1. Molecular and Cancer Biology Program, Haartman Institute and Biomedicum Helsinki, Post Office Box 63, University of Helsinki, Helsinki 00014, Finland.
2. Department of Anatomy and Cell Biology, University of Bergen N-5009 Bergen, Norway.
3. Helsinki University Central Hospital Laboratory Diagnostics, Post Office Box 401, Helsinki 00029 HYKS, Finland.
4. Center for Developmental Biology, University of Texas Southwestern Medical Center, Dallas, TX 75235–9133, USA.