View source for File:Hox 3 phase model.jpg

==Model representing the 3 phases (I, II, and III) of Hox action in Paraxial Mesoderm precursors in the Epiblast/tail-bud during Axis Elongation==

Model representing the 3 phases (I, II, and III) of Hox action in presomitic mesoderm (PSM) precursors in the epiblast/tail-bud during body axis elongation. 
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* '''Phase I''' - Anterior Hox genes (paralogs 1–9) are expressed. They control cell ingression in a Pbx1-dependent manner leading to the collinear positioning of Hox genes expression domains in the anterior region of the embryo. 
* '''Phase II''' - No Hox genes are activated during phase II, allowing fast elongation of the embryonic axis. 
* '''Phase III''' - posterior Hox genes (paralogs 9–13) are collinearly activated in PSM precursors. Our data suggest that collinear activation of posterior Hox genes leads to repression of Wnt signaling and its target T/Brachyury, which progressively increases in strength. This results in a progressive arrest of cell ingression in the PSM, leading to a decrease in axis elongation rate. Since the velocity of somite formation is roughly constant, PSM size starts to decrease when elongation velocity becomes slower than that of somite formation. During this latter phase the control of cell ingression by posterior Hox genes appears to be independent of Pbx1.
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* '''Pbx1''' - Pre-B-Cell Leukemia Transcription Factor 1 [http://www.omim.org/entry/176310 OMIM 176310]
* '''ss''' - somite stage
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:Links: [[Developmental_Signals_-_Homeobox|Hox]] | [[Chicken Development]] | [[Presomitic Mesoderm Migration|Presomitic Mesoderm Migration Movie]]


===Reference===
<pubmed>25719209</pubmed>| [http://elifesciences.org/content/4/e04379 Elife.]


====Copyright====
http://creativecommons.org/licenses/by/4.0/


Figure 11.  DOI: http://dx.doi.org/10.7554/eLife.04379.027

See more at: http://elifesciences.org/content/4/e04379#sthash.GdHelCTO.dpuf


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[[Category:Chicken]][[Category:Hox]][[Category:Wnt]]