title: Cell-cell interactions in early embryogenesis: a molecular approach to the role of calcium.
abstract: Compaction, a process of cell-cell adhesion between mouse blastomeres or between embryonal carcinoma (EC) cells requires calcium ions. A decompaction effect similar to that observed in the absence of Ca2+ is triggered by Fab fragments of rabbit anti-EC IgG. This effect occurs through the recognition of a specific cell-surface glycoprotein named uvomorulin. An 84,000 dalton fragment of uvomorulin (UMt) has been previously extracted by trypsin from EC cell membranes and purified. WE present evidence that effects of Ca2+ on compaction are transmitted through conformational changes in uvomorulin. First, Ca2+ protects UMt from further proteolysis by trypsin. Mn2+ and Sr2+ have similar effects, whereas this protection is reversed by La3+. Second, UMt can bind the monoclonal antibody De1 only in the presence of Ca2+ (half-binding at 10(-5) M Ca2+). This antigenic exposure also takes place in the presence of Mn2+ or Sr2+ and is reversed by La3+. Third, metal ions (Ca2+, Mn2+, Sr2+) that promote trypsin resistance and recognition by DE1 are found to trigger the compaction of morulae and EC cells. Metal ions (La3+) that reduce trypsin resistance and affinity for DE1 result in decompaction.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D015820:Cadherins; D002118:Calcium / Q000037:antagonists & inhibitors / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000502:physiology; D002448:Cell Adhesion; D006023:Glycoproteins / Q000502:physiology*; D051379:Mice; D008970:Molecular Weight; D011485:Protein Binding; D011487:Protein Conformation; D013724:Teratoma / Q000473:pathology*; D014357:Trypsin / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D015820:Cadherins; D002135:Calcium-Binding Proteins; D006023:Glycoproteins; D014357:Trypsin; D002118:Calcium