Division of Animal Sciences, School of Biosciences, University of Nottingham, College Rd, LE12 5RD, Loughborough, UK.
Division of Animal Sciences, School of Biosciences, University of Nottingham, College Rd, LE12 5RD, Loughborough, UK.
Dev Biol. 2014 Mar 1;387(1):15-27. doi: 10.1016/j.ydbio.2014.01.008. Epub 2014 Jan 18.
The crosstalk between the epiblast and the trophoblast is critical in supporting the early stages of conceptus development. FGF4 and BMP4 are inductive signals that participate in the communication between the epiblast and the extraembryonic ectoderm (ExE) of the developing mouse embryo. Importantly, however, it is unknown whether a similar crosstalk operates in species that lack a discernible ExE and develop a mammotypical embryonic disc (ED). Here we investigated the crosstalk between the epiblast and the trophectoderm (TE) during pig embryo elongation. FGF4 ligand and FGFR2 were detected primarily on the plasma membrane of TE cells of peri-elongation embryos. The binding of this growth factor to its receptor triggered a signal transduction response evidenced by an increase in phosphorylated MAPK/ERK. Particular enrichment was detected in the periphery of the ED in early ovoid embryos, indicating that active FGF signalling was operating during this stage. Gene expression analysis shows that CDX2 and ELF5, two genes expressed in the mouse ExE, are only co-expressed in the Rauber's layer, but not in the pig mural TE. Interestingly, these genes were detected in the nascent mesoderm of early gastrulating embryos. Analysis of BMP4 expression by in situ hybridisation shows that this growth factor is produced by nascent mesoderm cells. A functional test in differentiating epiblast shows that CDX2 and ELF5 are activated in response to BMP4. Furthermore, the effects of BMP4 were also demonstrated in the neighbouring TE cells, as demonstrated by an increase in phosphorylated SMAD1/5/8. These results show that BMP4 produced in the extraembryonic mesoderm is directly influencing the SMAD response in the TE of elongating embryos. These results demonstrate that paracrine signals from the embryo, represented by FGF4 and BMP4, induce a response in the TE prior to the extensive elongation. The study also confirms that expression of CDX2 and ELF5 is not conserved in the mural TE, indicating that although the signals that coordinate conceptus growth are similar between rodents and pigs, the gene regulatory network of the trophoblast lineage is not conserved in these species.
内胚层和滋养层之间的串扰对于支持胚胎早期发育至关重要。FGF4 和 BMP4 是参与发育中的小鼠胚胎内胚层和胚胎外胚层（ExE）之间通讯的诱导信号。然而，重要的是，在缺乏明显的 ExE 并发育出典型哺乳动物胚胎盘（ED）的物种中，是否存在类似的串扰尚不清楚。在这里，我们研究了猪胚胎伸长过程中内胚层和滋养层（TE）之间的串扰。在伸长前胚胎中，FGF4 配体和 FGFR2 主要检测到 TE 细胞的质膜上。这种生长因子与其受体的结合触发了信号转导反应，表现为磷酸化 MAPK/ERK 的增加。在早期卵球形胚胎的 ED 周边检测到特定的富集，表明在这个阶段活跃的 FGF 信号正在起作用。基因表达分析表明，在小鼠 ExE 中表达的两个基因 CDX2 和 ELF5 仅在 Rauber 层中共同表达，而不在猪壁滋养 TE 中表达。有趣的是，这些基因在早期原肠胚形成的中胚层中被检测到。原位杂交分析显示 BMP4 表达表明这种生长因子由新生中胚层细胞产生。在分化的内胚层中的功能测试表明，CDX2 和 ELF5 对 BMP4 有反应。此外，BMP4 的作用也在邻近的 TE 细胞中得到证实，表现为磷酸化 SMAD1/5/8 的增加。这些结果表明，胚外中胚层产生的 BMP4 直接影响伸长胚胎 TE 中的 SMAD 反应。这些结果表明，代表 FGF4 和 BMP4 的胚胎旁分泌信号在 TE 广泛伸长之前诱导其反应。该研究还证实，CDX2 和 ELF5 的表达在壁滋养层中没有保守，表明尽管协调胚胎生长的信号在啮齿动物和猪之间相似，但滋养层谱系的基因调控网络在这些物种中并不保守。
