Winklbauer Rudolf, Parent Serge E
University of Toronto, Department of Cell and Systems Biology, 25 Harbord Street, Toronto, ON M5S 3G5, Canada.
Mech Dev. 2017 Apr;144(Pt A):81-91. doi: 10.1016/j.mod.2016.09.003. Epub 2016 Sep 30.
Adhesion differences are the main driver of cell sorting and related processes such as boundary formation or tissue positioning. In the early amphibian embryo, graded variations in cadherin density and localized expression of adhesion-modulating factors are associated with regional differences in adhesive properties including overall adhesion strength. The role of these differences in embryonic boundary formation has not been studied extensively, but available evidence suggests that adhesion strength differentials are not essential. On the other hand, the inside-out positioning of the germ layers is correlated with adhesion strength, although the biological significance of this effect is unclear. By contrast, the positioning of dorsal mesoderm tissues along the anterior-posterior body axis is essential for axis elongation, but the underlying sorting mechanism is not correlated with adhesion strength, and may rely on specific cell adhesion. Formation of the ectoderm-mesoderm boundary is the best understood sorting related process in the frog embryo. It relies on contact-induced cell repulsion at the tissue interface, driven by Eph-ephrin signaling and paraxial protocadherin-dependent self/non-self recognition.
黏附差异是细胞分选及相关过程（如边界形成或组织定位）的主要驱动因素。在早期两栖类胚胎中，钙黏蛋白密度的梯度变化以及黏附调节因子的局部表达与包括整体黏附强度在内的黏附特性的区域差异相关。这些差异在胚胎边界形成中的作用尚未得到广泛研究，但现有证据表明黏附强度差异并非必不可少。另一方面，胚层的由内向外定位与黏附强度相关，尽管这种效应的生物学意义尚不清楚。相比之下，背侧中胚层组织沿前后体轴的定位对于轴伸长至关重要，但其潜在的分选机制与黏附强度无关，可能依赖于特定的细胞黏附。外胚层 - 中胚层边界的形成是青蛙胚胎中最容易理解的与分选相关的过程。它依赖于组织界面处由Eph - Ephrin信号传导和近轴原钙黏蛋白依赖性自我/非自我识别驱动的接触诱导细胞排斥。
