1. Division of Mammalian Development, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka 411-8540, Japan
2. Department of Genetics, The Graduate University for Advanced Studies, Mishima, Shizuoka 411-8540, Japan
3. Department of Kidney Development, Institute of Molecular Embryology and Genetics (IMEG), Kumamoto University, Kumamoto 860-061, Japan
4. Department of Developmental Biology and Division of Dermatology, Washington University School of Medicine, Box 8103, 660 South Euclid Avenue, St Louis, MO 63110-1095, USA