An endogenous lectin found in rat astrocyte cultures has a role in cell adhesion but not in cell proliferation

The presence of an endogenous cerebellar soluble lectin (CSL) has been demonstrated in cultured rat astrocytes by using immunocytochemical techniques. In these cells, the location of lectin CSL was found intracellularly as well as on the external surface of the plasma membrane of the cell bodies and processes, especially in the zones of contact between cells. This suggested that CSL could have a role in adhesion of astrocytes to sister cells. Kinetics of adhesion of astrocytes to culture dishes precoated with CSL showed a rapid binding of these cells. In confluent astrocyte cultures, anti-CSL Fab fragments affected the shape and organization of astrocytes (retraction of the cytoplasm), but they did not detach cells from the substratum. These results indicated that CSL has adhesive properties for astroglial cells and is probably involved 1) in adhesion of astrocytes to sister cells; 2) in binding of protoplasmic regions of astrocyte membrane to the substratum. Further support for these roles came from demonstration of the presence in cultures of glycoprotein ligands recognized by this lectin. The problem of the mitogenic properties of the lectin was also questioned. The addition of CSL to confluent astroglial cultures was able to stimulate only by 40% the proliferation of these cells at an optimal concentration of 5 micrograms CSL lectin/ml of culture medium. This indicated that CSL is not a powerful growth factor for astrocytes.