Sato Yuki, Miyasaka Nobuhiko, Yoshihara Yoshihiro
Laboratory for Neurobiology of Synapse, RIKEN Brain Science Institute, Saitama 351-0198, Japan.
J Neurosci. 2005 May 18;25(20):4889-97. doi: 10.1523/JNEUROSCI.0679-05.2005.
The olfactory epithelium of fish contains two major types of olfactory sensory neurons (OSNs) that are distinct morphologically (ciliated vs microvillous) and possibly functionally. Here, we found that these OSNs express different sets of signal transduction machineries: the ciliated OSNs express OR-type odorant receptors, cyclic nucleotide-gated channel A2 subunit, and olfactory marker protein (OMP), whereas the microvillous OSNs express V2R-type receptors and transient receptor potential channel C2 (TRPC2). To visualize patterns of axonal projection from the two types of OSNs to the olfactory bulb (OB), we generated transgenic zebrafish in which spectrally distinct fluorescent proteins are expressed in the ciliated and microvillous OSNs under the control of OMP and TRPC2 gene promoters, respectively. An observation of whole-mount OB in adult double-transgenic zebrafish revealed that the ciliated OSNs project axons mostly to the dorsal and medial regions of the OB, whereas the microvillous OSNs project axons to the lateral region of the OB. A careful histological examination of OB sections clarified that the axons from the two distinct types of OSNs target different glomeruli in a mutually exclusive manner. This segregation is already established at very early developmental stages in zebrafish embryos. These findings clearly demonstrate the relationships among cell morphology, molecular signatures, and axonal terminations of the two distinct types of OSNs and suggest that the two segregated neural pathways are responsible for coding and processing of different types of odor information in the zebrafish olfactory system.
鱼类的嗅觉上皮包含两种主要类型的嗅觉感觉神经元（OSN），它们在形态上（纤毛状与微绒毛状）不同，功能上可能也不同。在此，我们发现这些OSN表达不同的信号转导机制：纤毛状OSN表达OR型气味受体、环核苷酸门控通道A2亚基和嗅觉标记蛋白（OMP），而微绒毛状OSN表达V2R型受体和瞬时受体电位通道C2（TRPC2）。为了可视化这两种类型的OSN向嗅球（OB）的轴突投射模式，我们构建了转基因斑马鱼，其中在OMP和TRPC2基因启动子的控制下，分别在纤毛状和微绒毛状OSN中表达光谱不同的荧光蛋白。对成年双转基因斑马鱼的整装嗅球观察发现，纤毛状OSN的轴突大多投射到嗅球的背侧和内侧区域，而微绒毛状OSN的轴突投射到嗅球的外侧区域。对嗅球切片进行仔细的组织学检查表明，来自两种不同类型OSN的轴突以相互排斥的方式靶向不同的肾小球。这种分离在斑马鱼胚胎的非常早期发育阶段就已建立。这些发现清楚地证明了两种不同类型OSN的细胞形态、分子特征和轴突终末之间的关系，并表明这两条分离的神经通路负责斑马鱼嗅觉系统中不同类型气味信息的编码和处理。
