Foley Ann C, Korol Oksana, Timmer Anjuli M, Mercola Mark
Burnham Institute for Medical Research, 10901 N. Torrey Pines Road, La Jolla, CA 92037, USA.
Dev Biol. 2007 Mar 1;303(1):57-65. doi: 10.1016/j.ydbio.2006.10.033. Epub 2006 Oct 26.
The TGFbeta family member Nodal has been implicated in heart induction through misexpression of a dominant negative version of the type I Nodal receptor (Alk4) and targeted deletion of the co-receptor Cripto in murine ESCs and mouse embryos; however, whether Nodal acts directly or indirectly to induce heart tissue or interacts with other signaling molecules or pathways remained unclear. Here we present Xenopus embryological studies demonstrating an unforeseen role for the DAN family protein Cerberus within presumptive foregut endoderm as essential for differentiation of cardiac mesoderm in response to Nodal. Ectopic activation of Nodal signaling in non-cardiogenic ventroposterior mesendoderm, either by misexpression of the Nodal homologue XNr1 together with Cripto or by a constitutively active Alk4 (caAlk4), induced both cardiac markers and Cerberus. Mosaic lineage tracing studies revealed that Nodal/Cripto and caAlk4 induced cardiac markers cell non-autonomously, thus supporting the idea that Cerberus or another diffusible factor is an essential mediator of Nodal-induced cardiogenesis. Cerberus alone was found sufficient to initiate cardiogenesis at a distance from its site of synthesis. Conversely, morpholino-mediated specific knockdown of Cerberus reduced both endogenous cardiomyogenesis and ectopic heart induction resulting from misactivation of Nodal/Cripto signaling. Since the specific knockdown of Cerberus did not abrogate heart induction by the Wnt antagonist Dkk1, Nodal/Cripto and Wnt antagonists appear to initiate cardiogenesis through distinct pathways. This idea was further supported by the combinatorial effect of morpholino-medicated knockdown of Cerberus and Hex, which is required for Dkk1-induced cardiogenesis, and the differential roles of essential downstream effectors: Nodal pathway activation did not induce the transcriptional repressor Hex while Dkk-1 did not induce Cerberus. These studies demonstrated that cardiogenesis in mesoderm depends on Nodal-mediated induction of Cerberus in underlying endoderm, and that this pathway functions in a pathway parallel to cardiogenesis initiated through the induction of Hex by Wnt antagonists. Both pathways operate in endoderm to initiate cardiogenesis in overlying mesoderm.
转化生长因子β（TGFβ）家族成员Nodal已被证明与心脏诱导有关，这是通过在小鼠胚胎干细胞和小鼠胚胎中错误表达I型Nodal受体（Alk4）的显性负性版本以及靶向缺失共受体Cripto实现的；然而，Nodal是直接还是间接诱导心脏组织，或者是否与其他信号分子或信号通路相互作用，仍不清楚。在此，我们展示了非洲爪蟾胚胎学研究，证明了DAN家族蛋白Cerberus在假定的前肠内胚层中具有意想不到的作用，它对于响应Nodal诱导心脏中胚层的分化至关重要。通过Nodal同源物XNr1与Cripto的错误表达或组成型活性Alk4（caAlk4），在非心脏源性腹侧后中胚层中异位激活Nodal信号，可诱导心脏标志物和Cerberus。嵌合谱系追踪研究表明，Nodal/Cripto和caAlk4非自主地诱导心脏标志物，从而支持Cerberus或另一种可扩散因子是Nodal诱导心脏发生的重要介质这一观点。单独的Cerberus就足以在远离其合成位点的地方启动心脏发生。相反，吗啉代介导的Cerberus特异性敲低减少了内源性心肌发生以及由Nodal/Cripto信号错误激活导致的异位心脏诱导。由于Cerberus的特异性敲低并没有消除Wnt拮抗剂Dkk1诱导的心脏诱导，Nodal/Cripto和Wnt拮抗剂似乎通过不同的途径启动心脏发生。吗啉代介导的Cerberus和Hex敲低的组合效应进一步支持了这一观点，Hex是Dkk1诱导心脏发生所必需的，以及重要下游效应器的不同作用：Nodal通路激活不会诱导转录抑制因子Hex，而Dkk-1不会诱导Cerberus。这些研究表明，中胚层中的心脏发生依赖于Nodal介导的内胚层中Cerberus的诱导，并且该途径在与通过Wnt拮抗剂诱导Hex启动的心脏发生平行的途径中起作用。这两条途径都在内胚层中起作用，以启动上覆中胚层中的心脏发生。
