Evidence of a bicoid mRNA gradient refutes the SDD model which proposes that the Bicoid protein gradient arises through diffusion of the Bicoid protein. Read also our 2009 paper and our recent paper (2014) on how the bicoid mRNA is transported in the embryo to the posterior. Also read how, with the help of microtubules and the motor protein Ncd, the bicoid mRNA gradient is formed which is then the template for translation to form the protein gradient.
Read also a 2009 Nature Molecular Cell Biology review on the bicoid story, or a description of the whole story in a somewhat more gossip style in LabTimes here.
Watch 2 YouTube movies on bicoid mRNA gradient formation: