Despite their pivotal role, the evolutionary origins of vertebrate digestive systems remain enigmatic. We explored the cellular characteristics of the amphioxus ( Branchiostoma floridae ) digestive tract, a model for the presumed primitive chordate digestive system, using bulk tissue companioned with single-cell RNA sequencing. Our findings reveal segmentation and a rich diversity of cell clusters, and we highlight the presence of epithelial-like, ciliated cells in the amphioxus midgut and describe three types of endocrine-like cells that secrete insulin-like, glucagon-like, and somatostatin-like peptides. Furthermore, Pdx , Ilp1 , Ilp2 , and Ilpr knockout amphioxus lines revealed that, in amphioxus, Pdx does not influence Ilp expression. We also unravel similarity between amphioxus Ilp1 and vertebrate insulin-like growth factor 1 (Igf1) in terms of predicted structure, effects on body growth and amino acid metabolism, and interactions with Igf-binding proteins. These findings indicate that the evolutionary alterations involving the regulatory influence of Pdx over insulin gene expression could have been instrumental in the development of the vertebrate digestive system.

中文翻译：

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两栖动物消化道的单细胞分析揭示了脊索动物中内分泌细胞的保守性


尽管脊椎动物消化系统发挥着关键作用，但它们的进化起源仍然是个谜。我们探索了两栖动物 （ Branchiostoma floridae ） 消化道的细胞特征，这是一种假定的原始脊索动物消化系统的模型，使用大块组织与单细胞 RNA 测序相伴。我们的研究结果揭示了细胞簇的分割和丰富的多样性，我们强调了两栖中肠中存在上皮样纤毛细胞，并描述了三种分泌胰岛素样、胰高血糖素样和生长抑素样肽的内分泌样细胞。此外，Pdx 、 Ilp1 、 Ilp2 和 Ilpr 敲除两栖细胞系表明，在两栖动物中，Pdx 不影响 Ilp 表达。我们还揭示了两栖动物 Ilp1 和脊椎动物胰岛素样生长因子 1 （Igf1） 在预测结构、对身体生长和氨基酸代谢的影响以及与 Igf 结合蛋白的相互作用方面的相似性。这些发现表明，涉及 Pdx 对胰岛素基因表达的调节影响的进化改变可能有助于脊椎动物消化系统的发育。