1. H. Z. Sheng, T. Yamashita, H. Westphal, Laboratory of Mammalian Genes and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
2. K. Moriyama, Department of Anatomy, Shimane Medical University, 89-1 Enya Izumo 693, Japan.
3. H. Li, Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan.
4. S. S. Potter, Division of Developmental Biology, Children's Hospital Research Foundation and Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA.
5. K. A. Mahon, Department of Cell Biology, Baylor College of Medicine, Houston, TX 77030, USA.