IST Austria, Klosterneuburg, Austria.
Elife. 2020 Apr 6;9:e55190. doi: 10.7554/eLife.55190.
Embryonic stem cell cultures are thought to self-organize into embryoid bodies, able to undergo symmetry-breaking, germ layer specification and even morphogenesis. Yet, it is unclear how to reconcile this remarkable self-organization capacity with classical experiments demonstrating key roles for extrinsic biases by maternal factors and/or extraembryonic tissues in embryogenesis. Here, we show that zebrafish embryonic tissue explants, prepared prior to germ layer induction and lacking extraembryonic tissues, can specify all germ layers and form a seemingly complete mesendoderm anlage. Importantly, explant organization requires polarized inheritance of maternal factors from dorsal-marginal regions of the blastoderm. Moreover, induction of endoderm and head-mesoderm, which require peak Nodal-signaling levels, is highly variable in explants, reminiscent of embryos with reduced Nodal signals from the extraembryonic tissues. Together, these data suggest that zebrafish explants do not undergo self-organization, but rather display features of genetically encoded self-assembly, where intrinsic genetic programs control the emergence of order.
胚胎干细胞培养物被认为能够自我组织形成胚状体，能够经历对称破缺、胚层特化甚至形态发生。然而，目前尚不清楚如何将这种非凡的自我组织能力与经典实验相协调，这些经典实验表明母体因素和/或胚胎外组织在胚胎发生中具有关键的外在偏差作用。在这里，我们表明，在诱导胚层之前制备的斑马鱼胚胎组织外植体，缺乏胚胎外组织，可以特化所有胚层并形成似乎完整的中胚层原基。重要的是，外植体的组织形成需要从胚盘的背缘区域有极性地遗传母体因子。此外，内胚层和头中胚层的诱导，需要峰值 Nodal 信号水平，在外植体中变化很大，类似于从胚胎外组织中减少 Nodal 信号的胚胎。总之，这些数据表明，斑马鱼外植体不会经历自我组织，而是表现出遗传编码自组装的特征，其中内在的遗传程序控制着秩序的出现。
