Follow the mRNA: a new model for Bicoid gradient formation


Morphogens are molecules that specify cell fate in a concentration-dependent manner. A classic example is the Bicoid (BCD) protein, for which the prevailing model is that translation of bcd mRNA occurs from a point source at the anterior pole of the Drosophila melanogaster embryo followed by diffusion to produce a protein gradient. This model has been challenged by experiments showing that the diffusion rate of BCD is too slow to establish the protein gradient. The work described in a recent paper has solved this conundrum by demonstrating that a bcd mRNA gradient prefigures the BCD protein gradient.

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Figure 1: The diffusion-based model for formation of the Bicoid protein gradient.
Figure 2: Gradients of bicoid mRNA and Bicoid protein are nearly identical in early Drosophila melanogaster embryos.
Figure 3: The active mRNA transport and local translation model for formation of the Bicoid protein gradient.


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Sincere thanks to M. Noll and S. Baumgartner for providing the images used in figure 2. H.D.L.'s research on post-transcriptional regulation in D. melanogaster is supported by the Canadian Institutes for Health Research in the form of an operating grant (MOP-14409) and a team grant (CIHR Team in mRNP Systems Biology; CTP-79838).

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Lipshitz, H. Follow the mRNA: a new model for Bicoid gradient formation. Nat Rev Mol Cell Biol 10, 509–512 (2009).

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