Multicellular organisms regulate various physiological functions by exchanging information between cells. While the information or stimulation transmitted by hormones and neurotransmitters can result in various responses (proliferation, differentiation, modulation of cellular functions) via cell surface receptors, many intracellular proteins are also known to play important roles in the process. We are attempting to elucidate the network of signaling molecules involved in the pathogenesis of diseases such as obesity and diabetes by using genetic engineering techniques and thus contribute to the development of new therapeutic agents for these diseases.