Van Hoof J, Harrisson F, Andries L, Vakaet L
Differentiation. 1986;31(1):14-9. doi: 10.1111/j.1432-0436.1986.tb00377.x.
The relationship between the presence of glycosaminoglycans (GAGs) and the morphology of the middle layer or mesoblast was examined by performing transmission electron microscopy of chicken blastoderms microinjected with GAG-degrading enzymes. The controls included microinjections with saline or trypsin, as well as solid-phase assays for proteolytic activity in commercially available GAG-degrading preparations. The results indicate that, in normal as well as in saline-injected blastoderms, middle-layer cells are rounded or cuboidal in shape, and are linked to each other by small intercellular junctions in the primitive-streak region. As they migrate laterally along the basal lamina, they appear as typical mesenchymal cells, being separated by large intercellular spaces and covered by cell processes. The removal of hyaluronate (by the microinjection of hyaluronidases) led to compaction of the middle-layer cells in the area lateral to the primitive streak. These cells lost their mesenchymal aspect and retracted their processes, and intercellular junctions were observed. The presence of proteolytic activity in the enzyme preparations did not interfere with the results. On the basis of the results obtained using this microinjection technique, we were able to confirm at the ultrastructural level that hyaluronate, due to its space-creating properties, promotes the detachment of ingressed primitive-streak cells and preserves the mesenchymal aspect of the middle layer during the lateral migration of single cells along the basal lamina. Whether the presence of hyaluronate is necessary to allow positioning of the mesoblast could not be inferred using our experimental procedure. We present evidence that this molecule, as well as having physicochemical properties, is also involved in the modulation of tissue interactions during gastrulation.
通过对注射了糖胺聚糖（GAG）降解酶的鸡胚盘进行透射电子显微镜检查，研究了GAG的存在与中层或中胚层形态之间的关系。对照组包括注射生理盐水或胰蛋白酶，以及对市售GAG降解制剂中的蛋白水解活性进行固相分析。结果表明，在正常以及注射生理盐水的胚盘中，中层细胞呈圆形或立方形，在原条区域通过小的细胞间连接相互连接。当它们沿着基膜横向迁移时，它们呈现为典型的间充质细胞，被大的细胞间隙分隔并被细胞突起覆盖。去除透明质酸（通过显微注射透明质酸酶）导致原条侧面区域的中层细胞致密化。这些细胞失去了间充质形态并缩回了它们的突起，并且观察到了细胞间连接。酶制剂中蛋白水解活性的存在并不干扰结果。基于使用这种显微注射技术获得的结果，我们能够在超微结构水平上证实，由于其创造空间的特性，透明质酸促进了内陷的原条细胞的脱离，并在单个细胞沿着基膜横向迁移期间保持了中层的间充质形态。使用我们的实验程序无法推断透明质酸的存在是否是中胚层定位所必需的。我们提供的证据表明，这种分子除了具有物理化学性质外，还参与了原肠胚形成过程中组织相互作用的调节。
