Moret Frédéric, Christiaen Lionel, Deyts Carole, Blin Maryline, Joly Jean-Stéphane, Vernier Philippe
Development, Evolution, Plasticity of the Nervous System, UPR 2197, Institut de Neurobiologie Alfred Fessard, C.N.R.S., 1, ave de la Terrasse, F-91198 Gif-sur-Yvette, France.
Eur J Neurosci. 2005 Jun;21(11):3043-55. doi: 10.1111/j.1460-9568.2005.04147.x.
Dopamine is a major neuromodulator synthesized by numerous cell populations in the vertebrate forebrain and midbrain. Owing to the simple organization of its larval nervous system, ascidian tunicates provide a useful model to investigate the anatomy, neurogenesis and differentiation of the dopaminergic neural network underlying the stereotypical swimming behaviour of its chordate-type larva. This study provides a high-resolution cellular analysis of tyrosine hydroxylase (TH)-positive and dopamine-positive cells in Ciona intestinalis embryos and larvae. Dopamine cells are present only in the sensory vesicle of the Ciona larval brain, which may be an ancestral chordate feature. The dopamine-positive cells of the ascidian sensory vesicle are located in the expression domain of homologues of vertebrate hypothalamic markers. We show here that the larval coronet cells also arise from this domain. As a similar association between coronet cells and the hypothalamus was reported in bony and cartilaginous fishes, we propose that part of the ascidian ventral sensory vesicle is the remnant of a proto-hypothalamus that may have been present in the chordate ancestor. As dopaminergic cells are specified in the hypothalamus in all vertebrates, we suggest that the mechanisms of dopamine cell specification are conserved in the hypothalamus of Ciona and vertebrates. To test this hypothesis, we have identified new candidate regulators of dopaminergic specification in Ciona based on their expression patterns, which can now be compared with those in vertebrates.
多巴胺是一种主要的神经调质，由脊椎动物前脑和中脑的众多细胞群体合成。由于海鞘幼虫神经系统结构简单，它为研究其脊索动物型幼虫刻板游泳行为背后多巴胺能神经网络的解剖结构、神经发生和分化提供了一个有用的模型。本研究对玻璃海鞘胚胎和幼虫中的酪氨酸羟化酶（TH）阳性细胞和多巴胺阳性细胞进行了高分辨率的细胞分析。多巴胺能细胞仅存在于玻璃海鞘幼虫脑的感觉泡中，这可能是脊索动物的一个祖先特征。海鞘感觉泡中的多巴胺阳性细胞位于脊椎动物下丘脑标志物同源物的表达域中。我们在此表明，幼虫的冠状细胞也起源于该区域。由于在硬骨鱼和软骨鱼中也报道了冠状细胞与下丘脑之间存在类似的关联，我们提出海鞘腹侧感觉泡的一部分是原始下丘脑的残余，而原始下丘脑可能存在于脊索动物祖先中。由于多巴胺能细胞在所有脊椎动物的下丘脑中都有特定的分布，我们认为多巴胺能细胞特定分布的机制在玻璃海鞘和脊椎动物的下丘脑中是保守的。为了验证这一假设，我们根据其表达模式在玻璃海鞘中鉴定了多巴胺能特定分布的新候选调节因子，现在可以将其与脊椎动物中的调节因子进行比较。
