Pre‐steady and stable morphogen gradients: can they coexist?

Mol Syst Biol. 6: 428In our recent paper (de Lachapelle and Bergmann, 2010), we studied two systems properties of early Drosophila embryo development: using staining images for three gap genes and the pair‐rule gene Eve that were produced in an earlier study (Bergmann et al , 2007), we investigated precision and scaling of their expression domains. These images were taken not only for wild‐type embryos, but also for embryos with single and quadruple dosage of maternal bicoid mRNA, inducing shifted expression domains. Interestingly, our careful quantification of precision and scaling indicates that these features are position‐dependent more than gene‐dependent. Indeed, when expression domains are shifted due to altered bicoid dosage, their precision and scaling properties seem to change according to their new position. In our view, this suggests that precision and scaling are, at least in part, already achieved at the level of the Bicoid gradient itself and then passed on to its target genes. Investigating models that can reproduce the position‐dependent signatures of precision and scaling at the gradient level, we identify two necessary ingredients: it is essential to include nuclear trapping and an external pre‐steady‐state morpohogen gradient to achieve both maximal precision at mid‐embryo and almost perfect …