Department of Molecular Biology, Max Planck Institute for Developmental Biology, University of Tübingen, Sand 14, 72076 Tübingen, Germany.|Department of Molecular Biology, Max Planck Institute for Developmental Biology, University of Tübingen, Sand 14, 72076 Tübingen, Germany.|Department of Molecular Biology, Max Planck Institute for Developmental Biology, University of Tübingen, Sand 14, 72076 Tübingen, Germany.|Department of Molecular Biology, Max Planck Institute for Developmental Biology, University of Tübingen, Sand 14, 72076 Tübingen, Germany.|Department of Molecular Biology, Max Planck Institute for Developmental Biology, University of Tübingen, Sand 14, 72076 Tübingen, Germany.