1. Laboratory of Stem Cell and Neuro-Vascular Biology, Cell and Development Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health 1 , Bethesda, MD 20892 , USA
2. International Research Center for Medical Sciences, Kumamoto University 2 , Kumamoto 860-0811 , Japan
3. Cancer and Developmental Biology Laboratory, National Cancer Institute, National Institutes of Health 3 , Frederick, MD 21702 , USA
4. Cancer Science Institute of Singapore, National University of Singapore 4 , Singapore 117599
5. Department of Microscopic and Developmental Anatomy, Tokyo Women's Medical University 5 , Tokyo 162-8666 , Japan