Kevin Eggan2014-02-27 12:07 PM

Analysis of human embryos from zygote to blastocyst reveals distinct gene expression patterns relative to the mouse. 对人类胚胎从受精卵到囊胚的分析揭示了人类相对于小鼠来说不同的基因表达方式 

Abstract
Early mammalian embryogenesis is controlled by mechanisms governing the balance between pluripotency and differentiation. The expression of early lineage-specific genes can vary significantly between species, with implications for developmental control and stem cell derivation. However, the mechanisms involved in patterning the human embryo are still unclear. We analyzed the appearance and localization of lineage-specific transcription factors in staged preimplantation human embryos from the zygote until the blastocyst. We observed that the pluripotency-associated transcription factor OCT4 was initially expressed in 8-cell embryos at 3 days post-fertilization (dpf), and restricted to the inner cell mass (ICM) in 128–256 cell blastocysts (6 dpf), approximately 2 days later than the mouse. The trophectoderm (TE)-associated transcription factor CDX2 was upregulated in 5 dpf blastocysts and initially coincident with OCT4, indicating a lag in CDX2 initiation in the TE lineage, relative to the mouse. Once established, the TE expressed intracellular and cell-surface proteins cytokeratin-7 (CK7) and fibroblast growth factor receptor-1 (FGFR1), which are thought to be specific to post-implantation human trophoblast progenitor cells. The primitive endoderm (PE)-associated transcription factor SOX17 was initially heterogeneously expressed in the ICM where it co-localized with a sub-set of OCT4 expressing cells at 4–5 dpf. SOX17 was progressively restricted to the PE adjacent to the blastocoel cavity together with the transcription factor GATA6 by 6 dpf. We observed low levels of Laminin expression in the human PE, though this basement membrane component is thought to play an important role in mouse PE cell sorting, suggesting divergence in differentiation mechanisms between species. Additionally, while stem cell lines representing the three distinct cell types that comprise a mouse blastocyst have been established, the identity of cell types that emerge during early human embryonic stem cell derivation is unclear. We observed that derivation from plating intact human blastocysts resulted predominantly in the outgrowth of TE-like cells, which impairs human embryonic stem cell derivation. Altogether, our findings provide important insight into developmental patterning of preimplantation human embryos with potential consequences for stem cell derivation.

论文摘要

哺乳动物早期胚胎发育由监管多能性和分化间平衡的机制所控制。早期谱系特异性基因表达在物种间可能产生显著差别且对发育控制和干细胞衍生产生影响。然而我们对涉及人类胚胎形成模式的机制仍不清楚。我们分析了未植入人类胚胎从受精卵直到囊胚阶段的谱系特异性转录因子的外观和定位。我们发现多能性相关的转录因子OCT4最初于受精后3天在8个细胞胚胎中表达(DPF),且在受精后6天仅局限于内细胞团(ICM 中的128-256个细胞囊胚(6 DPF),这大约比小鼠慢2天左右。滋养外胚层(TE)相关的转录因子CDX2在受精后5天(5 DPF)于囊胚中上调并初步与OCT4一致,这表明了相对于小鼠来说,人体中启始于滋养外胚层(TE)谱系的CDX2的滞后。 一旦建立,滋养外胚层(TE)表达了细胞内和细胞表面蛋白细胞的角蛋白7CK7)和成纤维细胞生长因子受体-1FGFR1),这被认为是用来特定针对植入后人类(胚胎)滋养层祖细胞的。原始内胚层(PE)相关的转录因子SOX17最初在内细胞团(ICM)中异质表达,它在内细胞团(ICM)中与OCT4表达细胞的某个子集在受精后45天(4-5 DPF)共同定位。SOX17与转录因子GATA6一起在受精后6天( 6 DPF)被逐步限制在相邻于囊胚腔的原始内胚层(PE)中。我们在人类原始内胚层(PE)中观察到层粘连蛋白的低水平表达,尽管此基底膜成分被认为在小鼠原始内胚层(PE)细胞分选中起重要作用,这表明了物种间分化机制出现的分歧。此外,虽然干细胞系代表了包括小鼠胚泡已经建立的三种不同细胞类型, 然而我们对早期人类胚胎干细胞衍生的细胞类型特性仍不清楚。我们观察到通过覆盖完整人囊胚所得的衍生物显著导致类滋养外胚层(TE)细胞的生长,这会损害人类胚胎干细胞衍生。综上所述,我们的研究结果为植入前人类胚胎发育模式及其对干细胞派生产生的潜在影响提供了重要启示。

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Kevin Eggan

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