CLAUDINS AND OCCLUDIN : COMPARISON WITH CONNEXIN

在紧密连接(TJ)中，TJ链与相邻细胞的TJ链横向相连，形成成对的链，从而消除细胞外空间。Claudin-1和Claudin-2是TJ的完整膜蛋白，导入L成纤维细胞后，可重组成对的TJ链。Claudins组成一个多基因家族，两个以上不同的Claudins在单个细胞中共表达，这引发了这样的问题：异源Claudins是否形成异构体TJ链，以及Claudins是否以异嗜性的方式在每对链之间相互作用。为了回答这些问题，我们将claudin-1、-2和-3中的两个共转染到L细胞中，并检测到它们在细胞-细胞边界的共浓度作为精细的网络。免疫复制电子显微镜证实，不同的Claudins共结合到单个TJ链中。接下来，将两个单独表达claudin-1、-2和-3的L转染体进行共培养，我们发现claudin-3链与claudin-1和claudin-2链横向结合形成成对的链，而claudin-1链不与claudin-2链相互作用。我们的结论是，除某些组合外，不同种类的克拉丁可以在TJ链内和TJ链之间相互作用。这种Claudins的组装方式可以增加TJ链的结构和功能的多样性。

In tight junctions (TJs), TJ strands are associated laterally with those of adjacent cells to form paired strands to eliminate the extracellular space. Claudin-1 and-2, integral membrane proteins of TJs, reconstitute paired TJ strands when transfected into L fibroblasts. Claudins comprise a multigene family and more than two distinct claudins are co-exrressed in single cells, raising the questions of whether heteroseneous claudins form heteromeric TJ strands and whether claudins interact between each of the paired strands in a heterophilic manner. To answer these questions, we co-transfected two of claudin-1, -2 and -3 into L cells, and detected their coconcentration at cell-cell borders as elaborate networks. Immunoreplica electron microscopy confirmed that distinct claudins were co-incorporated into individual TJ strands. Next, two L transfectants singly expressing claudin-1, -2 or -3 were cocultured, and we found that claudin-3-strands laterally associated with claudin-1 and claudin-2 stranas to form paired strands, whereas claudin-1 strands did not interact with claudin-2 strands. We concluded that distinct species of claudins can interact within and between TJ strands except in some combinations. This mode of assembly of claudins could increase the diversity of the structure and functions of TJ strands.