ROLE OF NCAM, CADHERINS, AND MICROFILAMENTS IN CELL-CELL CONTACT FORMATION IN TM4 IMMATURE MOUSE SERTOLI CELLS

To determine events that lead to the formation of intercellular contac ts, we examined the spatial and temporal distribution of NCAM, cadheri ns, and F-actin in TM4 cells by immunofluorescence and laser scanning confocal microscopy. TM4 cells exhibited epithelioid characteristics a nd formed large overlapping lamella-like cell-cell contacts that conta ined a high concentration of NCAM. NCAM-rich lamellae formed from smal ler NCAM patches at the ends of filopodia-like contacts between adjace nt cells. Cadherins, as visualized by a pan-cadherin antibody, were pr esent in a pattern distinctly different from that of NCAM. Although in filopodia-like contacts, both cadherins and NCAM were often concentra ted at filopodial tips, in the larger lamella-like contacts that devel oped later, cadherins were located in an irregular punctate pattern on ly at the distal and more apical margins of the slanted NCAM-rich cont act regions. Patterns of NCAM and microfilament (MF) bundle distributi on were distinctly different, suggesting that the ends of these MF bun dles were not physically linked to NCAM. By contrast, cadherins were c oncentrated at the ends of MF bundles at all stages of contact formati on examined. Interestingly, this association of cadherins with MF bund les was mostly seen at the edge of the overlapping processes. In the l ower cell process, MF bundles at the contact site were often arranged in random fashion, indicating an asymmetric distribution of MF in the junctional region. However, N-cadherin was enriched only at sites wher e MF bundles from both the upper and lower cell processes were aligned and terminated at the junctional membrane. Thus the organization of t he actin cytoskeleton at cell-cell contact sites is influenced by the differential localization of different cadherins. These data also sugg est that different mechanisms are involved in the accumulation of NCAM and cadherins in cell-cell contact regions. (C) 1997 Wiley-Liss, Inc.