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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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Lhx3/4 proteins from M. occidentalis are sufficient to activate ectopic expression of endogenous Mesp in C. intestinalis.In situ hybridization for Ciinte.Mesp in 110-cell stage C. intestinalis embryos. (A) Expression of Ciinte.Mesp is restricted to the B7.5 blastomeres (solid arrowheads) in control embryos. (B) Ectopic Ciinte.Mesp expression is seen in a few cells (hollow arrowheads) in 39% (n = 100) of embryos electroporated with Ciinte.Tbx6-r.b>Moocci.Lhx3/4.b. (C) Ectopic Ciinte.Mesp expression is seen in a few cells (hollow arrowheads) in 74% (n = 100) of embryos electroporated with Ciinte.Tbx6-r.b>Moocci.Lhx3/4.a. (D) Ectopic Ciinte.Mesp expression is seen in a broad posterior swath of cells in 86% (n = 50) of embryos electroporated with Ciinte.Tbx6-r.b>Ciinte.Lhx3/4. All embryos viewed vegetally with the anterior to the top.DOI:http://dx.doi.org/10.7554/eLife.03728.022
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fig5s1: Lhx3/4 proteins from M. occidentalis are sufficient to activate ectopic expression of endogenous Mesp in C. intestinalis.In situ hybridization for Ciinte.Mesp in 110-cell stage C. intestinalis embryos. (A) Expression of Ciinte.Mesp is restricted to the B7.5 blastomeres (solid arrowheads) in control embryos. (B) Ectopic Ciinte.Mesp expression is seen in a few cells (hollow arrowheads) in 39% (n = 100) of embryos electroporated with Ciinte.Tbx6-r.b>Moocci.Lhx3/4.b. (C) Ectopic Ciinte.Mesp expression is seen in a few cells (hollow arrowheads) in 74% (n = 100) of embryos electroporated with Ciinte.Tbx6-r.b>Moocci.Lhx3/4.a. (D) Ectopic Ciinte.Mesp expression is seen in a broad posterior swath of cells in 86% (n = 50) of embryos electroporated with Ciinte.Tbx6-r.b>Ciinte.Lhx3/4. All embryos viewed vegetally with the anterior to the top.DOI:http://dx.doi.org/10.7554/eLife.03728.022

Mentions: Overexpression of Moocci.Tbx6-r.b but not Moocci.Tbx6-r.a was sufficient to activate ectopic Ciinte.Mesp reporter construct expression in vegetal pole cells (Figure 5A–C). In this regard, Moocci.Tbx6-r.b function seemed comparable to that of Ciinte.Tbx6-r.b (Figure 5D). Conversely, overexpression of either Lhx3/4.b or Lhx3/4.a from M. occidentalis in the posterior C. intestinalis embryo using the Ciinte.Tbx6-r.b promoter caused ectopic expression of both endogenous Ciinte.Mesp (Figure 5—figure supplement 1) and Ciinte.Mesp reporter construct (Figure 5E–G). These experiments revealed that both M. occidentalis Lhx3/4 proteins are conserved enough to activate low levels of Ciinte.Mesp expression (presumably by synergizing with endogenous Ciinte.Tbx6-r.b). However, neither was as effective as Ciinte.Lhx3/4 in activating Ciinte.Mesp (Figure 5H). These data suggested that cis/trans or trans/trans co-evolution involving the highly divergent Moocci.Lhx3/4.b paralog may only partially account for the incompatibility of Mesp cis-regulatory logic between the two species.10.7554/eLife.03728.021Figure 5.Divergence of Mesp regulation due to changes in cis and trans.


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)

Lhx3/4 proteins from M. occidentalis are sufficient to activate ectopic expression of endogenous Mesp in C. intestinalis.In situ hybridization for Ciinte.Mesp in 110-cell stage C. intestinalis embryos. (A) Expression of Ciinte.Mesp is restricted to the B7.5 blastomeres (solid arrowheads) in control embryos. (B) Ectopic Ciinte.Mesp expression is seen in a few cells (hollow arrowheads) in 39% (n = 100) of embryos electroporated with Ciinte.Tbx6-r.b>Moocci.Lhx3/4.b. (C) Ectopic Ciinte.Mesp expression is seen in a few cells (hollow arrowheads) in 74% (n = 100) of embryos electroporated with Ciinte.Tbx6-r.b>Moocci.Lhx3/4.a. (D) Ectopic Ciinte.Mesp expression is seen in a broad posterior swath of cells in 86% (n = 50) of embryos electroporated with Ciinte.Tbx6-r.b>Ciinte.Lhx3/4. All embryos viewed vegetally with the anterior to the top.DOI:http://dx.doi.org/10.7554/eLife.03728.022
© Copyright Policy
Related In: Results  -  Collection

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

fig5s1: Lhx3/4 proteins from M. occidentalis are sufficient to activate ectopic expression of endogenous Mesp in C. intestinalis.In situ hybridization for Ciinte.Mesp in 110-cell stage C. intestinalis embryos. (A) Expression of Ciinte.Mesp is restricted to the B7.5 blastomeres (solid arrowheads) in control embryos. (B) Ectopic Ciinte.Mesp expression is seen in a few cells (hollow arrowheads) in 39% (n = 100) of embryos electroporated with Ciinte.Tbx6-r.b>Moocci.Lhx3/4.b. (C) Ectopic Ciinte.Mesp expression is seen in a few cells (hollow arrowheads) in 74% (n = 100) of embryos electroporated with Ciinte.Tbx6-r.b>Moocci.Lhx3/4.a. (D) Ectopic Ciinte.Mesp expression is seen in a broad posterior swath of cells in 86% (n = 50) of embryos electroporated with Ciinte.Tbx6-r.b>Ciinte.Lhx3/4. All embryos viewed vegetally with the anterior to the top.DOI:http://dx.doi.org/10.7554/eLife.03728.022
Mentions: Overexpression of Moocci.Tbx6-r.b but not Moocci.Tbx6-r.a was sufficient to activate ectopic Ciinte.Mesp reporter construct expression in vegetal pole cells (Figure 5A–C). In this regard, Moocci.Tbx6-r.b function seemed comparable to that of Ciinte.Tbx6-r.b (Figure 5D). Conversely, overexpression of either Lhx3/4.b or Lhx3/4.a from M. occidentalis in the posterior C. intestinalis embryo using the Ciinte.Tbx6-r.b promoter caused ectopic expression of both endogenous Ciinte.Mesp (Figure 5—figure supplement 1) and Ciinte.Mesp reporter construct (Figure 5E–G). These experiments revealed that both M. occidentalis Lhx3/4 proteins are conserved enough to activate low levels of Ciinte.Mesp expression (presumably by synergizing with endogenous Ciinte.Tbx6-r.b). However, neither was as effective as Ciinte.Lhx3/4 in activating Ciinte.Mesp (Figure 5H). These data suggested that cis/trans or trans/trans co-evolution involving the highly divergent Moocci.Lhx3/4.b paralog may only partially account for the incompatibility of Mesp cis-regulatory logic between the two species.10.7554/eLife.03728.021Figure 5.Divergence of Mesp regulation due to changes in cis and trans.

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