We thank Herbert JaÈckle for his encouragement and support, Aki Shima for communicating his mutagenesis protocol, Detlev Arendt, Carola Burgtorf, Clemens Grabher and Sylke Winkler for critical comments on the manuscript,Erika Grzebysz, Werner Fink and Uschi Jahns-Meyer for expert maintenance of the fish facilities.
We also thank Manfred Schartl and Aki Shima for providing fish strains.
We are indebted to Peter Gruss for financial support (F.L.).This work was supported by fellowships of the Swiss National Science Foundation and the Ciba-Geigy-JubilaÈums-Stiftung
(F.L), and the Boehringer Ingelheim Foundation(R.W.K.) and a grant of the SFB 271 (J.W.).