Abstract
In mammals, neural circuits are formed based on a genetic program and further refined by neuronal activity during the neonatal period. We report that in the mouse olfactory system, the glomerular map is not merely refined but newly connected to second-order neurons by odorant-receptor-derived neuronal activity. Here, we analyzed a pair of molecules, Sema7A, expressed in olfactory sensory neurons (OSNs) in an activity-dependent manner, and PlxnC1, localized to dendrites of mitral/tufted (M/T) cells in the first week after birth. In Sema7A or PlxnC1 knockout (KO) mice, initiation of synapse formation and dendrite selection of M/T cells were perturbed. Reconstitution and rescue experiments demonstrated that Sema7A–PlxnC1 interaction is essential to form the post-synaptic assembly. Pharmacological blocking experiments indicated that synaptic transmission triggers primary dendrite selection by synaptic competition. We conclude that Sema7A signaling is key to inducing activity-dependent post-synapse events and dendrite selection in M/T-cells during the neonatal period.
Highlights
The mouse olfactory system detects a variety of odorants using a repertoire of ~1000 odorant receptors (ORs)[1]
What mediates the synapse formation between olfactory sensory neurons (OSNs) axons and M/T-cell dendrites? How do they find their partners for proper synapse formation? What are the synaptic events involved in these processes? In an effort to address these questions, we searched for a pair of ligand and receptor molecules that are involved in synapse formation and dendrite selection of M/T cells
To determine what kinds of molecules are essential for initiating the synapse formation in glomeruli, we searched for a receptor and ligand pair each of which was expressed by OSN axons or M/T-cell dendrites
Summary
The mouse olfactory system detects a variety of odorants using a repertoire of ~1000 odorant receptors (ORs)[1]. After OSN axons reach their approximate destinations in the OB, further refinement of an olfactory map occurs through fasciculation of OSN axons in an activity-dependent manner[9]. Most of these processes take place by axon–axon interactions of OSNs10, proper connections are needed between OSN axons and the dendrites of M/T cells. What mediates the synapse formation between OSN axons and M/T-cell dendrites? In an effort to address these questions, we searched for a pair of ligand and receptor molecules that are involved in synapse formation and dendrite selection of M/T cells
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