Bilateria share sequential steps in their digestive systems, and digestion occurs in a pre-absorption step within a chamber-like structure. Previous studies on the ascidian Ciona intestinalis type A, an evolutionary research model of vertebrate organs, revealed that Ciona homologs of pancreas-related exocrine digestive enzymes (XDEs) are exclusively expressed in the chamber-like bulging stomach. In the development of the gastrointestinal tract, genes for the pancreas-related transcription factors, namely Ptf1a, Nr5a2, and Pdx, are expressed near the stomach. Recent organ/tissue RNA-seq studies on two Ciona species reported that transcripts of the XDE homologs exist in the intestinal regions, as well as in the stomach. In the present study, we investigated the spatial gene expression of XDE homologs in the gastrointestinal region of the C. intestinalis type A. Whole-mount in situ hybridization using adult and juvenile specimens revealed apparent expression signals of XDE homologs in a small number of gastrointestinal epithelial cells. Furthermore, two pancreas-related transcription factor genes, Nr5a2 and Pdx, exhibited multi-regional expression along the Ciona juvenile intestines. These results imply that ascidians may form multiple digestive regions corresponding to the vertebrate pancreas.

两侧对称动物的消化系统共享连续的步骤，消化发生在类似室的结构内的预吸收步骤中。先前对海鞘Ciona Enteris A型（一种脊椎动物器官进化研究模型）的研究表明，与胰腺相关的外分泌消化酶（XDE）的Ciona同源物仅在室状鼓起的胃中表达。在胃肠道的发育过程中，胰腺相关转录因子的基因，即Ptf1a、Nr5a2和Pdx在胃附近表达。最近对两种Ciona物种的器官/组织 RNA-seq 研究报告称，XDE 同源物的转录物存在于肠道区域以及胃中。在本研究中，我们研究了A 型肠杆菌胃肠道中 XDE 同源物的空间基因表达。使用成年和幼年标本的整体原位杂交揭示了少数胃肠道中 XDE 同源物的明显表达信号上皮细胞。此外，两个胰腺相关转录因子基因Nr5a2和Pdx在海鞘幼年肠道中表现出多区域表达。这些结果意味着海鞘可能形成与脊椎动物胰腺相对应的多个消化区域。