Amerongen H M, Mack J A, Wilson J M, Neutra M R
Department of Anatomy and Cellular Biology, Harvard Medical School, Boston, Massachusetts 02115.
J Cell Biol. 1989 Nov;109(5):2129-38. doi: 10.1083/jcb.109.5.2129.
The organization of the basolateral membrane domain of highly polarized intestinal absorptive cells was studied in adult rat intestinal mucosa, during development of polarity in fetal intestine, and in isolated epithelial sheets. Semi-thin frozen sections of these tissues were stained with a monoclonal antibody (mAb 4C4) directed against Na+,K+-ATPase, and with other reagents to visualize distributions of the membrane skeleton (fodrin), an epithelial cell adhesion molecule (uvomorulin), an apical membrane enzyme (aminopeptidase), and filamentous actin. In intact adult epithelium, Na+,K+-ATPase, membrane-associated fodrin, and uvomorulin were concentrated in the lateral, but not basal, subdomain. In the stratified epithelium of fetal intestine, both fodrin and uvomorulin were localized in areas of cell-cell contact at 16 and 17 d gestation, a stage when Na+,K+-ATPase was not yet expressed. These molecules were excluded from apical domains and from cell surfaces in contact with basal lamina. When Na+,K+-ATPase appeared at 18-19 d, it was codistributed with fodrin. Detachment of epithelial sheets from adult intestinal mucosa did not disrupt intercellular junctions or lateral cell contacts, but cytoplasmic blebs appeared at basal cell surfaces, and a diffuse pool of fodrin and actin accumulated in them. At the same time, Na+,K+-ATPase moved into the basal membrane subdomain, and extensive endocytosis of basolateral membrane, including Na+,K+-ATPase, occurred. Endocytosis of uvomorulin was not detected and no fodrin was associated with endocytic vesicles. Uvomorulin, along with some membrane-associated fodrin and some Na+,K+-ATPase, remained in the lateral membrane as long as intercellular contacts were maintained. Thus, in this polarized epithelium, interaction of lateral cell-cell adhesion molecules as well as basal cell-substrate interactions are required for maintaining the stability of the lateral membrane skeleton and the position of resident membrane proteins concentrated in the lateral membrane domain.
在成年大鼠肠黏膜、胎儿肠道极性发育过程以及分离的上皮片中，研究了高度极化的肠吸收细胞基底外侧膜结构域的组织情况。这些组织的半薄冰冻切片用针对Na⁺,K⁺-ATP酶的单克隆抗体（mAb 4C4）以及其他试剂染色，以观察膜骨架（血影蛋白）、上皮细胞黏附分子（桥粒芯糖蛋白）、顶端膜酶（氨肽酶）和丝状肌动蛋白的分布。在完整的成年上皮中，Na⁺,K⁺-ATP酶、膜相关血影蛋白和桥粒芯糖蛋白集中在外侧而非基底亚结构域。在胎儿肠道的复层上皮中，在妊娠16和17天时，血影蛋白和桥粒芯糖蛋白都定位在细胞间接触区域，此时Na⁺,K⁺-ATP酶尚未表达。这些分子被排除在顶端结构域以及与基膜接触的细胞表面之外。当Na⁺,K⁺-ATP酶在18 - 19天时出现时，它与血影蛋白共分布。从成年肠黏膜分离上皮片不会破坏细胞间连接或细胞外侧接触，但在基底细胞表面会出现细胞质泡，并且血影蛋白和肌动蛋白的弥散池在其中积累。与此同时，Na⁺,K⁺-ATP酶移入基底膜亚结构域，并且发生包括Na⁺,K⁺-ATP酶在内的基底外侧膜的广泛内吞作用。未检测到桥粒芯糖蛋白的内吞作用，并且没有血影蛋白与内吞小泡相关。只要细胞间接触得以维持，桥粒芯糖蛋白以及一些膜相关血影蛋白和一些Na⁺,K⁺-ATP酶就会保留在外侧膜中。因此，在这种极化上皮中，细胞外侧细胞间黏附分子的相互作用以及基底细胞与底物的相互作用对于维持外侧膜骨架的稳定性以及集中在外侧膜结构域的驻留膜蛋白的位置是必需的。
