Fig. 1

The cellular events of N signaling pathway. The steps are (1) N and Dl proteins are transcribed, translated and transported to the cell membrane; (2) Dl undergoes an endocytic processing step to become the ligand for N; (3) the Dl ligand and N receptor interact resulting in a cleavage and endocytosis of a N fragment; (4) A second cleavage releases a N product that is translocated to the nucleus