Institute of Science and Technology Austria, Klosterneuburg, Austria.
Institute of Science and Technology Austria, Klosterneuburg, Austria.
Dev Biol. 2021 Jun;474:71-81. doi: 10.1016/j.ydbio.2020.12.014. Epub 2020 Dec 19.
During development, a single cell is transformed into a highly complex organism through progressive cell division, specification and rearrangement. An important prerequisite for the emergence of patterns within the developing organism is to establish asymmetries at various scales, ranging from individual cells to the entire embryo, eventually giving rise to the different body structures. This becomes especially apparent during gastrulation, when the earliest major lineage restriction events lead to the formation of the different germ layers. Traditionally, the unfolding of the developmental program from symmetry breaking to germ layer formation has been studied by dissecting the contributions of different signaling pathways and cellular rearrangements in the in vivo context of intact embryos. Recent efforts, using the intrinsic capacity of embryonic stem cells to self-assemble and generate embryo-like structures de novo, have opened new avenues for understanding the many ways by which an embryo can be built and the influence of extrinsic factors therein. Here, we discuss and compare divergent and conserved strategies leading to germ layer formation in embryos as compared to in vitro systems, their upstream molecular cascades and the role of extrinsic factors in this process.
在发育过程中，单个细胞通过渐进的细胞分裂、特化和重排，转化为高度复杂的生物体。在发育生物体中出现模式的一个重要前提条件是在各个尺度上建立不对称性，从单个细胞到整个胚胎，最终导致不同的身体结构。这在原肠胚形成时尤为明显，此时最早的主要谱系限制事件导致不同的胚层形成。传统上，通过在完整胚胎的体内环境中剖析不同信号通路和细胞重排的贡献，研究了从对称性破坏到胚层形成的发育程序的展开。最近的努力利用胚胎干细胞自我组装和从头生成胚胎样结构的内在能力，为理解胚胎构建的多种方式以及其中外在因素的影响开辟了新途径。在这里，我们讨论并比较了导致胚胎与体外系统中胚层形成的不同和保守策略，以及它们的上游分子级联和外在因素在这个过程中的作用。
