Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK.
Development. 2012 Jan;139(1):129-39. doi: 10.1242/dev.067702. Epub 2011 Nov 17.
Cell differentiation during pre-implantation mammalian development involves the formation of two extra-embryonic lineages: trophoblast and primitive endoderm (PrE). A subset of cells within the inner cell mass (ICM) of the blastocyst does not respond to differentiation signals and forms the pluripotent epiblast, which gives rise to all of the tissues in the adult body. How this group of cells is set aside remains unknown. Recent studies documented distinct sequential phases of marker expression during the segregation of epiblast and PrE within the ICM. However, the connection between marker expression and lineage commitment remains unclear. Using a fluorescent reporter for PrE, we investigated the plasticity of epiblast and PrE precursors. Our observations reveal that loss of plasticity does not coincide directly with lineage restriction of epiblast and PrE markers, but rather with exclusion of the pluripotency marker Oct4 from the PrE. We note that individual ICM cells can contribute to all three lineages of the blastocyst until peri-implantation. However, epiblast precursors exhibit less plasticity than precursors of PrE, probably owing to differences in responsiveness to extracellular signalling. We therefore propose that the early embryo environment restricts the fate choice of epiblast but not PrE precursors, thus ensuring the formation and preservation of the pluripotent foetal lineage.
滋养层和原始内胚层（PrE）。囊胚的内细胞团（ICM）中的一部分细胞对分化信号没有反应，形成多能的上胚层，它产生成年体内的所有组织。这些细胞是如何被分离出来的仍然未知。最近的研究记录了在 ICM 中胚层和 PrE 的分离过程中标记物表达的不同顺序阶段。然而，标记物表达和谱系决定之间的联系仍然不清楚。我们使用 PrE 的荧光报告基因，研究了上胚层和 PrE 前体的可塑性。我们的观察结果表明，可塑性的丧失并不直接与上胚层和 PrE 标记物的谱系限制相关，而是与 PrE 中的多能性标记物 Oct4 的排除相关。我们注意到，单个 ICM 细胞可以在囊胚的三个谱系中发挥作用，直到着床期。然而，上胚层前体的可塑性比 PrE 前体的可塑性小，这可能是由于对细胞外信号的反应性不同所致。因此，我们提出早期胚胎环境限制了上胚层的命运选择，但不限制 PrE 前体的命运选择，从而确保多能性胎儿谱系的形成和维持。
