Interpreting amphioxus, and thoughts on ancestral chordate mouths and brains
Interpreting amphioxus, and thoughts on ancestral chordate mouths and brains
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DOI：
10.1387/ijdb.170105tl
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发表时间：
2017-01-01
影响因子：
0.7
通讯作者：
Lacalli, Thurston
中科院分区：
文献类型：
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作者：
Lacalli, Thurston
文昌鱼作为祖先脊索动物的模型越来越重要。然而，它是以各种方式进行二次修改，特别是在幼虫中，其小尺寸导致结构的重新缩放和重新定位。这在头部区域尤其明显，在那里嘴在左侧不对称地张开，导致推测嘴是次级衍生的，例如从鳃裂，因此与其他动物的嘴不同源。提交人认为，现有证据并不支持这一解释。第二个问题是提出有关的身份和功能的中脑同源物，其程度取决于是否更大的重量是给予背部的标志在神经索或腹侧的。两组背侧光感受器（板层体和约瑟夫细胞）的存在，在功能上将它们占据的区域与脊椎动物中脑联系起来。中脑目前被认为是在早期脊椎动物进化过程中出现初级意识的大脑区域，因此其组成细胞的起源特别有趣。可能的文昌鱼同源物包括最前组的背双极细胞（ADBs），其以与脊椎动物中的皮质神经元相同的方式顶端-基底倒置（即承载突触的神经突从顶端细胞隔室产生）。这可能是脊索动物的一项重要创新，脊索动物负责改善感觉处理，并最终改善意识。
Amphioxus is increasingly important as a model for ancestral chordates. Nevertheless, it is secondarily modified in various ways, especially in the larva, whose small size has resulted in a rescaling and repositioning of structures. This is especially pronounced in the head region, where the mouth opens asymmetrically on the left side, leading to speculation that the mouth is secondarily derived, e.g. from a gill slit, and is hence not homologous with mouths in other animals. The available evidence does not, in the author's view, support this interpretation. A second issue is raised concerning the identity and function of the midbrain homolog, whose extent depends on whether greater weight is given to dorsal landmarks in the nerve cord or ventral ones. The presence of two sets of dorsal photoreceptors, the lamellar body and Joseph cells, functionally links the region they occupy to the vertebrate midbrain. The midbrain is currently suggested to be the brain region in which primary consciousness emerged during early vertebrate evolution, so the origin of its constituent cells is of special interest. Possible amphioxus homologs include the anterior-most group of dorsal bipolar cells (ADBs), which are apico-basally inverted (i.e. synapse-bearing neurites arise from the apical cell compartment) in the same fashion as cortical neurons in vertebrates. This may have been a crucial innovation for chordates, responsible for both improved sensory processing and, eventually, consciousness.