Blum Martin, Schweickert Axel, Vick Philipp, Wright Christopher V E, Danilchik Michael V
University of Hohenheim, Institute of Zoology (220), Garbenstrasse 30, D-70593 Stuttgart, Germany.
University of Hohenheim, Institute of Zoology (220), Garbenstrasse 30, D-70593 Stuttgart, Germany.
Dev Biol. 2014 Sep 1;393(1):109-23. doi: 10.1016/j.ydbio.2014.06.014. Epub 2014 Jun 24.
Asymmetric development of the vertebrate embryo has fascinated embryologists for over a century. Much has been learned since the asymmetric Nodal signaling cascade in the left lateral plate mesoderm was detected, and began to be unraveled over the past decade or two. When and how symmetry is initially broken, however, has remained a matter of debate. Two essentially mutually exclusive models prevail. Cilia-driven leftward flow of extracellular fluids occurs in mammalian, fish and amphibian embryos. A great deal of experimental evidence indicates that this flow is indeed required for symmetry breaking. An alternative model has argued, however, that flow simply acts as an amplification step for early asymmetric cues generated by ion flux during the first cleavage divisions. In this review we critically evaluate the experimental basis of both models. Although a number of open questions persist, the available evidence is best compatible with flow-based symmetry breakage as the archetypical mode of symmetry breakage.
脊椎动物胚胎的不对称发育在一个多世纪以来一直吸引着胚胎学家。自从在左侧侧板中胚层检测到不对称的Nodal信号级联反应，并在过去一二十年开始被揭示以来，人们已经了解了很多。然而，对称性最初何时以及如何被打破，仍然是一个有争议的问题。目前有两种基本相互排斥的模型。在哺乳动物、鱼类和两栖动物胚胎中会发生由纤毛驱动的细胞外液向左流动。大量实验证据表明，这种流动确实是打破对称性所必需的。然而，另一种模型认为，流动仅仅是第一次卵裂过程中离子通量产生的早期不对称线索的放大步骤。在这篇综述中，我们批判性地评估了这两种模型的实验基础。尽管仍然存在许多未解决的问题，但现有证据最符合基于流动的对称性打破作为对称性打破的典型模式。
