1 Department of Genetics & Cell Biology, Faculty of Health, Medicine & Life Sciences, Maastricht University, P.O. Box 616, 6200 MD Maastricht, the Netherlands. Electronic address: glatz@maastrichtuniversity.nl.
2 National Institute of Applied Sciences (INSA)-Lyon, University of Lyon, Inserm UMR 1060, Inra UMR 1397, 69100 Villeurbanne, France. Electronic address: michel.lagarde@insa-lyon.fr.