1. Department of Medical Cell Biology, Biomedicum, University of Uppsala, Box 571, S-751 23 Uppsala, Sweden
2. Department of Endocrinology, Karolinska Institute, Karolinska Hospital, Box 60500, S-104 01 Stockholm, Sweden
3. Institute for Radiation Science, Department of Physical Biology, University of Uppsala, Box 535, S-75121 Uppsala, Sweden
4. Department of Histology and Cell Biology, University of Umeå, S-901 87 Umeå, Sweden