The glomerular slit diaphragm is a modified adherens junction

The glomerular slit diaphragm between podocyte foot processes shares typica l morphologic features with an adherens junction. Differentiated cultured p odocytes form cellular structures comparable to filtration slits in vivo. A t those sites, zonula occludens-1 (ZO-1) was coexpressed with P-cadherin as well as with alpha-, beta-, and gamma-catenin. In situ, P-cadherin was det ected at the slit diaphragm in association with ZO-1 as shown by confocal m icroscopy and immunogold double labeling electron microscopy. P-cadherin ex pression in vivo and in vitro was confirmed by reverse transcription-PCR. T hese findings led to the concept that the slit diaphragm represents an adhe rens junction composed of P-cadherin, alpha-, beta-, and gamma-catenin, and ZO-1. In contrast to an adherens junction of a similar composition recentl y described in cultured fibroblasts, the slit diaphragm complex does not co ntain vinculin, which was found in nearby focal contacts. A P-cadherin-base d adherens junction is well-suited to explain the zipper-like structure of the slit diaphragm. The present study should allow new avenues leading to t he identification of additional slit diaphragm-associated proteins conferri ng specificity to this unique cell junction.