Horie Takeo, Kusakabe Takehiro, Tsuda Motoyuki
Department of Life Science, Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan.
J Comp Neurol. 2008 May 10;508(2):249-63. doi: 10.1002/cne.21678.
Glutamate is a major neurotransmitter in the excitatory synapses of both vertebrate and invertebrate nervous systems and is involved in many neural processes including photo-, mechano-, and chemosensations, neural development, motor control, learning, and memory. We identified and characterized the gene (Ci-VGLUT) encoding a member of the vesicular glutamate transporter subfamily, a specific marker of glutamatergic neurons, in the ascidian Ciona intestinalis. The Ci-VGLUT gene is expressed in the adhesive organ, the epidermal neurons, and the brain vesicle, but not in the visceral ganglion. The Ci-VGLUT promoter and an anti-Ci-VGLUT antibody were used to analyze the distribution and axonal connections of prospective glutamatergic neurons in the C. intestinalis larva. The green fluorescent protein (GFP) reporter driven by the 4.6-kb upstream region of Ci-VGLUT recapitulated the endogenous gene expression patterns and visualized both the cell bodies and neurites of glutamatergic neurons. Papillar neurons of the adhesive organs, almost all epidermal neurons, the otolith cell, and ocellus photoreceptor cells were shown to be glutamatergic. Each papillar neuron connects with a rostral epidermal neuron. Axons from rostral epidermal neurons, ocellus photoreceptor cells, and neurons underlying the otolith terminate in the posterior brain vesicle. Some caudal epidermal neurons also send long axons toward the brain vesicle. The posterior brain vesicle contains a group of Ci-VGLUT-positive neurons that send axons posteriorly to the visceral ganglion. Our results suggest that glutamatergic neurotransmission plays a major role in sensory systems and in the integration of the sensory inputs of the ascidian larva.
谷氨酸是脊椎动物和无脊椎动物神经系统兴奋性突触中的主要神经递质，参与许多神经过程，包括光、机械和化学感觉、神经发育、运动控制、学习和记忆。我们在海鞘肠鳃纲动物中鉴定并表征了编码囊泡谷氨酸转运体亚家族成员的基因（Ci-VGLUT），该亚家族是谷氨酸能神经元的特异性标志物。Ci-VGLUT基因在粘附器官、表皮神经元和脑泡中表达，但在内脏神经节中不表达。利用Ci-VGLUT启动子和抗Ci-VGLUT抗体分析了肠鳃纲动物幼虫中潜在谷氨酸能神经元的分布和轴突连接。由Ci-VGLUT上游4.6 kb区域驱动的绿色荧光蛋白（GFP）报告基因重现了内源性基因表达模式，并可视化了谷氨酸能神经元的细胞体和神经突。粘附器官的乳头神经元、几乎所有的表皮神经元、耳石细胞和眼点感光细胞均显示为谷氨酸能神经元。每个乳头神经元与一个吻侧表皮神经元相连。吻侧表皮神经元、眼点感光细胞和耳石下方神经元的轴突终止于后脑泡。一些尾侧表皮神经元也向后脑泡发出长轴突。后脑泡包含一组Ci-VGLUT阳性神经元，它们向后向内脏神经节发出轴突。我们的结果表明，谷氨酸能神经传递在海鞘幼虫的感觉系统和感觉输入整合中起主要作用。
