The amphioxus SoxB family: implications for the evolution of vertebrate placodes.
The amphioxus SoxB family: implications for the evolution of vertebrate placodes.
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DOI：
10.7150/ijbs.3.356
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发表时间：
2007-08-06
影响因子：
9.2
通讯作者：
Bronner-Fraser M
中科院分区：
文献类型：
--
作者：
Meulemans D;Bronner-Fraser M
颅基板是增厚的外胚层区域，在脊椎动物头部产生感觉器官和神经节。在尾索动物中可能存在类似的结构，但在头索动物中没有发现，这表明最初的脊索动物缺乏板状体。SoxB基因在脊椎动物基板的离散子集中表达。为了研究脊椎动物中基板类的起源和多样性，我们从文昌鱼中分离了完整的SoxB基因，并分析了它们在胚胎和幼虫中的表达。我们发现，文昌鱼具有一个单一的SoxB2基因，它有三个SoxB1旁系同源。与脊椎动物SoxB1基因一样，这些旁系同源基因之一在非神经外胚层中表达，注定会产生感觉细胞。当考虑在其他文昌鱼基板标记直系同源物的情况下，文昌鱼SoxB1的表达表明，利用不同的基板型基因程序的感觉细胞类型的多样性存在于第一脊索动物。我们的数据支持基板的进化和多样化的模型，即脊椎动物基板的完整的补充，通过连续招聘不同的感觉细胞规格程序前基板外胚层。
Cranial placodes are regions of thickened ectoderm that give rise to sense organs and ganglia in the vertebrate head. Homologous structures are proposed to exist in urochordates, but have not been found in cephalochordates, suggesting the first chordates lacked placodes. SoxB genes are expressed in discrete subsets of vertebrate placodes. To investigate how placodes arose and diversified in the vertebrate lineage we isolated the complete set of SoxB genes from amphioxus and analyzed their expression in embryos and larvae. We find that while amphioxus possesses a single SoxB2 gene, it has three SoxB1 paralogs. Like vertebrate SoxB1 genes, one of these paralogs is expressed in non-neural ectoderm destined to give rise to sensory cells. When considered in the context of other amphioxus placode marker orthologs, amphioxus SoxB1 expression suggests a diversity of sensory cell types utilizing distinct placode-type gene programs was present in the first chordates. Our data supports a model for placode evolution and diversification whereby the full complement of vertebrate placodes evolved by serial recruitment of distinct sensory cell specification programs to anterior pre-placodal ectoderm.