哺乳动物的卵细胞受精几天后就会形成囊胚，随后不到100个细胞所形成的空心球体结构会分裂成为外层结构并继而形成胎盘，中间的小型细胞簇形成胚胎组织。
近日，来自荷兰马斯特里赫特大学的研究人员在实验室里对干细胞系单独培养，利用工程化技术首次诱导精子和卵细胞以外的干细胞系进行自我组装，最终形成类似胚胎组织。首先，研究人员对一组与胎盘相对应的小鼠干细胞进行研究，使其自组装成为原型胚胎结构，结果当其被植入到小鼠子宫内时就能够开始妊娠。在自然胚胎中，相同的干细胞能在三维空间中相互交流，此前我们无法理解其中涉及的机制。这项新的研究能够模拟这个过程，让干细胞自发地按照在子宫内的模式进行排列，指导胚胎干细胞进行繁殖、组装并且植入子宫内。然而，该研究还无法利用干细胞制造出有活力的胚胎组织。
研究人员Nicolas Rivron表示，这些早期的胚胎有着所有能形成完整机体的细胞类型，将帮助研究人员更好地理解机体的生育力及早期生命阶段的发生机制，并为解决生育问题、提高辅助生殖效率、探究先天性疾病的疗法提供重要研究模型。
推荐阅读原文：
Blastocyst-like structures generated solely from stem cells.
The blastocyst (the early mammalian embryo) forms all embryonic and extra-embryonic tissues, including the placenta. It consists of a spherical thin-walled layer, known as the trophectoderm, that surrounds a fluid-filled cavity sheltering the embryonic cells. From mouse blastocysts, it is possible to derive both trophoblast and embryonic stem-cell lines, which are in vitro analogues of the trophectoderm and embryonic compartments, respectively. Here we report that trophoblast and embryonic stem cells cooperate in vitro to form structures that morphologically and transcriptionally resemble embryonic day 3.5 blastocysts, termed blastoids. Like blastocysts, blastoids form from inductive signals that originate from the inner embryonic cells and drive the development of the outer trophectoderm. The nature and function of these signals have been largely unexplored. Genetically and physically uncoupling the embryonic and trophectoderm compartments, along with single-cell transcriptomics, reveals the extensive inventory of embryonic inductions. We specifically show that the embryonic cells maintain trophoblast proliferation and self-renewal, while fine-tuning trophoblast epithelial morphogenesis in part via a BMP4/Nodal–KLF6 axis. Although blastoids do not support the development of bona fide embryos, we demonstrate that embryonic inductions are crucial to form a trophectoderm state that robustly implants and triggers decidualization in utero. Thus, at this stage, the nascent embryo fuels trophectoderm development and implantation.
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