Distinct calcium-independent and calcium-dependent adhesion systems of chicken embryo cells.

Abstract

Three criteria were used to distinguish different systems of embryonic cell adhesion: dependence on Ca2+, involvement of particular cell surface molecules and binding specificity. Characterization of the adhesion with respect to cell surface molecules was carried out by using specific antibodies against the neural and liver cell adhesion molecules (N-CAM and L-CAM) and antibodies raised against retinal cells prepared by limited trypsinization in the presence of Ca2+ (called T/Ca cells). Aggregation of cells prepared from retina or brain without Ca2+ did not require Ca2+ and was inhibited by anti-(N-CAM) antibodies but not by anti-(L-Cam) or anti-T/Ca cell antibodies. Cells obtained from the same tissues in the presence of Ca2+ did require Ca2+ to aggregate. This aggregation was inhibited by anti-T/Ca cell antibodies but not by anti-(N-CAM) or anti-(L-CAM) antibodies. Hepatocyte aggregation also required Ca2+ and was inhibited only by anti-(L-CAM) antibodies. These results define 3 antigenically distinct cell adhesion systems in the embryo and raise the possibility of additional systems. The neural Ca2+-independent system displayed a limited tissue specificity, mediating binding to neural but not liver cells. Ca2+-dependent systems of neural and liver cells caused binding to all cell types tested. Ca2+-dependent system was most active in retinal cells from 6-7 day embryos; the Ca2+-independent system was most active at later times during development. Treatments that inhibited the Ca2+-independent or Ca2+-dependent systems had very different effects on the fasciculation of neurites from dorsal root ganglia. Apparently, Ca2+-independent and Ca2+-dependent adhesion systems play different functional roles during embryogenesis.