Morphogen gradients provide key positional information during embryogenesis but how they are established is not well understood. A gradient of the transcription factor Bicoid is known to provide Drosophila embryos with positional information along their anterior-posterior axes. Since Bicoid is enriched in nuclei, nuclei have recently been proposed to act as potential traps or sites of degradation that could slow down Bicoid diffusion from the anterior pole and hence contribute to the observed Bicoid gradient. On , Oliver Grimm and Eric Wieschaus address this issue experimentally and find that the Bicoid gradient is shaped independently of nuclei. Using mutated Bicoid with impaired nuclear localisation, they show that the resulting gradient of this protein is indistinguishable from that formed by normal Bicoid protein. They also show that the initial centre-to-surface redistribution of Bicoid and the scaling of the gradient are not influenced by Bicoid nuclear accumulation. Based on these findings, the authors propose that nuclei do not play a role in shaping the Bicoid gradient.
