Limits...
Hox genes control vertebrate body elongation by collinear Wnt repression.

Denans N, Iimura T, Pourquié O - Elife (2015)

Bottom Line: Our data indicate that a subset of progressively more posterior Hox genes, which are collinearly activated in vertebral precursors, repress Wnt activity with increasing strength.This leads to a graded repression of the Brachyury/T transcription factor, reducing mesoderm ingression and slowing down the elongation process.Due to the continuation of somite formation, this mechanism leads to the progressive reduction of PSM size.

View Article: PubMed Central - PubMed

Affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, University of Strasbourg, Illkirch, France.

ABSTRACT
In vertebrates, the total number of vertebrae is precisely defined. Vertebrae derive from embryonic somites that are continuously produced posteriorly from the presomitic mesoderm (PSM) during body formation. We show that in the chicken embryo, activation of posterior Hox genes (paralogs 9-13) in the tail-bud correlates with the slowing down of axis elongation. Our data indicate that a subset of progressively more posterior Hox genes, which are collinearly activated in vertebral precursors, repress Wnt activity with increasing strength. This leads to a graded repression of the Brachyury/T transcription factor, reducing mesoderm ingression and slowing down the elongation process. Due to the continuation of somite formation, this mechanism leads to the progressive reduction of PSM size. This ultimately brings the retinoic acid (RA)-producing segmented region in close vicinity to the tail bud, potentially accounting for the termination of segmentation and axis elongation.

Show MeSH

Related in: MedlinePlus

The posterior Hox genes regulate cell ingressionwith increasing strength.(A) Embryos consecutively electroporated withHoxd10-Cherry and Hoxc11-Venus(left) and with Hoxc11-Cherry andHoxa13-Venus (right). Arrowheads: anterior boundaryof Cherry (red) and Venus (green) domains. (B) Ratio ofVenus over Cherry domains corresponding to A. This showsthat Hoxa13 retains the cell longer in the epiblast thanHoxc11 which retains the cell longer thanHoxd10.DOI:http://dx.doi.org/10.7554/eLife.04379.009
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4384752&req=5

fig3s1: The posterior Hox genes regulate cell ingressionwith increasing strength.(A) Embryos consecutively electroporated withHoxd10-Cherry and Hoxc11-Venus(left) and with Hoxc11-Cherry andHoxa13-Venus (right). Arrowheads: anterior boundaryof Cherry (red) and Venus (green) domains. (B) Ratio ofVenus over Cherry domains corresponding to A. This showsthat Hoxa13 retains the cell longer in the epiblast thanHoxc11 which retains the cell longer thanHoxd10.DOI:http://dx.doi.org/10.7554/eLife.04379.009

Mentions: In order to test the role of posterior Hox genes on the control ofcell ingression and cell motility in the developing chicken embryo, we used an invivo electroporation technique, allowing to precisely target the paraxial mesodermprecursors in the epiblast of the anterior primitive streak (Bénazéraf et al., 2010) (Video 3). We developed a strategy allowing to overexpress twodifferent sets of constructs in largely different populations of paraxial mesodermcells by performing two consecutive electroporations of the paraxial mesoderm (PM)precursors of the epiblast of stage 4–5 HH embryos. Embryos are firstelectroporated on the left side of the primitive streak with a control Cherryconstruct, and then on the right side of the streak with a second vector expressingthe yellow fluorescent protein Venus and a Hox construct (Figure 3A). This strategy results in essentiallydifferent PM cells expressing the two sets of constructs with the Cherry expressingcells enriched on the left side whereas Hox expressing cells are mostly found on theright side. When no Hox construct is present in the Venus vector,the Cherry and Venus-expressing populations of cells were observed to extend from thetail-bud to the same antero-posterior level of the paraxial mesoderm indicating thatthey began ingressing at the same time (Figure3B, n = 8 embryos). In contrast, cells expressing Cherry were alwaysextending more anteriorly than cells expressing Venus and one of the followingposterior Hox gene: Hoxa9, Hoxc9, Hoxd10, Hoxd11, Hoxc11,Hoxa13, Hoxb13, or Hoxc13, indicating that theseHox genes can delay cell ingression of the PSM progenitors (Figure 3B–C n > 6 for eachcondition and not shown). This simply reflects the fact that cells ingressing laterbecome located more posteriorly. Strikingly, the effect on ingression wasprogressively stronger when overexpressing more 5′ genes suggesting acollinear trend (Figure 3C). Inverting theorder in which the constructs are electroporated did not affect the final phenotype.The distance between the anterior boundaries of the two domains was found toprogressively increase with more posterior Hox genes as shown bymeasuring the ratio between Venus and Cherry posterior domains (Figure 3A–C). Over-expression of Hoxa10, Hoxc10,Hoxa11, Hoxc12, Hoxd12 and Hoxd13 showed no difference with the controlCherry vector (Figure 3A–C, n >6 for each condition and data not shown). Using consecutive electroporation ofHoxd10 and Hoxc11 constructs labeled with Cherryand Venus, respectively, we observed that Hoxc11 has a strongereffect on ingression than Hoxd10 (Figure 3—figure supplement 1, n = 12 embryos). A similarresult was observed when Hoxa13 was compared toHoxc11 in the same assay (Figure 3—figure supplement 1, n = 6 embryos). Thus, a subsetof posterior Hox genes is able to delay PSM cell ingression in acollinear manner.Video 3.Time-lapse video showing the precise targeting of PSM progenitors andthe ingression of the epiblast cells to form the PSM.


Hox genes control vertebrate body elongation by collinear Wnt repression.

Denans N, Iimura T, Pourquié O - Elife (2015)

The posterior Hox genes regulate cell ingressionwith increasing strength.(A) Embryos consecutively electroporated withHoxd10-Cherry and Hoxc11-Venus(left) and with Hoxc11-Cherry andHoxa13-Venus (right). Arrowheads: anterior boundaryof Cherry (red) and Venus (green) domains. (B) Ratio ofVenus over Cherry domains corresponding to A. This showsthat Hoxa13 retains the cell longer in the epiblast thanHoxc11 which retains the cell longer thanHoxd10.DOI:http://dx.doi.org/10.7554/eLife.04379.009
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384752&req=5

fig3s1: The posterior Hox genes regulate cell ingressionwith increasing strength.(A) Embryos consecutively electroporated withHoxd10-Cherry and Hoxc11-Venus(left) and with Hoxc11-Cherry andHoxa13-Venus (right). Arrowheads: anterior boundaryof Cherry (red) and Venus (green) domains. (B) Ratio ofVenus over Cherry domains corresponding to A. This showsthat Hoxa13 retains the cell longer in the epiblast thanHoxc11 which retains the cell longer thanHoxd10.DOI:http://dx.doi.org/10.7554/eLife.04379.009
Mentions: In order to test the role of posterior Hox genes on the control ofcell ingression and cell motility in the developing chicken embryo, we used an invivo electroporation technique, allowing to precisely target the paraxial mesodermprecursors in the epiblast of the anterior primitive streak (Bénazéraf et al., 2010) (Video 3). We developed a strategy allowing to overexpress twodifferent sets of constructs in largely different populations of paraxial mesodermcells by performing two consecutive electroporations of the paraxial mesoderm (PM)precursors of the epiblast of stage 4–5 HH embryos. Embryos are firstelectroporated on the left side of the primitive streak with a control Cherryconstruct, and then on the right side of the streak with a second vector expressingthe yellow fluorescent protein Venus and a Hox construct (Figure 3A). This strategy results in essentiallydifferent PM cells expressing the two sets of constructs with the Cherry expressingcells enriched on the left side whereas Hox expressing cells are mostly found on theright side. When no Hox construct is present in the Venus vector,the Cherry and Venus-expressing populations of cells were observed to extend from thetail-bud to the same antero-posterior level of the paraxial mesoderm indicating thatthey began ingressing at the same time (Figure3B, n = 8 embryos). In contrast, cells expressing Cherry were alwaysextending more anteriorly than cells expressing Venus and one of the followingposterior Hox gene: Hoxa9, Hoxc9, Hoxd10, Hoxd11, Hoxc11,Hoxa13, Hoxb13, or Hoxc13, indicating that theseHox genes can delay cell ingression of the PSM progenitors (Figure 3B–C n > 6 for eachcondition and not shown). This simply reflects the fact that cells ingressing laterbecome located more posteriorly. Strikingly, the effect on ingression wasprogressively stronger when overexpressing more 5′ genes suggesting acollinear trend (Figure 3C). Inverting theorder in which the constructs are electroporated did not affect the final phenotype.The distance between the anterior boundaries of the two domains was found toprogressively increase with more posterior Hox genes as shown bymeasuring the ratio between Venus and Cherry posterior domains (Figure 3A–C). Over-expression of Hoxa10, Hoxc10,Hoxa11, Hoxc12, Hoxd12 and Hoxd13 showed no difference with the controlCherry vector (Figure 3A–C, n >6 for each condition and data not shown). Using consecutive electroporation ofHoxd10 and Hoxc11 constructs labeled with Cherryand Venus, respectively, we observed that Hoxc11 has a strongereffect on ingression than Hoxd10 (Figure 3—figure supplement 1, n = 12 embryos). A similarresult was observed when Hoxa13 was compared toHoxc11 in the same assay (Figure 3—figure supplement 1, n = 6 embryos). Thus, a subsetof posterior Hox genes is able to delay PSM cell ingression in acollinear manner.Video 3.Time-lapse video showing the precise targeting of PSM progenitors andthe ingression of the epiblast cells to form the PSM.

Bottom Line: Our data indicate that a subset of progressively more posterior Hox genes, which are collinearly activated in vertebral precursors, repress Wnt activity with increasing strength.This leads to a graded repression of the Brachyury/T transcription factor, reducing mesoderm ingression and slowing down the elongation process.Due to the continuation of somite formation, this mechanism leads to the progressive reduction of PSM size.

View Article: PubMed Central - PubMed

Affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, University of Strasbourg, Illkirch, France.

ABSTRACT
In vertebrates, the total number of vertebrae is precisely defined. Vertebrae derive from embryonic somites that are continuously produced posteriorly from the presomitic mesoderm (PSM) during body formation. We show that in the chicken embryo, activation of posterior Hox genes (paralogs 9-13) in the tail-bud correlates with the slowing down of axis elongation. Our data indicate that a subset of progressively more posterior Hox genes, which are collinearly activated in vertebral precursors, repress Wnt activity with increasing strength. This leads to a graded repression of the Brachyury/T transcription factor, reducing mesoderm ingression and slowing down the elongation process. Due to the continuation of somite formation, this mechanism leads to the progressive reduction of PSM size. This ultimately brings the retinoic acid (RA)-producing segmented region in close vicinity to the tail bud, potentially accounting for the termination of segmentation and axis elongation.

Show MeSH
Related in: MedlinePlus