The bicoid morphogen system.

Several fundamental concepts of developmental biology have emerged from studies on the early development of the Drosophila melanogaster embryo. In the late 1980s, studies on Bicoid provided the first solid experimental evidence for the existence of morphogenetic gradients and their implication in axial patterning. Bicoid has since stimulated further research, bringing together developmental and cell biologists, physicists and theoreticians to address fundamental biological questions. These include mechanistic aspects of transcriptional and translational control, molecular and functional aspects of evolution and, more recently with the development of quantitative approaches, the robustness of axial patterning in a systems biology view. However, recent studies provide data which lead to contradictory interpretations. Here, we discuss these recent observations, highlighting the data helping to understand how anterior patterning is achieved under the control of Bicoid and point to novel challenges for future studies.