1. Department of Anatomy and Molecular Embryology; Ruhr-University; Bochum Germany
2. Cell Biology Group; Institute of Zoology; Technical University of Braunschweig; Germany
3. Institute of Biochemistry; University of Erlangen; Erlangen Germany
4. Department of Cytology; Ruhr-University; Bochum Germany
5. Maurice E. Müller Institute for Structural Biology, Biocenter; Basel Switzerland
6. MRC Laboratory of Molecular Biology and Trinity College; Cambridge United Kingdom
7. Department of Physical Biochemistry; Max-Planck-Institute of Molecular Physiology; Dortmund Germany