1. Cell Biology and Biophysics Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
2. Developmental Biology Unit, EMBL, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
3. Institute of Zoology, Department for Developmental Physiology, University of Heidelberg, INF 230, D-69120 Heidelberg, Germany.
4. Institute of Toxicology and Genetics, Karlsruhe Institute of Technology (KIT), Post Office Box 3640, D-76021 Karlsruhe, Germany.