Evolution of neural crest and placodes: amphioxus as a model for the ancestral vertebrate?
Evolution of neural crest and placodes: amphioxus as a model for the ancestral vertebrate?
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DOI：
10.1046/j.1469-7580.2001.19910085.x
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发表时间：
2001-07-01
影响因子：
2.4
通讯作者：
Holland, ND
中科院分区：
文献类型：
--
作者：
Holland, LZ;Holland, ND
最近对原脊索动物（海鞘被囊动物和文文鱼）的研究揭示了脊椎动物头部两种特征的可能祖先：神经嵴和基板。神经嵴可能是从脊椎动物的原脊索动物祖先的神经板-表皮边界两侧的细胞进化而来的。文文鱼的神经嵴标记基因（BMP2/4、Pax3/7、Msx、Dll和Snail）的同源基因在神经板边缘和/或邻近的非神经外胚层表达。其中一些标记在被囊动物中也有类似的表达。然而，在原脊索动物中，这些细胞不像脊椎动物的神经嵴，既不能通过胚胎组织作为个体迁移，也不能分化成广泛的细胞类型。因此，虽然脊椎动物的原脊索动物祖先可能已经开始了神经嵴形成的遗传程序，但这一程序在最早的脊椎动物中得到了增强，以获得最终的神经嵴。在原脊索动物中缺乏脊椎动物基板的明确同源物。然而，文昌鱼和被囊动物都有外胚层感觉细胞。在被囊动物中，这些都是初级神经元，向中枢神经系统发送轴突，而在文文鱼中，外胚层感觉细胞包括初级神经元和缺乏轴突的次级神经元。发育基因表达的比较表明文昌鱼的前外胚层可能与脊椎动物嗅觉基板同源，嗅觉基板是脊椎动物中唯一具有初级而非次级神经元的基板。同样，生化、形态学和基因表达数据表明文昌鱼和被囊动物也具有腺垂体的同源物，腺垂体是少数脊椎动物结构之一，来源于非神经源性基板。相比之下，其他脊椎动物的基板的起源是非常不确定的。
Recent studies of protochordates (ascidian tunicates and amphioxus) have given insights into possible ancestors of 2 of the characteristic features of the vertebrate head: neural crest and placodes. The neural crest probably evolved from cells on either side of the neural plate-epidermis boundary in a protochordate ancestral to the vertebrates. In amphioxus, homologues of several vertebrate neural crest marker genes (BMP2/4, Pax3/7, Msx, Dll and Snail) are expressed at the edges of the neural plate and/or adjacent nonneural ectoderm. Some of these markers are also similarly expressed in tunicates. In protochordates, however, these cells, unlike vertebrate neural crest, neither migrate as individuals through embryonic tissues nor differentiate into a wide spectrum of cell types. Therefore, while the protochordate ancestor of the vertebrates probably had the beginnings of a genetic programme for neural crest formation, this programme was augmented in the earliest vertebrates to attain definitive neural crest. Clear homologues of vertebrate placodes are lacking in protochordates. However, both amphioxus and tunicates have ectodermal sensory cells. In tunicates these are all primary neurons, sending axons to the central nervous system, while in amphioxus, the ectodermal sensory cells include both primary neurons and secondary neurons lacking axons. Comparisons of developmental gene expression suggest that the anterior ectoderm in amphioxus may be homologous to the vertebrate olfactory placode, the only vertebrate placode with primary, not secondary, neurons. Similarly, biochemical, morphological and gene expression data suggest that amphioxus and tunicates also have homologues of the adenohypophysis, one of the few vertebrate structures derived from nonneurogenic placodes. In contrast, the origin of the other vertebrate placodes is very uncertain.