[1] RIKEN, Ctr Dev Biol, Chuo Ku, Kobe, Hyogo 6500047, Japan
[2] Natl Inst Genet, Mishima, Shizuoka 411, Japan
[3] Grad Univ Adv Studies, Dept Genet, Mishima, Shizuoka, Japan
[4] Natl Inst Basic Biol, Okazaki, Aichi 444, Japan
[5] Tokyo Metropolitan Univ, Dept Biol, Tokyo 158, Japan
[6] Tohoku Univ, Inst Dev Aging & Canc, Dept Dev Neurobiol, Aoba Ku, Sendai, Miyagi, Japan
[7] Okayama Univ, Grad Sch Nat Sci & Technol, Okayama, Japan
[8] Kyushu Univ, Grad Sch Sci, Dept Biol, Fukuoka 812, Japan
[9] Mitsubishi Kagaku Inst Life Sci, Tokyo, Japan
[10] Kyoto Univ, Inst Virus Res, Mol Genet Lab, Kyoto 606, Japan
[11] MIT, Ctr Learning & Memory, Cambridge, MA 02139 USA