Homeotic protein bicoid

[4][5] Bicoid mRNA is actively localized to the anterior of the fruit fly egg during oogenesis[6] along microtubules[7] by the motor protein dynein,[8] and retained there through association with cortical actin.

[12][13][14] Bicoid protein represses the translation of caudal mRNA and enhances the transcription of anterior gap genes including hunchback, orthodenticle, and buttonhead.

[15] Bicoid contains an arginine-rich motif (part of the helix shown axially in this image) that is similar to the one found in the HIV protein REV and is essential for its nucleic acid binding.

The proper spatial expression of downstream genes relies on the robustness of this gradient to common variations between embryos, including in the number of maternally-deposited bicoid mRNAs and in egg size.

Comparative phylogenetic[17] and experimental evolution[18] studies suggest an inherent mechanism for robust generation of a scaled Bicoid protein gradient.

(Top) Nuclear Bicoid protein gradient in a fixed transgenic Drosophila embryo carrying a Bicoid–GFP fusion gene. Image courtesy of Julien O. Dubuis and Thomas Gregor. (Bottom) Bicoid–GFP protein (green) and FISH-labeled bicoid mRNA (red) in the anterior tip of a fixed transgenic Drosophila embryo. Both embryos are oriented with the anterior pole at left. Image courtesy of Shawn C. Little and Thomas Gregor (see Little et al. for methods [ 1 ] ).
PyMOL rendering of Bicoid homeodomain bound to its consensus site
Bicoid mutant
Bicoid mutant produces no head