Cell to Cell Adhesion Systems in Xenopus laevis, the South African Clawed Frog I. Detection of Ca2+ Dependent and Independent Adhesion Systems in Adult and Embryonic Cells

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Abstract
The reaggregation kinetics of frog (Xenopus laevis) cells prepared using several different dissociation procedures were monitored. Two distinct modes of cell adhesion were revealed, one mediated by Ca2+ dependent cell-cell adhesion system (CDS) and the other mediated by Ca2+ independent one (CIDS). CDS was detected in frog embryonic (two-cell stage to neurula) cells and in cells of epithelial cell lines (A6 and A8), while CIDS was detected only in A6 cells. Frog CDS was resistant to 0.01% tryptic digestion in the presence of 1 mM Ca2+ and CIDS was resistant to dilute (0.0001%) tryptic digestion. Cells with both mechanisms were prepared by dissociation with 1 mM EDTA and both mechanisms were absent in cells dissociated with 0.01% trypsin and 1 mM EDTA. Frog CDS and CIDS functioned in a temperature dependent and independent manner, respectively. Properties of frog CDS and CIDS revealed in this study were the same as those of mammalian or avian CDS and CIDS, respectively. Frog cells with CDS cross-adhered to mammalian epithelial (F9) cells but not to fibroblastic (V79) cells Ca2+ dependently. Monoclonal antibody ECCD-1 raised against mouse epithelial CDS blocked aggregation of frog A8 cells. These results suggest the similarity between frog CDS and mammalian epithelial type CDS.