Homeotic protein bicoid explained

Uniprot:P09081
Organism:Drosophila melanogaster
Homeotic protein bicoid
Symbol:bcd

Homeotic protein bicoid is encoded by the bcd maternal effect gene in Drosophilia. Homeotic protein bicoid concentration gradient patterns the anterior-posterior (A-P) axis during Drosophila embryogenesis. Bicoid was the first protein demonstrated to act as a morphogen.[1] Although bicoid is important for the development of Drosophila and other higher dipterans,[2] it is absent from most other insects, where its role is accomplished by other genes.[3] [4]

Role in axial patterning

Bicoid mRNA is actively localized to the anterior of the fruit fly egg during oogenesis[5] along microtubules[6] by the motor protein dynein,[7] and retained there through association with cortical actin.[8] Translation of bicoid is regulated by its 3′ UTR and begins after egg deposition. Diffusion and convection within the syncytium produce an exponential gradient of Bicoid protein[9] within roughly one hour, after which Bicoid nuclear concentrations remain approximately constant through cellularization.[10] An alternative model proposes the formation of a bicoid mRNA gradient in the embryo along cortical microtubules which then serves as template for translation of the Bicoid protein to form the Bicoid protein gradient.[11] [12] [13] Bicoid protein represses the translation of caudal mRNA and enhances the transcription of anterior gap genes including hunchback, orthodenticle, and buttonhead.

Structure and function

Bicoid is one of the few proteins which uses its homeodomain to bind both DNA and RNA targets to regulate their transcription and translation, respectively. The nucleic acid-binding homeodomain of Bicoid has been solved by NMR.[14] 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.[15] Bicoid protein gradient formation is one of the earliest steps in fruit fly embryo A-P patterning. 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[16] and experimental evolution[17] studies suggest an inherent mechanism for robust generation of a scaled Bicoid protein gradient. Mechanisms that have been proposed to effect this scaling include non-linear degradation of Bicoid,[18] nuclear retention as a size-dependent regulator of Bicoid protein's effective diffusion coefficient,[19] and scaling of cytoplasmic streaming.

See also

Notes and References

  1. Driever W, Nüsslein-Volhard C . The bicoid protein determines position in the Drosophila embryo in a concentration-dependent manner . Cell . 54 . 1 . 95–104 . July 1988 . 3383245 . 10.1016/0092-8674(88)90183-3 . 18830552 .
  2. Gregor T, McGregor AP, Wieschaus EF . Shape and function of the Bicoid morphogen gradient in dipteran species with different sized embryos . Developmental Biology . 316 . 2 . 350–358 . April 2008 . 18328473 . 2441567 . 10.1016/j.ydbio.2008.01.039 .
  3. Chouard T . Darwin 200: Beneath the surface . Nature . 456 . 7220 . 300–303 . November 2008 . 19020592 . 10.1038/456300a . free .
  4. Schröder R . The genes orthodenticle and hunchback substitute for bicoid in the beetle Tribolium . En . Nature . 422 . 6932 . 621–625 . April 2003 . 12687002 . 10.1038/nature01536 . 2003Natur.422..621S . 4406927 .
  5. St Johnston D, Driever W, Berleth T, Richstein S, Nusslein-Volhard C . 1989 . Multiple steps in the localization of bicoid RNA to the anterior pole of the Drosophila oocyte . Development . 107 . 2483989 . 13–19 . 10.1242/dev.107.Supplement.13 .
  6. Pokrywka NJ, Stephenson EC . Microtubules mediate the localization of bicoid RNA during Drosophila oogenesis . Development . 113 . 1 . 55–66 . September 1991 . 10.1242/dev.113.1.55 . 1684934 . free .
  7. Weil TT, Forrest KM, Gavis ER . Localization of bicoid mRNA in late oocytes is maintained by continual active transport . Developmental Cell . 11 . 2 . 251–262 . August 2006 . 16890164 . 10.1016/j.devcel.2006.06.006 . free .
  8. Weil TT, Parton R, Davis I, Gavis ER . Changes in bicoid mRNA anchoring highlight conserved mechanisms during the oocyte-to-embryo transition . Current Biology . 18 . 14 . 1055–1061 . July 2008 . 18639459 . 2581475 . 10.1016/j.cub.2008.06.046 . 2008CBio...18.1055W .
  9. Hecht I, Rappel WJ, Levine H . Determining the scale of the Bicoid morphogen gradient . Proceedings of the National Academy of Sciences of the United States of America . 106 . 6 . 1710–1715 . February 2009 . 19190186 . 2644102 . 10.1073/pnas.0807655106 . 2009PNAS..106.1710H . free .
  10. Gregor T, Wieschaus EF, McGregor AP, Bialek W, Tank DW . Stability and nuclear dynamics of the bicoid morphogen gradient . Cell . 130 . 1 . 141–152 . July 2007 . 17632061 . 2253672 . 10.1016/j.cell.2007.05.026 .
  11. Frigerio G, Burri M, Bopp D, Baumgartner S, Noll M . Structure of the segmentation gene paired and the Drosophila PRD gene set as part of a gene network . Cell . 47 . 5 . 735–746 . December 1986 . 2877746 . 10.1016/0092-8674(86)90516-7 . 9658875 .
  12. Spirov A, Fahmy K, Schneider M, Frei E, Noll M, Baumgartner S . Formation of the bicoid morphogen gradient: an mRNA gradient dictates the protein gradient . Development . 136 . 4 . 605–614 . February 2009 . 19168676 . 2685955 . 10.1242/dev.031195 .
  13. Fahmy K, Akber M, Cai X, Koul A, Hayder A, Baumgartner S . αTubulin 67C and Ncd are essential for establishing a cortical microtubular network and formation of the Bicoid mRNA gradient in Drosophila . PLOS ONE . 9 . 11 . e112053 . 2014 . 25390693 . 4229129 . 10.1371/journal.pone.0112053 . 2014PLoSO...9k2053F . free .
  14. Baird-Titus JM, Clark-Baldwin K, Dave V, Caperelli CA, Ma J, Rance M . The solution structure of the native K50 Bicoid homeodomain bound to the consensus TAATCC DNA-binding site . Journal of Molecular Biology . 356 . 5 . 1137–1151 . March 2006 . 16406070 . 10.1016/j.jmb.2005.12.007 .
  15. Niessing D, Driever W, Sprenger F, Taubert H, Jäckle H, Rivera-Pomar R . Homeodomain position 54 specifies transcriptional versus translational control by Bicoid . Molecular Cell . 5 . 2 . 395–401 . February 2000 . 10882080 . 10.1016/S1097-2765(00)80434-7 . 11858/00-001M-0000-0028-A069-9 . free .
  16. Gregor T, McGregor AP, Wieschaus EF . Shape and function of the Bicoid morphogen gradient in dipteran species with different sized embryos . Developmental Biology . 316 . 2 . 350–358 . April 2008 . 18328473 . 2441567 . 10.1016/j.ydbio.2008.01.039 .
  17. Cheung D, Miles C, Kreitman M, Ma J . Adaptation of the length scale and amplitude of the Bicoid gradient profile to achieve robust patterning in abnormally large Drosophila melanogaster embryos . Development . 141 . 1 . 124–135 . January 2014 . 24284208 . 3865754 . 10.1242/dev.098640 .
  18. Eldar A, Rosin D, Shilo BZ, Barkai N . Self-enhanced ligand degradation underlies robustness of morphogen gradients . Developmental Cell . 5 . 4 . 635–646 . October 2003 . 14536064 . 10.1016/S1534-5807(03)00292-2 . free .
  19. Grimm O, Wieschaus E . The Bicoid gradient is shaped independently of nuclei . Development . 137 . 17 . 2857–2862 . September 2010 . 20699297 . 2938918 . 10.1242/dev.052589 .

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