1. Unit of Anatomy; Department of Medicine; University of Fribourg; Route de Gockel, 1 Fribourg Switzerland
2. International Centre for Genetic Engineering and Biotechnology; Trieste Italy
3. Max F. Perutz Laboratories; Vienna Bio Center; Department of Medical Biochemistry; Medical University of Vienna; Vienna Austria
4. Unit of Anatomy; Department of Medicine; University of Bern; Bern Switzerland