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Divergent mechanisms regulate conserved cardiopharyngeal development and gene expression in distantly related ascidians.

Stolfi A, Lowe EK, Racioppi C, Ristoratore F, Brown CT, Swalla BJ, Christiaen L - Elife (2014)

Bottom Line: Ascidians present a striking dichotomy between conserved phenotypes and divergent genomes: embryonic cell lineages and gene expression patterns are conserved between distantly related species.Much research has focused on Ciona or Halocynthia spp. but development in other ascidians remains poorly characterized.In this study, we surveyed the multipotent myogenic B7.5 lineage in Molgula spp.

View Article: PubMed Central - PubMed

Affiliation: Center for Developmental Genetics, Department of Biology, New York University, New York, United States.

ABSTRACT
Ascidians present a striking dichotomy between conserved phenotypes and divergent genomes: embryonic cell lineages and gene expression patterns are conserved between distantly related species. Much research has focused on Ciona or Halocynthia spp. but development in other ascidians remains poorly characterized. In this study, we surveyed the multipotent myogenic B7.5 lineage in Molgula spp. Comparisons to the homologous lineage in Ciona revealed identical cell division and fate specification events that result in segregation of larval, cardiac, and pharyngeal muscle progenitors. Moreover, the expression patterns of key regulators are conserved, but cross-species transgenic assays uncovered incompatibility, or 'unintelligibility', of orthologous cis-regulatory sequences between Molgula and Ciona. These sequences drive identical expression patterns that are not recapitulated in cross-species assays. We show that this unintelligibility is likely due to changes in both cis- and trans-acting elements, hinting at widespread and frequent turnover of regulatory mechanisms underlying otherwise conserved aspects of ascidian embryogenesis.

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Moocci.Ets.b and Ciinte.Ets.b are functionally very similar.C. intestinalis embryos co-electroporated with Ciinte.Mesp>H2B::GFP (green), Ciinte.Foxf>mCherry (red), and various Ciinte.Mesp-driven perturbation constructs. Percentages represent the frequency of the phenotype seen in the representative image displayed for each condition. Overexpression of full-length Ets.b proteins from both C. intestinalis and M. occidentalis results ectopic Foxf+ TVCs at the expense of ATMs. The same conversion of ATMs to TVCs is seen for overexpression of Ets.b::VP16 fusions. Conversely, Ets.b::WRPW fusions repress TVC induction and Ciinte.Foxf reporter expression. As expected from the lack of sequence divergence predicted to affect DNA-binding specificities, Ets.b proteins from both species appear to be equally suited to trans-activating Ciinte.Foxf in C. intestinalis embryos. n = 100 for all conditions.DOI:http://dx.doi.org/10.7554/eLife.03728.027
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fig6s2: Moocci.Ets.b and Ciinte.Ets.b are functionally very similar.C. intestinalis embryos co-electroporated with Ciinte.Mesp>H2B::GFP (green), Ciinte.Foxf>mCherry (red), and various Ciinte.Mesp-driven perturbation constructs. Percentages represent the frequency of the phenotype seen in the representative image displayed for each condition. Overexpression of full-length Ets.b proteins from both C. intestinalis and M. occidentalis results ectopic Foxf+ TVCs at the expense of ATMs. The same conversion of ATMs to TVCs is seen for overexpression of Ets.b::VP16 fusions. Conversely, Ets.b::WRPW fusions repress TVC induction and Ciinte.Foxf reporter expression. As expected from the lack of sequence divergence predicted to affect DNA-binding specificities, Ets.b proteins from both species appear to be equally suited to trans-activating Ciinte.Foxf in C. intestinalis embryos. n = 100 for all conditions.DOI:http://dx.doi.org/10.7554/eLife.03728.027

Mentions: We asked whether the observed unintelligibility was indicative of changes in Ets.b protein properties between C. intestinalis and M. occidentalis embryo. At first glance, differences in DNA binding domain amino acid sequences between the Ets.b orthologs do not predict a change in binding site preference (Donaldson et al., 1996). Indeed, full-length Moocci.Ets.b and Moocci.Ets.b::VP16 were just as effective as their C. intestinalis counterparts to induce ectopic TVCs when expressed in the C. intestinalis B7.5 lineage (Figure 6—figure supplement 2). Moreover, C. intestinalis TVC induction was abolished by expression of the constitutive repressor form (Moocci.Ets.b::WRPW). However, neither full-length Moocci.Ets.b nor Moocci.Ets.b::VP16 was sufficient to induce activation of Moocci.Foxf reporter in C. intestinalis embryos (Figure 6—figure supplement 3). These surprising results suggest that, even though TVC induction and TVC-specific Foxf expression depends upon Ets.b-mediated MAPK activity in M. occidentalis embryos, there are profound species-specific differences in the regulatory mechanisms acting in parallel to MAPK/Ets.b upstream of Foxf, reflected in the mutual unintelligibility of the orthologous enhancers.


Divergent mechanisms regulate conserved cardiopharyngeal development and gene expression in distantly related ascidians.

Stolfi A, Lowe EK, Racioppi C, Ristoratore F, Brown CT, Swalla BJ, Christiaen L - Elife (2014)

Moocci.Ets.b and Ciinte.Ets.b are functionally very similar.C. intestinalis embryos co-electroporated with Ciinte.Mesp>H2B::GFP (green), Ciinte.Foxf>mCherry (red), and various Ciinte.Mesp-driven perturbation constructs. Percentages represent the frequency of the phenotype seen in the representative image displayed for each condition. Overexpression of full-length Ets.b proteins from both C. intestinalis and M. occidentalis results ectopic Foxf+ TVCs at the expense of ATMs. The same conversion of ATMs to TVCs is seen for overexpression of Ets.b::VP16 fusions. Conversely, Ets.b::WRPW fusions repress TVC induction and Ciinte.Foxf reporter expression. As expected from the lack of sequence divergence predicted to affect DNA-binding specificities, Ets.b proteins from both species appear to be equally suited to trans-activating Ciinte.Foxf in C. intestinalis embryos. n = 100 for all conditions.DOI:http://dx.doi.org/10.7554/eLife.03728.027
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4356046&req=5

fig6s2: Moocci.Ets.b and Ciinte.Ets.b are functionally very similar.C. intestinalis embryos co-electroporated with Ciinte.Mesp>H2B::GFP (green), Ciinte.Foxf>mCherry (red), and various Ciinte.Mesp-driven perturbation constructs. Percentages represent the frequency of the phenotype seen in the representative image displayed for each condition. Overexpression of full-length Ets.b proteins from both C. intestinalis and M. occidentalis results ectopic Foxf+ TVCs at the expense of ATMs. The same conversion of ATMs to TVCs is seen for overexpression of Ets.b::VP16 fusions. Conversely, Ets.b::WRPW fusions repress TVC induction and Ciinte.Foxf reporter expression. As expected from the lack of sequence divergence predicted to affect DNA-binding specificities, Ets.b proteins from both species appear to be equally suited to trans-activating Ciinte.Foxf in C. intestinalis embryos. n = 100 for all conditions.DOI:http://dx.doi.org/10.7554/eLife.03728.027
Mentions: We asked whether the observed unintelligibility was indicative of changes in Ets.b protein properties between C. intestinalis and M. occidentalis embryo. At first glance, differences in DNA binding domain amino acid sequences between the Ets.b orthologs do not predict a change in binding site preference (Donaldson et al., 1996). Indeed, full-length Moocci.Ets.b and Moocci.Ets.b::VP16 were just as effective as their C. intestinalis counterparts to induce ectopic TVCs when expressed in the C. intestinalis B7.5 lineage (Figure 6—figure supplement 2). Moreover, C. intestinalis TVC induction was abolished by expression of the constitutive repressor form (Moocci.Ets.b::WRPW). However, neither full-length Moocci.Ets.b nor Moocci.Ets.b::VP16 was sufficient to induce activation of Moocci.Foxf reporter in C. intestinalis embryos (Figure 6—figure supplement 3). These surprising results suggest that, even though TVC induction and TVC-specific Foxf expression depends upon Ets.b-mediated MAPK activity in M. occidentalis embryos, there are profound species-specific differences in the regulatory mechanisms acting in parallel to MAPK/Ets.b upstream of Foxf, reflected in the mutual unintelligibility of the orthologous enhancers.

Bottom Line: Ascidians present a striking dichotomy between conserved phenotypes and divergent genomes: embryonic cell lineages and gene expression patterns are conserved between distantly related species.Much research has focused on Ciona or Halocynthia spp. but development in other ascidians remains poorly characterized.In this study, we surveyed the multipotent myogenic B7.5 lineage in Molgula spp.

View Article: PubMed Central - PubMed

Affiliation: Center for Developmental Genetics, Department of Biology, New York University, New York, United States.

ABSTRACT
Ascidians present a striking dichotomy between conserved phenotypes and divergent genomes: embryonic cell lineages and gene expression patterns are conserved between distantly related species. Much research has focused on Ciona or Halocynthia spp. but development in other ascidians remains poorly characterized. In this study, we surveyed the multipotent myogenic B7.5 lineage in Molgula spp. Comparisons to the homologous lineage in Ciona revealed identical cell division and fate specification events that result in segregation of larval, cardiac, and pharyngeal muscle progenitors. Moreover, the expression patterns of key regulators are conserved, but cross-species transgenic assays uncovered incompatibility, or 'unintelligibility', of orthologous cis-regulatory sequences between Molgula and Ciona. These sequences drive identical expression patterns that are not recapitulated in cross-species assays. We show that this unintelligibility is likely due to changes in both cis- and trans-acting elements, hinting at widespread and frequent turnover of regulatory mechanisms underlying otherwise conserved aspects of ascidian embryogenesis.

Show MeSH
Related in: MedlinePlus