1. Department of Anatomy and Embryology, Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai,Tsukuba, Ibaraki 305-8575, Japan.
2. Department of Pathology and Immunology, Washington University, School of Medicine, 660 S. Euclid Ave. Box 8118, St Louis, MO 63110, USA.
3. Laboratory for Stem Cell Biology, RIKEN Center for Developmental Biology, Minatojima-minamimachi 2-2-3, Chu-o-ku, Kobe, Hyogo, 650-0047, Japan.
4. Department of Molecular and Developmental Biology, Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai,Tsukuba, Ibaraki 305-8575, Japan.
5. PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan.