1. Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Faculty of Medicine, University of Freiburg, Freiburg D-79104, Germany
2. Faculty of Biology, University of Freiburg, Schaenzlestrasse 1, Freiburg D-79104, Germany
3. Departamento de Informática, Universidad de Oviedo, Jesús Arias de Velasco, Oviedo 33005, Spain
4. Developmental Genetics, University of Basel Medical School, Basel CH-4058, Switzerland
5. Centre for Organismal Studies, Heidelberg D-69120, Germany