1. Stem Cell Research Institute, San Raffaele Hospital, 20132 Milan, Italy
2. Department of Experimental Medicine, Human Anatomy Institute, University of Pavia, 27100 Pavia, Italy
3. Department of Experimental, Environmental Medicine, and Medical Biotechnology, University of Milano-Bicocca, 20126 Milan, Italy
4. Stem Cell Laboratory, Department of Neurological Science,
5. Department of Pathology, Division of General Pathology, University of Verona, 37129 Verona, Italy
6. Department of Biology, University of Milan, 20122 Milan, Italy