1. Signal Transduction Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
2. Reproductive & Developmental Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
3. Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, Missouri, USA
4. Shriners Hospitals for Children, St. Louis, Missouri, USA
5. MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
6. Departments of Medicine and Biochemistry, Duke University Medical Center, Durham, North Carolina, USA