||Richi Sakaguchi, Marcus N. Leiwe, Takeshi Imai, Bright multicolor labeling of neuronal circuits with fluorescent proteins and chemical tags, ELIFE, 10.7554/eLife.40350, 7, 2018.11, The stochastic multicolor labeling method 'Brainbow' is a powerful strategy to label multiple neurons differentially with fluorescent proteins; however, the fluorescence levels provided by the original attempts to use this strategy were inadequate. In the present study, we developed a stochastic multicolor labeling method with enhanced expression levels that uses a tetracycline-operator system (Tetbow). We optimized Tetbow for either plasmid or virus vector-mediated multicolor labeling. When combined with tissue clearing, Tetbow was powerful enough to visualize the three-dimensional architecture of individual neurons. Using Tetbow, we were able to visualize the axonal projection patterns of individual mitral/tufted cells along several millimeters in the mouse olfactory system. We also developed a Tetbow system with chemical tags, in which genetically encoded chemical tags were labeled with synthetic fluorophores. This was useful in expanding the repertoire of the fluorescence labels and the applications of the Tetbow system. Together, these new tools facilitate light-microscopy-based neuronal tracing at both a large scale and a high resolution..
||Ryo Iwata, Hiroshi Kiyonari, Takeshi Imai, Mechanosensory-Based Phase Coding of Odor Identity in the Olfactory Bulb, Neuron, 10.1016/j.neuron.2017.11.008, 96, 5, 1139-1152.e7, 2017.12, Mitral and tufted (M/T) cells in the olfactory bulb produce rich temporal patterns of activity in response to different odors. However, it remains unknown how these temporal patterns are generated and how they are utilized in olfaction. Here we show that temporal patterning effectively discriminates between the two sensory modalities detected by olfactory sensory neurons (OSNs): odor and airflow-driven mechanical signals. Sniff-induced mechanosensation generates glomerulus-specific oscillatory activity in M/T cells, whose phase was invariant across airflow speed. In contrast, odor stimulation caused phase shifts (phase coding). We also found that odor-evoked phase shifts are concentration invariant and stable across multiple sniff cycles, contrary to the labile nature of rate coding. The loss of oscillatory mechanosensation impaired the precision and stability of phase coding, demonstrating its role in olfaction. We propose that phase, not rate, coding is a robust encoding strategy of odor identity and is ensured by airflow-induced mechanosensation in OSNs. Iwata et al. demonstrate that phase coding, but not rate coding, in mitral cells is useful for concentration-invariant odor identity coding. They also found that mechanosensation in olfactory sensory neurons facilitates, rather than masks, the robust phase coding of odors..