Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229-3039, USA.
Development. 2010 Dec;137(23):3953-63. doi: 10.1242/dev.054775. Epub 2010 Oct 27.
Kruppel-like transcription factors (Klfs) are essential for the induction and maintenance of pluripotency of embryonic stem cells (ESCs), yet little is known about their roles in establishing the three lineages of the pre-implantation embryo. Here, we show that Klf5 is required for the formation of the trophectoderm (TE) and the inner cell mass (ICM), and for repressing primitive endoderm (PE) development. Although cell polarity appeared normal, Klf5 mutant embryos arrested at the blastocyst stage and failed to hatch due to defective TE development. Klf5 acted cell-autonomously in the TE, downstream of Fgf4 and upstream of Cdx2, Eomes and Krt8. In the ICM, loss of Klf5 resulted in reduced expression of pluripotency markers Oct4 and Nanog, but led to increased Sox17 expression in the PE, suggesting that Klf5 suppresses the PE lineage. Consistent with this, overexpression of Klf5 in transgenic embryos was sufficient to suppress the Sox17(+) PE lineage in the ICM. Klf5 overexpression led to a dose-dependent decrease in Sox17 promoter activity in reporter assays in cultured cells. Moreover, in chimeric embryos, Klf5(-/-) cells preferentially contributed to the Sox17(+) PE lineage and Cdx2 expression was not rescued in Klf5(-/-) outer cells. Finally, outgrowths from Klf5(-/-) embryos failed to form an ICM/pluripotent colony, had very few Oct4(+) or Cdx2(+) cells, but showed an increase in the percentage of Sox17(+) PE cells. These findings demonstrate that Klf5 is a dynamic regulator of all three lineages in the pre-implantation embryo by promoting the TE and epiblast lineages while suppressing the PE lineage.
Kruppel 样转录因子（Klfs）对于胚胎干细胞（ESCs）的多能性的诱导和维持至关重要，但对于它们在建立植入前胚胎的三个谱系中的作用知之甚少。在这里，我们表明 Klf5 对于滋养外胚层（TE）和内细胞团（ICM）的形成以及原始内胚层（PE）发育的抑制是必需的。尽管细胞极性似乎正常，但 Klf5 突变体胚胎在胚泡阶段停滞，由于 TE 发育缺陷而无法孵化。 Klf5 在 TE 中自主作用，在 Fgf4 的下游和 Cdx2、Eomes 和 Krt8 的上游。在 ICM 中，Klf5 的缺失导致多能性标记物 Oct4 和 Nanog 的表达减少，但导致 PE 中 Sox17 的表达增加，表明 Klf5 抑制 PE 谱系。与此一致，在转基因胚胎中超表达 Klf5 足以抑制 ICM 中的 Sox17(+)PE 谱系。 Klf5 过表达导致在培养细胞中的报告基因检测中 Sox17 启动子活性呈剂量依赖性下降。此外，在嵌合胚胎中，Klf5(-/-)细胞优先贡献 Sox17(+)PE 谱系，并且 Klf5(-/-)外细胞中的 Cdx2 表达未被挽救。最后，Klf5(-/-)胚胎的外生体未能形成 ICM/多能集落，仅有很少的 Oct4(+)或 Cdx2(+)细胞，但 Sox17(+)PE 细胞的百分比增加。这些发现表明，Klf5 通过促进 TE 和外胚层谱系，同时抑制 PE 谱系，成为植入前胚胎中所有三个谱系的动态调节剂。
