Laboratory of Animal Breeding and Reproduction, Research Faculty of Agriculture, Hokkaido University, Kita-ku, Kita 9, Nishi 9, Sapporo 060-8589, Japan.
Laboratory of Theriogenology, Department of Veterinary Clinical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan.
J Biol Chem. 2019 Dec 13;294(50):19209-19223. doi: 10.1074/jbc.RA119.010746. Epub 2019 Nov 8.
Which comes first: tissue structure or cell differentiation? Although different cell types establish distinct structures delineating the inside and outside of an embryo, they progressively become specified by the blastocyst stage, when two types of cell lineages are formed: the inner cell mass (ICM) and the trophectoderm (TE). This inside-outside aspect can be experimentally converted by the isolation of the ICM from a blastocyst, leading to externalization of the blastomeres composing the outermost layer of the ICM. Here, we investigated the totipotency of isolated mouse and bovine ICMs to determine whether they are competent for TE regeneration. Surprisingly, a calf was generated from the bovine isolated ICM with re-formed blastocoel (re-iICM), but no mouse re-iICMs developed to term. To further explore the cause of difference in developmental competency between the mouse and bovine re-iICMs, we investigated the SOX17 protein expression that is a representative molecular marker of primitive endoderm. The localization pattern of SOX17 was totally different between mouse and bovine embryos. Particularly, the ectopic SOX17 localization in the TE might be associated with lethality of mouse re-iICMs. Meanwhile, transcriptome sequencing revealed that some of the bovine re-iICMs showed transcriptional patterns of TE-specific genes similar to those of whole blastocysts. Our findings suggest that TE regeneration competency is maintained longer in bovine ICMs than in mouse ICMs and provide evidence that the ICM/TE cell fate decision is influenced by structural determinants, including positional information of each blastomere in mammalian embryos.
组织结构还是细胞分化先出现？尽管不同类型的细胞形成了明确的结构来界定胚胎的内外，但它们在囊胚阶段逐渐被特化，此时形成了两种细胞谱系：内细胞团（ICM）和滋养外胚层（TE）。这种内外的特征可以通过从囊胚中分离 ICM 来实验性地改变，导致构成 ICM 最外层的卵裂球的外部化。在这里，我们研究了分离的小鼠和牛 ICM 的全能性，以确定它们是否有能力进行 TE 再生。令人惊讶的是，从牛分离的 ICM 中可以生成小牛（re-iICM），但没有小鼠 re-iICM 发育到足月。为了进一步探索小鼠和牛 re-iICM 之间发育能力差异的原因，我们研究了 SOX17 蛋白的表达，它是原始内胚层的代表性分子标志物。SOX17 的定位模式在小鼠和牛胚胎之间完全不同。特别是，TE 中 SOX17 的异位定位可能与小鼠 re-iICM 的致死性有关。同时，转录组测序显示，一些牛 re-iICM 表现出与整个囊胚相似的 TE 特异性基因的转录模式。我们的发现表明，牛 ICM 中 TE 再生的能力比小鼠 ICM 中维持得更久，并提供了证据表明 ICM/TE 细胞命运的决定受到结构决定因素的影响，包括哺乳动物胚胎中每个卵裂球的位置信息。
