We gratefully acknowledge past and/or current support by the German Research Foundation (http://www.dfg.de/ ), the National Institute of Health (NIH, http://www.nih.gov/ ), the National Science Foundation (NSF, http://www.nsf.gov/ ) and the Natural and Medical Sciences Research Center of the University Medicine Mainz (Naturwissenschaftlich-medizinisches Forschungszentrum, NMFZ)