The neural crest is an embryonic stem cell population unique to vertebrates¹ whose expansion and diversification are thought to have promoted vertebrate evolution by enabling emergence of new cell types and structures such as jaws and peripheral ganglia². Although jawless vertebrates have sensory ganglia, convention has it that trunk sympathetic chain ganglia arose only in jawed vertebrates^3,4,5,6,7,8. Here, by contrast, we report the presence of trunk sympathetic neurons in the sea lamprey, Petromyzon marinus, an extant jawless vertebrate. These neurons arise from sympathoblasts near the dorsal aorta that undergo noradrenergic specification through a transcriptional program homologous to that described in gnathostomes. Lamprey sympathoblasts populate the extracardiac space and extend along the length of the trunk in bilateral streams, expressing the catecholamine biosynthetic pathway enzymes tyrosine hydroxylase and dopamine β-hydroxylase. CM-DiI lineage tracing analysis further confirmed that these cells derive from the trunk neural crest. RNA sequencing of isolated ammocoete trunk sympathoblasts revealed gene profiles characteristic of sympathetic neuron function. Our findings challenge the prevailing dogma that posits that sympathetic ganglia are a gnathostome innovation, instead suggesting that a late-developing rudimentary sympathetic nervous system may have been characteristic of the earliest vertebrates.

神经嵴是脊椎动物特有的胚胎干细胞群¹，其扩张和多样化被认为通过出现新的细胞类型和结构（如颌和外周神经节）来促进脊椎动物的进化²。尽管无颌脊椎动物有感觉神经节，但传统上认为躯干交感链神经节仅出现在有颌脊椎动物中^3,4,5,6,7,8。相比之下，我们在这里报告了海七鳃鳗（ Petromyzon marinus ）（一种现存的无颌脊椎动物）中存在躯干交感神经元。这些神经元起源于背主动脉附近的交感母细胞，通过与颌口动物中描述的转录程序同源的转录程序进行去甲肾上腺素能规范。七鳃鳗交感神经细胞分布在心外空间，并沿双侧流的躯干长度延伸，表达儿茶酚胺生物合成途径酶酪氨酸羟化酶和多巴胺β-羟化酶。 CM-DiI谱系追踪分析进一步证实这些细胞来源于躯干神经嵴。对分离的ammocoete躯干交感母细胞的RNA测序揭示了交感神经元功能特征的基因谱。我们的研究结果挑战了普遍认为交感神经节是颚口类动物的创新的教条，相反表明晚期发育的基本交感神经系统可能是最早脊椎动物的特征。