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

Posterior prevalence of posterior Hox genes.(A) Embryos consecutively electroporated first withHoxc11-Cherry +Hoxc11mutH-Cherry and with Hoxd10-Venus+ Hoxc11-Venus shown 24 hr after reincubation.(B) Embryos consecutively electroporated first withHoxa13-Cherry +Hoxa13mutH-Cherry and then withHoxa13-Venus + Hoxc11-Venusshown 24 hr after reincubation. Red arrowheads: anterior boundary ofCherry-expressing cells. Green arrowheads: anterior boundary ofVenus-expressing cells. (C) Quantification of the ratio ofVenus over Cherry expressing domains for the experiments shown inA and B. Each dot corresponds to oneelectroporated embryo and bar indicates the mean.(D–E) Luciferase assay measuringWnt/βcatenin pathway activity after over-expression of the BATLucconstruct together with a Renilla-expressing vector and either(D) control, Hoxa9, Hoxa13or the combination of Hoxa9 and Hoxa13expressing vectors. (E) Blow-up of the samples shown in(D). (F) BATLuc assay with serial dilutions ofthe Hoxa13 plasmid (in μg/μl on the x axis).(G) Western blot labeled with an anti-HA antibody showingembryos electroporated with Hoxa13 under the control of adoxycycline-responsive promoter activated with different doses ofdoxycycline (in μg/ml). (H) BATLuc assay afterHoxa13 over-expression under the control of adoxycycline-responsive promoter activated with different doses ofdoxycycline (in μg/ml on the x axis). Stars represent the p value ofthe two-tailed Student's t-test applied between thedifferent conditions. **p < 0.01;***p < 0.005. Error bars represent the standarderror to the mean (SEM).DOI:http://dx.doi.org/10.7554/eLife.04379.011
© Copyright Policy
Related In: Results  -  Collection

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

fig6: Posterior prevalence of posterior Hox genes.(A) Embryos consecutively electroporated first withHoxc11-Cherry +Hoxc11mutH-Cherry and with Hoxd10-Venus+ Hoxc11-Venus shown 24 hr after reincubation.(B) Embryos consecutively electroporated first withHoxa13-Cherry +Hoxa13mutH-Cherry and then withHoxa13-Venus + Hoxc11-Venusshown 24 hr after reincubation. Red arrowheads: anterior boundary ofCherry-expressing cells. Green arrowheads: anterior boundary ofVenus-expressing cells. (C) Quantification of the ratio ofVenus over Cherry expressing domains for the experiments shown inA and B. Each dot corresponds to oneelectroporated embryo and bar indicates the mean.(D–E) Luciferase assay measuringWnt/βcatenin pathway activity after over-expression of the BATLucconstruct together with a Renilla-expressing vector and either(D) control, Hoxa9, Hoxa13or the combination of Hoxa9 and Hoxa13expressing vectors. (E) Blow-up of the samples shown in(D). (F) BATLuc assay with serial dilutions ofthe Hoxa13 plasmid (in μg/μl on the x axis).(G) Western blot labeled with an anti-HA antibody showingembryos electroporated with Hoxa13 under the control of adoxycycline-responsive promoter activated with different doses ofdoxycycline (in μg/ml). (H) BATLuc assay afterHoxa13 over-expression under the control of adoxycycline-responsive promoter activated with different doses ofdoxycycline (in μg/ml on the x axis). Stars represent the p value ofthe two-tailed Student's t-test applied between thedifferent conditions. **p < 0.01;***p < 0.005. Error bars represent the standarderror to the mean (SEM).DOI:http://dx.doi.org/10.7554/eLife.04379.011

Mentions: In Drosophila and vertebrates, Hox genes expressedposteriorly can suppress the function of more anterior ones, a property termedphenotypic suppression or posterior prevalence (Duboule and Morata, 1994). We previously showed that posterior prevalenceapplies for the control of cell ingression by Hoxb1-9 genes (Iimura and Pourquié, 2006). To testwhether this property also applies to the posterior Hox genes withan effect on axis elongation, we performed consecutive electroporations first with amix of Hoxd10 and Hoxc11 constructs (leading toexpression in the same cells, in green Figure6A) and then with a mix of Hoxc11 and a control construct(a mutated Hoxc11 unable to bind DNA (Hoxc11mutH),in red Figure 6A). We observed that cellsover-expressing the two functional Hox genes reach the same anteriorposition as cells over-expressing Hoxc11 and control (Figure 6A,C, n = 10 embryos). ThusHoxc11 function is dominant over Hoxd10.Similarly, we observed dominance of Hoxa13 overHoxc11 in the same assay (Figure6B,C, n = 8 embryos). Therefore, posterior prevalence appears togenerally apply for Hox control of cell ingression in the mesoderm(Iimura and Pourquié, 2006). As aresult, the effect of Hox genes on cell retention in the epiblastshould become progressively stronger as more posterior genes become activated.10.7554/eLife.04379.011Figure 6.Posterior prevalence of posterior Hox genes.


Hox genes control vertebrate body elongation by collinear Wnt repression.

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

Posterior prevalence of posterior Hox genes.(A) Embryos consecutively electroporated first withHoxc11-Cherry +Hoxc11mutH-Cherry and with Hoxd10-Venus+ Hoxc11-Venus shown 24 hr after reincubation.(B) Embryos consecutively electroporated first withHoxa13-Cherry +Hoxa13mutH-Cherry and then withHoxa13-Venus + Hoxc11-Venusshown 24 hr after reincubation. Red arrowheads: anterior boundary ofCherry-expressing cells. Green arrowheads: anterior boundary ofVenus-expressing cells. (C) Quantification of the ratio ofVenus over Cherry expressing domains for the experiments shown inA and B. Each dot corresponds to oneelectroporated embryo and bar indicates the mean.(D–E) Luciferase assay measuringWnt/βcatenin pathway activity after over-expression of the BATLucconstruct together with a Renilla-expressing vector and either(D) control, Hoxa9, Hoxa13or the combination of Hoxa9 and Hoxa13expressing vectors. (E) Blow-up of the samples shown in(D). (F) BATLuc assay with serial dilutions ofthe Hoxa13 plasmid (in μg/μl on the x axis).(G) Western blot labeled with an anti-HA antibody showingembryos electroporated with Hoxa13 under the control of adoxycycline-responsive promoter activated with different doses ofdoxycycline (in μg/ml). (H) BATLuc assay afterHoxa13 over-expression under the control of adoxycycline-responsive promoter activated with different doses ofdoxycycline (in μg/ml on the x axis). Stars represent the p value ofthe two-tailed Student's t-test applied between thedifferent conditions. **p < 0.01;***p < 0.005. Error bars represent the standarderror to the mean (SEM).DOI:http://dx.doi.org/10.7554/eLife.04379.011
© Copyright Policy
Related In: Results  -  Collection

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

fig6: Posterior prevalence of posterior Hox genes.(A) Embryos consecutively electroporated first withHoxc11-Cherry +Hoxc11mutH-Cherry and with Hoxd10-Venus+ Hoxc11-Venus shown 24 hr after reincubation.(B) Embryos consecutively electroporated first withHoxa13-Cherry +Hoxa13mutH-Cherry and then withHoxa13-Venus + Hoxc11-Venusshown 24 hr after reincubation. Red arrowheads: anterior boundary ofCherry-expressing cells. Green arrowheads: anterior boundary ofVenus-expressing cells. (C) Quantification of the ratio ofVenus over Cherry expressing domains for the experiments shown inA and B. Each dot corresponds to oneelectroporated embryo and bar indicates the mean.(D–E) Luciferase assay measuringWnt/βcatenin pathway activity after over-expression of the BATLucconstruct together with a Renilla-expressing vector and either(D) control, Hoxa9, Hoxa13or the combination of Hoxa9 and Hoxa13expressing vectors. (E) Blow-up of the samples shown in(D). (F) BATLuc assay with serial dilutions ofthe Hoxa13 plasmid (in μg/μl on the x axis).(G) Western blot labeled with an anti-HA antibody showingembryos electroporated with Hoxa13 under the control of adoxycycline-responsive promoter activated with different doses ofdoxycycline (in μg/ml). (H) BATLuc assay afterHoxa13 over-expression under the control of adoxycycline-responsive promoter activated with different doses ofdoxycycline (in μg/ml on the x axis). Stars represent the p value ofthe two-tailed Student's t-test applied between thedifferent conditions. **p < 0.01;***p < 0.005. Error bars represent the standarderror to the mean (SEM).DOI:http://dx.doi.org/10.7554/eLife.04379.011
Mentions: In Drosophila and vertebrates, Hox genes expressedposteriorly can suppress the function of more anterior ones, a property termedphenotypic suppression or posterior prevalence (Duboule and Morata, 1994). We previously showed that posterior prevalenceapplies for the control of cell ingression by Hoxb1-9 genes (Iimura and Pourquié, 2006). To testwhether this property also applies to the posterior Hox genes withan effect on axis elongation, we performed consecutive electroporations first with amix of Hoxd10 and Hoxc11 constructs (leading toexpression in the same cells, in green Figure6A) and then with a mix of Hoxc11 and a control construct(a mutated Hoxc11 unable to bind DNA (Hoxc11mutH),in red Figure 6A). We observed that cellsover-expressing the two functional Hox genes reach the same anteriorposition as cells over-expressing Hoxc11 and control (Figure 6A,C, n = 10 embryos). ThusHoxc11 function is dominant over Hoxd10.Similarly, we observed dominance of Hoxa13 overHoxc11 in the same assay (Figure6B,C, n = 8 embryos). Therefore, posterior prevalence appears togenerally apply for Hox control of cell ingression in the mesoderm(Iimura and Pourquié, 2006). As aresult, the effect of Hox genes on cell retention in the epiblastshould become progressively stronger as more posterior genes become activated.10.7554/eLife.04379.011Figure 6.Posterior prevalence of posterior Hox genes.

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