Background Wnt/β-catenin (or canonical) signalling pathway activity is necessary and used independently several times for specification of vegetal fate and endoderm, gut differentiation, maintenance of epithelium in adult intestine and the development of gut-derived organs in various vertebrate and non-vertebrate organisms. However, its conservation in later stages of digestive tract development still remains questionable due to the lack of detailed data, mainly from Spiralia. Results Here we characterize the Pdu-Tcf gene, a Tcf/LEF orthologue and a component of Wnt/β-catenin pathway from Platynereis dumerilii, a spiralian, marine annelid worm. Pdu-Tcf undergoes extensive alternative splicing in the C-terminal region of the gene generating as many as eight mRNA isoforms some of which differ in the presence or absence of a C-clamp domain which suggests a distinct DNA binding activity of individual protein variants. Pdu-Tcf is broadly expressed throughout development which is indicative of many functions. One of the most prominent domains that exhibits rather strong Pdu-Tcf expression is in the putative precursors of endodermal gut cells which are detected after 72 h post-fertilization (hpf). At day 5 post-fertilization (dpf), Pdu-Tcf is expressed in the hindgut and pharynx (foregut), whereas at 7 dpf stage, it is strongly transcribed in the now-cellularized midgut for the first time. In order to gain insight into the role of Wnt/β-catenin signalling, we disrupted its activity using pharmacological inhibitors between day 5 and 7 of development. The inhibition of Wnt/β-catenin signalling led to the loss of midgut marker genes Subtilisin-1, Subtilisin-2, α-Amylase and Otx along with a drop in β-catenin protein levels, Axin expression in the gut and nearly the complete loss of proliferative activity throughout the body of larva. At the same time, a hindgut marker gene Legumain was expanded to the midgut compartment under the same conditions. Conclusions Our findings suggest that high Wnt/β-catenin signalling in the midgut might be necessary for proper differentiation of the endoderm to an epithelium capable of secreting digestive enzymes. Together, our data provide evidence for the role of Wnt/β-catenin signalling in gut differentiation in Platynereis.

中文翻译：

---

Wnt/β-连环蛋白信号是海洋环节动物 Platynereis dumerilii 肠道分化所必需的。

背景 Wnt/β-连环蛋白（或经典）信号通路活性对于植物命运和内胚层的规范、肠道分化、成人肠道上皮的维持以及各种脊椎动物和非- 脊椎动物。然而，由于缺乏详细的数据，主要来自螺旋藻，它在消化道发育后期的保护仍然存在疑问。结果 在这里，我们描述了 Pdu-Tcf 基因、Tcf/LEF 直系同源物和来自 Platynereis dumerilii、一种螺旋形海洋环节动物蠕虫的 Wnt/β-连环蛋白途径的一个组成部分。Pdu-Tcf 在基因的 C 末端区域经历广泛的可变剪接，产生多达 8 种 mRNA 同种型，其中一些在存在或不存在 C-clamp 结构域时有所不同，这表明单个蛋白质变体具有不同的 DNA 结合活性。Pdu-Tcf 在整个开发过程中广泛表达，这表明了许多功能。表现出相当强的 Pdu-Tcf 表达的最突出的领域之一是在受精后 72 小时 (hpf) 后检测到的内胚层肠道细胞的假定前体中。在受精后第 5 天 (dpf)，Pdu-Tcf 在后肠和咽部（前肠）中表达，而在 7 dpf 阶段，它首次在现在细胞化的中肠中强烈转录。为了深入了解 Wnt/β-catenin 信号传导的作用，我们在开发的第 5 天和第 7 天之间使用药理学抑制剂破坏了它的活性。Wnt/β-catenin 信号传导的抑制导致中肠标记基因 Subtilisin-1、Subtilisin-2、α-淀粉酶和 Otx 的丢失以及 β-catenin 蛋白水平、肠道中 Axin 表达和几乎完整的整个幼虫体内的增殖活性丧失。同时，在相同条件下将后肠标记基因Legumain扩展到中肠室。结论 我们的研究结果表明，中肠中的高 Wnt/β-catenin 信号传导可能是内胚层适当分化为能够分泌消化酶的上皮细胞所必需的。总之，我们的数据为 Wnt/β-catenin 信号传导在扁桃体肠道分化中的作用提供了证据。