Placodes and neural crests represent defining features of vertebrates, yet their relationship remains unclear despite extensive investigation1–3. Here we use a combination of lineage tracing, gene disruption and single-cell RNA-sequencing assays to explore the properties of the lateral plate ectoderm of the proto-vertebrate, Ciona intestinalis. There are notable parallels between the patterning of the lateral plate in Ciona and the compartmentalization of the neural plate ectoderm in vertebrates4. Both systems exhibit sequential patterns of Six1/2, Pax3/7 and Msxb expression that depend on a network of interlocking regulatory interactions4. In Ciona, this compartmentalization network produces distinct but related types of sensory cells that share similarities with derivatives of both cranial placodes and the neural crest in vertebrates. Simple genetic disruptions result in the conversion of one sensory cell type into another. We focused on bipolar tail neurons, because they arise from the tail regions of the lateral plate and possess properties of the dorsal root ganglia, a derivative of the neural crest in vertebrates5. Notably, bipolar tail neurons were readily transformed into palp sensory cells, a proto-placodal sensory cell type that arises from the anterior-most regions of the lateral plate in the Ciona tadpole6. Proof of transformation was confirmed by whole-embryo single-cell RNA-sequencing assays. These findings suggest that compartmentalization of the lateral plate ectoderm preceded the advent of vertebrates, and served as a common source for the evolution of both cranial placodes and neural crest3,4.Similarities between the patterning of the lateral plate in Ciona and of the neural plate ectoderm in vertebrates indicate that compartmentalization of the lateral plate ectoderm preceded the advent of vertebrates.

中文翻译：

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脊椎动物神经嵴和颅基板的共同进化起源

基板和神经嵴代表了脊椎动物的定义特征，尽管进行了广泛的调查1-3，但它们的关系仍不清楚。在这里，我们使用谱系追踪、基因破坏和单细胞 RNA 测序分析的组合来探索原始脊椎动物 Ciona 肠道侧板外胚层的特性。在 Ciona 中侧板的图案与脊椎动物中神经板外胚层的区室化之间存在显着的相似之处。两个系统都表现出依赖于互锁调节相互作用网络的 Six1/2、Pax3/7 和 Msxb 表达的序列模式。在 Ciona，这种划分网络产生不同但相关类型的感觉细胞，这些感觉细胞与脊椎动物的颅基板和神经嵴的衍生物有相似之处。简单的遗传破坏会导致一种感觉细胞类型转变为另一种感觉细胞类型。我们专注于双极尾神经元，因为它们来自侧板的尾部区域，并具有背根神经节的特性，背根神经节是脊椎动物神经嵴的衍生物5。值得注意的是，双极尾神经元很容易转化为触须感觉细胞，这是一种起源于 Ciona 蝌蚪侧板最前部区域的原基板感觉细胞类型。转化的证据通过全胚胎单细胞 RNA 测序分析得到证实。这些发现表明侧板外胚层的区室化早于脊椎动物的出现，并且是颅基板和神经嵴进化的共同来源3,4。