1. Department of Medicine and Division of Rheumatology, Immunology and Allergy, Brigham and Women's Hospital, Harvard Medical School, 1 Jimmy Fund Way, Boston, MA 02115, USA.
2. Department of Cell and Developmental Biology, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Yoshida-honmachi, Kyoto 606-8501, Japan.
3. RIKEN Center for Developmental Biology, Minatojima-Minamimachi, Chuo-ku, Kobe 650-0047, Japan.