Winklbauer R, Nagel M, Selchow A, Wacker S
Universität zu Köln, Zoologisches Institut, Germany.
Int J Dev Biol. 1996 Feb;40(1):305-11.
During Xenopus gastrulation, the mesoderm involutes at the blastopore lip and moves on the inner surface of the BCR toward the animal pole of the embryo. Active cell migration is involved in this mesoderm translocation. In vitro, mesoderm cells migrate non-persistently and intermittently by extending and retracting multiple lamellipodia, which pull the cell body in their direction. Lamellipodia formation is induced by FN. FN fibrils are present on the BCR as part of the in vivo substrate of mesoderm migration. Mesoderm cells can attach to the BCR independently of FN, but interaction with FN is required for lamellipodia extension and cell migration on the BCR. In contrast to preinvolution mesoderm, involuted migrating mesoderm always stays on the surface of the BCR cell layer: migrating mesoderm cells do not mix with BCR cells, and a stable interface between tissues is maintained. A corresponding change in cell sorting behavior occurs during mesoderm involution. In Xenopus, the mesoderm moves as a multilayered coherent cell mass held together by cadherin-mediated cell adhesion. Aggregate formation changes mesoderm cell behavior, rendering it more continuous, persistent and directional, i.e. more efficient. The mesoderm possesses an intrinsic tissue polarity which biases the direction of its movement. In addition, the fibrillar FN matrix of the BCR contains guidance cues which also direct the mesoderm toward the animal pole. Haptotaxis is most likely not involved in this substrate-dependent guidance of the mesoderm, but intact FN fibrils seem to be required. A polarity of the BCR cell layer which underlies this anisotropy of the BCR matrix develops under the influence of the marginal zone in the late blastula. Although in other amphibian species, gastrulation depends critically on mesoderm cell migration, in Xenopus, convergent extension of the axial mesoderm seems to provide the main driving force for gastrulation.
在非洲爪蟾原肠胚形成过程中，中胚层在胚孔唇内卷，并在胚体腔顶（BCR）的内表面朝着胚胎的动物极移动。主动细胞迁移参与了这种中胚层的移位。在体外，中胚层细胞通过伸展和回缩多个片状伪足进行非持续性和间歇性迁移，这些伪足将细胞体拉向它们的方向。片状伪足的形成由纤连蛋白（FN）诱导。FN纤维作为中胚层迁移的体内底物的一部分存在于BCR上。中胚层细胞可以独立于FN附着在BCR上，但片状伪足的伸展和细胞在BCR上的迁移需要与FN相互作用。与内卷前的中胚层不同，内卷迁移的中胚层总是停留在BCR细胞层的表面：迁移的中胚层细胞不与BCR细胞混合，并且组织之间维持着稳定的界面。在中胚层内卷过程中，细胞分选行为会发生相应变化。在非洲爪蟾中，中胚层作为由钙黏蛋白介导的细胞黏附维系在一起的多层连贯细胞团移动。聚集体的形成改变了中胚层细胞的行为，使其更具连续性、持续性和方向性，即更高效。中胚层具有内在的组织极性，这使它的移动方向产生偏向。此外，BCR的纤维状FN基质包含引导线索，这些线索也将中胚层导向动物极。趋触性很可能不参与这种依赖底物的中胚层引导，但完整的FN纤维似乎是必需的。BCR基质这种各向异性所基于的BCR细胞层极性是在囊胚晚期边缘区的影响下形成的。尽管在其他两栖类物种中，原肠胚形成严重依赖中胚层细胞迁移，但在非洲爪蟾中，轴向中胚层的汇聚延伸似乎为原肠胚形成提供了主要驱动力。
