GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED CELL-SURFACE PROTEINS REGULATE POSITION-SPECIFIC CELL AFFINITY IN THE LIMB BUD

Although regional differences in mesenchymal cell affinity in the limb bud represent positional identity, the molecular basis for cell affin ity is poorly understood. We found that treatment of the cell surface with bacterial phosphatidylinositol-specific phospholipase C (PI-PLC) could change cell affinity in culture. When PI-PLC, was added to the c ulture medium, segregation of the progress zone (PZ) cells from differ ent stage limb buds was inhibited. Similarly, sorting out of the cells from different positions along the proximodistal (PD) axis of the sam e stage limb buds was disturbed. Since PI-PLC: can remove glycosylphos phatidplinositol (GPI)-anchored membrane bound proteins from the cell surface, the GPI-anchored cell surface proteins may be involved in sor ting out. To define the GPI-anchored molecules that determine the segr egation of limb mesenchymal cells, we examined the effect of neutraliz ing antibody on the EphA4 receptor that binds to GPI-anchored cell sur face ligands, called ephrin-A. Sorting out of the PZ cells at differen t stages could be inhibited by the neutralizing antibody to EphA4, The se results suggest that EphA4 and its GPI-anchored ligands are, at lea st in part, involved in sorting out of limb mesenchymal cells with dif ferent proximal-distal positional values, and that GPI-anchored cell s urface proteins play important roles in determining cell affinity in t he limb bud. (C) 1998 Academic Press.