A cell undergoing apoptosis displays transmembrane signals that may be recognized by another cell. The cell that recognizes the transmembrane signals begins to express the CED protein family. CED-2, CED-5 and CED-12 interact in a trimeric Guanine Nucleotide Exchange Factor (GEF), and activate CED-10, a Rac-GTPase. CED-10 then directly influences the polymerization of the actin cytoskeleton, promoting the phagocytic activity of the engulfing cell.