1. G. Ferrari, E. Paolucci, A. Stornaiuolo, F. Mavilio, H. San Raffaele–Telethon Institute for Gene Therapy (TIGET), 20132 Milan, Italy.
2. G. Cusella–De Angelis, Istituto di Anatomia Umana Normale, University of Pavia, 27100 Pavia, Italy.
3. M. Coletta and G. Cossu, Dipartimento di Istologia ed Embriologia Medica, University of Rome La Sapienza, 00161 Rome, Italy.