Background: In the ascidian Ciona intestinalis, the digestive tract, an essential system for animals, develops during metamorphosis from the two primordial tissues, the endoderm and endodermal strand, located in the larval trunk and tail, respectively. However, it has been largely unknown how the digestive tract develops from these primordial tissues. We examined the metamorphosing larvae for the tubular formation of the digestive tract, focusing on the epithelial organization of the endoderm, by combined confocal microscopy and computational rendering. Results: The tubular structure of the esophagus to the stomach was formed through the folding and closure of the endodermal epithelia in the central-to-right posterior trunk. By contrast, the intestine was formed in the left posterior trunk through the accumulation and rearrangement of the cells originated from the endodermal strand. This was confirmed by the cell-tracing experiment using Kaede expression construct driven in the endodermal strand. Thus, the tubular formation of the digestive tract in C. intestinalis includes distinct morphogenetic processes and cell lineages between its anterior and posterior parts. Conclusion: This study provides the first detailed description of the digestive tract morphogenesis in C. intestinalis and serves as an important basis toward thorough understanding of its digestive tract development. Developmental Dynamics, 242:1172-1183, 2013. Key findings: In Ciona intestinalis, the basic architecture of the digestive tract is formed by the stage35 when the tadpole tail is absorbed. The anterior digestive tract, including the oesophagus and the stomach, is formed through the folding and closure of the endoderm. The posterior digestive tract, the intestine, is formed through accumulation and rearrangement of the cells of the endodermal strand origin.
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