSNs, one expressing the lacZ tag and the other expressing the GFP gene, are dispersed and intermingled at early developmental or regeneration stages (NeuroReport 12, 1061, 2001).Projection areas become more distinct and separated at later stages, however, two sets of axon fibers are not typically bundled or segregated during path finding, indicating that segregation of axons mainly occurs when they target at the olfactory bulb to form the glomerular structure.
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