The claudin family : Its involvement in interecellular sealing and epithelial polarity

(1)紧密连接（tight junction， TJ）及其粘附分子cladin负责单层上皮的屏障功能，但TJ在包括表皮在内的哺乳动物分层上皮的屏障功能中并未发挥重要作用。在这项研究中，我们培育了claudin-1缺陷小鼠，发现这些小鼠在出生后一天内死亡，皮肤起皱。脱水试验和经皮失水测量显示，这些小鼠的表皮屏障受到严重影响，尽管角质形成细胞的层状组织似乎正常。这些意想不到的发现促使我们重新研究野生型小鼠表皮中的TJs。免疫荧光显微镜用抗闭塞蛋白单抗（一种tj特异性标记物）仔细检查，发现颗粒层中有连续的tj，其中claudin-1和-4集中。在claudin-1缺失的小鼠中，claudin-1似乎只是从这些TJs中被移除，留下了闭塞的TJs。有趣的是，在野生型表皮中，这些occludin阳性的TJs有效地阻止了皮下注射示踪剂（~ 600道顿）向皮肤表面的扩散，而在claudin-1缺失的表皮中，示踪剂似乎可以通过这些TJs。这些发现提供了第一个证据，表明持续的基于cladin的TJs发生在表皮中，这些TJs对哺乳动物皮肤的屏障功能至关重要。(2)紧密结（TJ）是一种线性聚合物，是质膜内典型的蛋白性聚合物，其物理化学性质尚不清楚。最近，claudin被确定为TJ链的主要成分，并且在小鼠L成纤维细胞中外源表达时，它们被证明在细胞-细胞边界重建TJ链。在本研究中，我们发现GFP（绿色荧光蛋白）与claudin-1融合蛋白也可以重建L成纤维细胞中的TJ链，使我们能够直接观察活细胞中的单个TJ链。少

(1) The tight junction (TJ) and its adhesion molecules, claudins, are responsible for the barrier function of simple epithelia, but TJs have not been thought to play an important role in the barrier function of mammalian stratified epithelia including the epidermis. In this study, we generated claudin-1-deficient mice and found that the animals died within one day of birth with wrinkled skin. Dehydration assay as well as transepidermal water loss measurements revealed that in these mice the epidermal barrier was severely affected, although the layered organization of keratinocytes appeared to be normal. These unexpected findings prompted us to re-examine TJs in the epidermis of wild-type mice. Close inspection by immunofluorescence microscopy with an anti-occludin mAb, a Tjspecific marker, identified continuous TJs in the stratum granulosum, where claudin-1 and -4 were concentrated. In claudin-1-deficient mice, claudin-1 appeared to have simply been removed from these TJs leaving occlu … More din(and also claudin-4)-positive TJs. Interestingly, in the wild-type epidermis, these occludin-positive TJs efficiently prevented the diffusion of subcutaneously-injected tracer (〜600 dalton) toward the skin surface, whereas in the claudin-1-deficient epidermis, the tracer appeared to pass through these TJs. These findings provide the first evidence that continuous claudin-based TJs occur in the epidermis, and that these TJs are crusial for the barrier function of the mammalian skin.(2) The tight junction (TJ) stand is linear polymer, typical of proteinaceous polymers within plasma membranes, the physicochemical nature of which remains elusive. Recently, claudins were identified as major constituents of TJ strands, and they were shown to reconstitute TJ strands at cell-cell borders when exogenously expressed in mouse L fibroblasts. In this study, we show that the GFP (green fluorescent protein) fusion protein with claudin-1 can also reconstitute TJ strands in L fibroblasts, allowing us to directly observe individual TJ strands in live cells. Less