Kanazawa Y, Doi Y, Furukawa H, Kayashima K, Fujimoto S
Department of Orthopedic Surgery, University of Occupational and Environmental Health, Kitakyushu, Japan.
Arch Histol Cytol. 1996 Oct;59(4):317-30. doi: 10.1679/aohc.59.317.
Rat hind limb buds, aged between prenatal days 14 and 18, were used for electron microscopy and immunocytochemistry of fibronectin, laminin and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining indicative of DNA fragmentation. Fibronectin and laminin were actively synthesized in the rough endoplasmic reticulum of epidermal cells in the apical ectodermal ridge between prenatal days 14 and 15, but most cells underwent apoptosis after prenatal day 15. As the regression of the apical ectodermal ridge progressed, mesenchymal cells associated with the marginal veins were successively incorporated into the endothelium devoid of the basal lamina. No mitotic figures of endothelial cells were recognized either in the marginal vein or in the surrounding growing capillaries. Extracellular matrix components connected the adjacent mesenchymal cells, with the endothelium of such vessels immunoreacting to fibronectin and laminin. In addition, fibronectin-immunoreactive networks among the interstices of the mesenchymal cell cords developed in the avascular zone between the epidermis and the growing capillaries at prenatal day 15, but became inconspicuous at prenatal day 16. These results indicate that the apoptosis of the epidermal cells is the major reason for the regression of the apical ectodermal ridge, and that the capillary ingrowth from the marginal veins to the avascular zone is accelerated by transformation of mesenchymal cells to endothelial ones. Fibronectin and laminin seem to play crucial roles in capillary growth, especially in the adhesion between endothelial cells of the pre-existing vessels and mesenchymal cells.
采用孕14至18天的大鼠后肢芽进行电子显微镜检查以及纤连蛋白、层粘连蛋白和末端脱氧核苷酸转移酶介导的dUTP生物素缺口末端标记染色（指示DNA片段化）的免疫细胞化学分析。在孕14至15天期间，顶端外胚层嵴的表皮细胞粗面内质网中积极合成纤连蛋白和层粘连蛋白，但在孕15天后大多数细胞发生凋亡。随着顶端外胚层嵴的退化进展，与边缘静脉相关的间充质细胞相继并入无基膜的内皮。在边缘静脉或周围生长的毛细血管中均未识别到内皮细胞的有丝分裂象。细胞外基质成分连接相邻的间充质细胞，此类血管的内皮对纤连蛋白和层粘连蛋白呈免疫反应。此外，在孕15天表皮与生长中的毛细血管之间的无血管区，间充质细胞索间隙中形成了纤连蛋白免疫反应网络，但在孕16天时变得不明显。这些结果表明，表皮细胞凋亡是顶端外胚层嵴退化的主要原因，并且间充质细胞向内皮细胞的转化加速了从边缘静脉向无血管区的毛细血管向内生长。纤连蛋白和层粘连蛋白似乎在毛细血管生长中起关键作用，尤其是在既有血管的内皮细胞与间充质细胞之间的黏附中。
