We are indebted to the Functional Genomics Center Zurich (Zurich, CH) for financial as well as technical support (thanks especially to Andrea Patrignani, Dr Ulrich Wagner, and Dr Hubert Rehrauer for their assistance in data generation and evaluation), and to Dr Michael Leviten (San Carlos, CA) for the help in generating Mtf1 conditional knockout mice. We also thank Prof. Ueli Schibler (Geneva, CH) for his advice on the ADDER technique, Prof. Michel Aguet (Epalinges-Lausanne, CH) for the gift of Mx-Cre mice, Dr George Hausmann and Dr Michael Fetchko for critical reading of the manuscript, and Fritz Ochsenbein for preparing the figures. Funding to pay the Open Access publication charges for this article was provided by the Kanton Zurich.