Abstract
Neurons typically remodel axons/dendrites for functional refinement of neural circuits in the developing brain. Mitral cells in the mammalian olfactory system remodel their dendritic arbors in the perinatal development, but the underlying molecular and cellular mechanisms remain elusive in part due to a lack of convenient methods to label mitral cells with single-cell resolution. Here we report a novel method for single-cell labeling of mouse mitral cells using adeno-associated virus (AAV)-mediated gene delivery. We first demonstrated that AAV injection into the olfactory ventricle of embryonic day 14.5 (E14.5) mice preferentially labels mitral cells in the olfactory bulb (OB). Birthdate labeling indicated that AAV can transduce mitral cells independently of their birthdates. Furthermore, in combination with the Cre-mediated gene expression system, AAV injection allows visualization of mitral cells at single-cell resolution. Using this AAV-mediated single-cell labeling method, we investigated dendrite development of mitral cells and found that ~50% of mitral cells exhibited mature apical dendrites with a single thick and tufted branch before birth, suggesting that a certain population of mitral cells completes dendrite remodeling during embryonic stages. We also found an atypical subtype of mitral cells that have multiple dendritic shafts innervating the same glomeruli. Our data thus demonstrate that the AAV-mediated labeling method that we reported here provides an efficient way to visualize mitral cells with single-cell resolution and could be utilized to study dynamic aspects as well as functions of mitral cells in the olfactory circuits.
Highlights
Mammalian olfactory sensory neurons relay odor information to the olfactory bulb (OB), where olfactory sensory axons form synapses with dendrites of mitral cells and tufted cells, the second-order projection neurons in the OB (Malun and Brunjes, 1996; Blanchart et al, 2006)
We developed an associated virus (AAV)-mediated labeling system for mouse mitral cells in a single cell resolution
We first demonstrated that AAV injection into the olfactory ventricle at E14.5 leads to preferential gene transduction to mitral cells (Figure 1)
Summary
Mammalian olfactory sensory neurons relay odor information to the olfactory bulb (OB), where olfactory sensory axons form synapses with dendrites of mitral cells and tufted cells, the second-order projection neurons in the OB (Malun and Brunjes, 1996; Blanchart et al, 2006). Mitral cell dendrites undergo extensive remodeling: mitral cells initially extend multiple dendritic branches to multiple glomeruli and subsequently lose all but one dendritic branch to maintain contact with a single glomerulus as they mature (Lin et al, 2000; Inoue et al, 2018). This dendrite remodeling is thought to require neural activity (Wong and Ghosh, 2002) and Notch activity (Muroyama et al, 2016) in mitral cells, but mechanisms underlying the dendrite remodeling in mitral cells are still incompletely understood
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