Daniel St Johnston is a Wellcome Trust Principal Fellow in Cambridge. He has made major contributions to cell and developmental biology through his work on pattern formation in the Drosophila embryo. His career started with the cloning of the Drosophila decapentaplegic gene. This was the first example of an embryonic signalling molecule, and the dpp protein proved to be homologous to BMP4, a gene product that is involved in the development of all vertebrates and, in the adult animal, in bone repair. His subsequent work as a postdoctoral fellow was equally exciting, involving as it did the mechanisms of localisation of the Drosophila anterior determinant bicoid. On moving to the Cambridge, he maintained his interest in RNA localisation and succeeded in cloning and characterising the first example of an RNA-binding protein involved in mRNA localisation. He has been able to visualise microtubule-dependent RNA transport in vivo, and such work has recently been shown to apply to mammals. In addition to these studies, Daniel St Johnston has led the analysis of antero-posterior patterning in Drosophila through his observation that polarity originates from the positioning of the oocyte at the posterior end of the germ line cyst. The double signalling mechanism he has identified provided the first explanation for the establishment of orthogonal axes in any organism.He was awarded the EMBO Gold Medal in 2000.