1. Wellcome Trust Centre for CellMatrix Research, Faculty of Life Sciences, The University of Manchester, Manchester M13 9PT, UK
2. Present address: Institute of Genetic Medicine, Newcastle University, International Centre for Life, Newcastle upon Tyne NE1 3BZ, UK
3. Center for Biochemistry, University of Cologne, D50931 Cologne, Germany
4. Center for Molecular Medicine, University of Cologne, D50931 Cologne, Germany
5. Institute for Dental Research and Musculoskeletal Biology, Medical Faculty, University of Cologne, D50931 Cologne, Germany