Srinivas Shankar, Rodriguez Tristan, Clements Melanie, Smith James C, Beddington Rosa S P
Division of Mammalian Development, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
Development. 2004 Mar;131(5):1157-64. doi: 10.1242/dev.01005.
The anterior visceral endoderm (AVE) of the mouse embryo is a specialised extra-embryonic tissue that is essential for anterior patterning of the embryo. It is characterised by the expression of anterior markers such as Hex, Cerberus-like and Lhx1. At pre-gastrula stages, cells of the AVE are initially located at the distal tip of the embryo, but they then move unilaterally to the future anterior. This movement is essential for converting the existing proximodistal axis into an anteroposterior axis. To investigate this process, we developed a culture system capable of imaging embryos in real time with single cell resolution. Our results show that AVE cells continuously change shape and project filopodial processes in their direction of motion, suggesting that they are actively migrating. Their proximal movement stops abruptly at the junction of the epiblast and extra-embryonic ectoderm, whereupon they move laterally. Confocal microscope images show that AVE cells migrate as a single layer in direct contact with the epiblast, suggesting that this tissue might provide directional cues. Together, these results show that the anteroposterior axis is correctly positioned by the active movement of cells of the AVE in response to cues from their environment, and by a 'barrier' to their movement that provides an endpoint for this migration.
小鼠胚胎的前脏内胚层（AVE）是一种特殊的胚外组织，对胚胎的前部模式形成至关重要。它的特征是表达如Hex、Cerberus样蛋白和Lhx1等前部标记物。在原肠胚形成前阶段，AVE的细胞最初位于胚胎的远端，但随后它们会单侧移动到未来的前部。这种移动对于将现有的近远轴转化为前后轴至关重要。为了研究这个过程，我们开发了一种能够以单细胞分辨率实时成像胚胎的培养系统。我们的结果表明，AVE细胞不断改变形状，并在其运动方向上伸出丝状伪足，这表明它们在积极迁移。它们向近端的移动在胚泡和胚外外胚层的交界处突然停止，随后它们横向移动。共聚焦显微镜图像显示，AVE细胞作为单层与胚泡直接接触迁移，这表明该组织可能提供方向线索。总之，这些结果表明，前后轴是通过AVE细胞对来自其环境的线索的主动运动以及为这种迁移提供终点的运动“屏障”而正确定位的。
