![]() To study dendrite maturation of mitral cells, the transgenic (Tg) mouse pThy1-YFP 21 was used to selectively visualize mitral cells in which the Thy1 promoter specifically induces expression of yellow fluorescent protein (YFP). In order to address what mediates the matching with glomeruli, we analyze partner finding and dendrite selection of mitral cells in various mutant mice with deficits in glomerular map formation.ĭendrite selection and odorant receptor identities of glomeruli ![]() If this is the case, it is important for mitral cells to migrate to proper locations in the olfactory bulb to make the circuit functional 19. Mitral-cell dendrites may find their partner OSN axons based on their proximity to the target glomeruli without regard to odorant-receptor specificity. Is there any molecular code expressed in the mitral-cell dendrites for finding their partner glomeruli? Another possibility is that there is no such a molecular code of mitral cells to be recognized by OSN axons for proper matching to trigger the synapse formation. This then engenders the question of the identity of mitral cells and how it is recognized by OSN axons. If this is the case, the identity of OSNs is likely established by the expressed odorant receptor species. One possibility is that OSN axons and mitral-cell dendrites recognize the partners’ identity when the matching is taking place. The question to be answered is how both parties are able to find the right counterparts. Here, we study matching between the OSN axons and mitral-cell dendrites in the mouse olfactory system. Then, how are mouse M/T cells able to find their partner glomeruli for synapse formation? Even in mice, however, proper matching and connections are required to induce innate odor responses 18, 19, 20. ![]() In contrast, in the mouse olfactory system, much of targeting occurs autonomously by axon–axon interactions of OSNs without involving target cues 14, 15, 16, 17. This genetically-programmed pre-specification of ORNs generates hard-wired circuits that induce stereotyped innate odor responses. In the olfactory systems of the fly and nematode, projection neurons are pre-specified by the cell lineage and birth order to form synapses with incoming axons of olfactory receptor neurons (ORNs) 10, 11, 12, 13. In the mouse olfactory bulb, the odorous information is further processed by local neuronal circuits and conveyed by mitral/tufted (M/T) cells to the olfactory cortex 9. In mice, odorous information detected in the olfactory epithelium is converted to a two-dimensional map of activated glomeruli in the olfactory bulb, enabling the brain to discriminate a variety of odorants 8. Thus, each glomerulus represents one odorant receptor species in the olfactory bulb 5, 6, 7. Furthermore, OSNs expressing the same odorant receptor species converge their axons to a specific site to form a glomerular structure. Olfactory sensory neurons (OSNs) in the olfactory epithelium stochastically express only one functional odorant receptor gene in a monoallelic manner 2, 3, 4. In the mouse olfactory system, various odorants are detected using a repertoire of approximately 1000 odorant receptors 1.
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