Whitlock K E, Westerfield M
Section of Genetics and Development, Cornell University, Ithaca, New York 14853-2703, USA.
J Neurosci. 1998 Nov 1;18(21):8919-27. doi: 10.1523/JNEUROSCI.18-21-08919.1998.
Mechanisms guiding the first axons from the olfactory placode of the peripheral nervous system (PNS) to the olfactory bulb in the vertebrate CNS are unknown. We analyzed the initial outgrowth of axons from the olfactory placode in zebrafish and found a precocious transient class of pioneer neurons that prefigure the primary olfactory pathway before outgrowth of olfactory sensory axons or expression of olfactory receptor genes. Not only are the pioneers antigenically, morphologically, and spatially distinct from olfactory sensory neurons, they are also developmentally distinct; via fate mapping, we show that they arise from a more anterior region of the lateral neural plate than do the first sensory neurons. After the axons of the sensory neurons grow into the CNS, the pioneer neurons undergo apoptotic cell death. When we ablated the pioneers before axonogenesis, the following sensory axons showed severe misrouting. We propose that the pioneers provide the first necessary connection from the PNS to the CNS and that they establish an axonal scaffold for the later-arriving olfactory sensory neurons.
引导外周神经系统（PNS）嗅基板的首批轴突进入脊椎动物中枢神经系统（CNS）嗅球的机制尚不清楚。我们分析了斑马鱼嗅基板轴突的初始生长，发现了一类早熟的瞬时先驱神经元，它们在嗅觉感觉轴突生长或嗅觉受体基因表达之前就预先形成了主要嗅觉通路。这些先驱神经元不仅在抗原性、形态和空间上与嗅觉感觉神经元不同，在发育上也不同；通过命运图谱，我们发现它们比首批感觉神经元起源于外侧神经板更靠前的区域。当感觉神经元的轴突长入中枢神经系统后，先驱神经元会经历凋亡性细胞死亡。当我们在轴突发生之前消融先驱神经元时，随后的感觉轴突显示出严重的误路由。我们提出，先驱神经元提供了从外周神经系统到中枢神经系统的第一个必要连接，并为后来到达的嗅觉感觉神经元建立了一个轴突支架。
