Liu Shichao, Bou Gerelchimeg, Zhao Jianchao, Guo Shimeng, Guo Jia, Weng Xiaogang, Yin Zhi, Liu Zhonghua
College of Life Science, Northeast Agricultural University of China, Harbin, China.
Key Laboratory of Animal Cellular and Genetic Engineering of Heilongjiang Province, Northeast Agricultural University, Harbin, China.
Mol Reprod Dev. 2018 Jul;85(7):590-598. doi: 10.1002/mrd.22994. Epub 2018 Jul 16.
Upregulation of Cdx2 expression in outer cells is a key event responsible for cell lineage segregation between the inner cell mass and the trophoderm (TE) in mouse morula-stage embryos. In TE cells, polarization can regulate Hippo and Rho-associated kinase (Rho-ROCK) signaling to induce the nuclear location of YAP, which has been demonstrated to further induce the expression of Cdx2. However, we found that CDX2 expression could not be detected in the outer cells of porcine morula-stage embryos but only in some TE cells at the early blastocyst stage. The biological significance and the regulation mechanism of this species-specific CDX2 expression pattern have still not been determined. We show here that an asynchronous CDX2 expression pattern exists in porcine TE cells during the development of the blastocyst. We demonstrate that CDX2 expression in porcine TE cells depends on the nuclear localization of YAP and polarization of the embryo through Y27632 treatment. We found that the polarization process in the morula to the late blastocyst stage porcine embryos was asynchronous, which was revealed by the apical localization of phosphorylated EZRIN staining. Artificially enhancing the number of polarized blastomeres by culturing the separated blastomeres of four-cell stage porcine embryos resulted in increased CDX2-positive cell numbers. These results indicate that the mechanism of CDX2 expression regulation is conserved, but the polarization progress is not conserved between the pig and the mouse, and results in a species-specific trophoblast determination progress model.
外层细胞中Cdx2表达的上调是小鼠桑葚胚阶段胚胎内细胞团和滋养层（TE）之间细胞谱系分离的关键事件。在TE细胞中，极化可调节Hippo和Rho相关激酶（Rho-ROCK）信号传导，以诱导YAP的核定位，这已被证明可进一步诱导Cdx2的表达。然而，我们发现猪桑葚胚阶段胚胎的外层细胞中检测不到CDX2表达，而仅在早期囊胚阶段的一些TE细胞中检测到。这种物种特异性CDX2表达模式的生物学意义和调控机制仍未确定。我们在此表明，猪TE细胞在囊胚发育过程中存在异步CDX2表达模式。我们证明，猪TE细胞中CDX2的表达依赖于YAP的核定位以及通过Y27632处理使胚胎极化。我们发现，猪胚胎从桑葚胚到晚期囊胚阶段的极化过程是异步的，这通过磷酸化EZRIN染色的顶端定位得以揭示。通过培养四细胞阶段猪胚胎的分离卵裂球人为增加极化卵裂球的数量，导致CDX2阳性细胞数量增加。这些结果表明，CDX2表达调控机制是保守的，但猪和小鼠之间的极化进程并不保守，从而导致了物种特异性的滋养层决定进程模型。
