1. Friedrich Miecher Institute, P.O. Box 2543, CH-4002 Basel, Switzerland
2. Institute für Biologie II, Zellbiologie, Universität Freiburg, D-79104 Freiburg, Germany
3. University Women’s Clinic, Biochemistry/Endocrinology Unit, Department of Research, Schanzenstrasse 46, CH-4031 Basel, Switzerland