National Institute of Health Sciences
1-18-1 Kami-Yoga, Setagaya-ku,Tokyo 158
 The Tokyo Metropolitan Institute of Medical Science
3-18-22 Hon-Komagome, Bunkyo-ku, Tokyo 113
Each cell in a multicellular animal is programmed during development to respond to specific outer chemical signals. Some of these chemical signals activate receptor proteins on the surface of the cell that trigger series of membrane and intracellular signal transductions, and eventually influence gene expressions. These complex cell signaling mechanisms have been unveiled at molecular levels in various multicellular organisms in the past decade. It was found that these molecular signaling pathways or what we may call cell signaling networks (CSN) play important roles in wide range of biological phenomena that characterize multicellular animals. These phenomena include development, differentiation, reproduction, morphogenesis, carcinogenesis, apoptosis, and even learning.