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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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Weak and leaky expression of Ciinte.Mesp reporter in M. occidentalis embryos.In situ hybridization for mCherry mRNA (green) in a M. occidentalis early gastrula stage embryo electroporated with Ciinte.Mesp>mCherry. Nuclei counterstained with DAPI (blue). Embryo is viewed vegetally, anterior to the top. Expression in B7.5 blastomeres (solid arrowheads) was observed in 42% of embryos. Ectopic expression in other B-line cells (hollow arrowhead) was seen in 24% of embryos. Ectopic expression in A-line neural precursors (hollow double arrowhead) was seen in 8% of embryos. In contrast, in situ hybridization revealed that Moocci.Mesp reporter construct is expressed in the TVCs in 60% of electroporated M. occidentalis embryos, with 0% embryos showing any ectopic reporter gene expression (data not shown, see Figure 1D for example). n = 50 embryos for each construct.DOI:http://dx.doi.org/10.7554/eLife.03728.018
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fig4s1: Weak and leaky expression of Ciinte.Mesp reporter in M. occidentalis embryos.In situ hybridization for mCherry mRNA (green) in a M. occidentalis early gastrula stage embryo electroporated with Ciinte.Mesp>mCherry. Nuclei counterstained with DAPI (blue). Embryo is viewed vegetally, anterior to the top. Expression in B7.5 blastomeres (solid arrowheads) was observed in 42% of embryos. Ectopic expression in other B-line cells (hollow arrowhead) was seen in 24% of embryos. Ectopic expression in A-line neural precursors (hollow double arrowhead) was seen in 8% of embryos. In contrast, in situ hybridization revealed that Moocci.Mesp reporter construct is expressed in the TVCs in 60% of electroporated M. occidentalis embryos, with 0% embryos showing any ectopic reporter gene expression (data not shown, see Figure 1D for example). n = 50 embryos for each construct.DOI:http://dx.doi.org/10.7554/eLife.03728.018

Mentions: Given the obvious parallels between C. intestinalis and M. occidentalis cardiopharyngeal development, we expected transcriptional regulatory mechanisms to also be highly conserved between the two species. We tested this assumption by electroporating C. intestinalis reporter constructs into M. occidentalis embryos, and vice-versa. We observed that a Ciinte.Mesp reporter construct (Davidson et al., 2005), when electroporated into M. occidentalis embryos, drives relatively weak reporter gene expression in B7.5 with substantial leaky expression in other tissues (Figure 4A, Figure 4—figure supplement 1). Conversely, the Moocci.Mesp enhancer fails to drive any reporter gene expression when electroporated into C. intestinalis embryos (Figure 4B), despite recapitulating robust B7.5-specific expression in M. occidentalis embryos (Figure 1D,E).10.7554/eLife.03728.017Figure 4.Developmental system drift of Mesp regulation between C. intestinalis and M. occidentalis.


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)

Weak and leaky expression of Ciinte.Mesp reporter in M. occidentalis embryos.In situ hybridization for mCherry mRNA (green) in a M. occidentalis early gastrula stage embryo electroporated with Ciinte.Mesp>mCherry. Nuclei counterstained with DAPI (blue). Embryo is viewed vegetally, anterior to the top. Expression in B7.5 blastomeres (solid arrowheads) was observed in 42% of embryos. Ectopic expression in other B-line cells (hollow arrowhead) was seen in 24% of embryos. Ectopic expression in A-line neural precursors (hollow double arrowhead) was seen in 8% of embryos. In contrast, in situ hybridization revealed that Moocci.Mesp reporter construct is expressed in the TVCs in 60% of electroporated M. occidentalis embryos, with 0% embryos showing any ectopic reporter gene expression (data not shown, see Figure 1D for example). n = 50 embryos for each construct.DOI:http://dx.doi.org/10.7554/eLife.03728.018
© Copyright Policy
Related In: Results  -  Collection

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

fig4s1: Weak and leaky expression of Ciinte.Mesp reporter in M. occidentalis embryos.In situ hybridization for mCherry mRNA (green) in a M. occidentalis early gastrula stage embryo electroporated with Ciinte.Mesp>mCherry. Nuclei counterstained with DAPI (blue). Embryo is viewed vegetally, anterior to the top. Expression in B7.5 blastomeres (solid arrowheads) was observed in 42% of embryos. Ectopic expression in other B-line cells (hollow arrowhead) was seen in 24% of embryos. Ectopic expression in A-line neural precursors (hollow double arrowhead) was seen in 8% of embryos. In contrast, in situ hybridization revealed that Moocci.Mesp reporter construct is expressed in the TVCs in 60% of electroporated M. occidentalis embryos, with 0% embryos showing any ectopic reporter gene expression (data not shown, see Figure 1D for example). n = 50 embryos for each construct.DOI:http://dx.doi.org/10.7554/eLife.03728.018
Mentions: Given the obvious parallels between C. intestinalis and M. occidentalis cardiopharyngeal development, we expected transcriptional regulatory mechanisms to also be highly conserved between the two species. We tested this assumption by electroporating C. intestinalis reporter constructs into M. occidentalis embryos, and vice-versa. We observed that a Ciinte.Mesp reporter construct (Davidson et al., 2005), when electroporated into M. occidentalis embryos, drives relatively weak reporter gene expression in B7.5 with substantial leaky expression in other tissues (Figure 4A, Figure 4—figure supplement 1). Conversely, the Moocci.Mesp enhancer fails to drive any reporter gene expression when electroporated into C. intestinalis embryos (Figure 4B), despite recapitulating robust B7.5-specific expression in M. occidentalis embryos (Figure 1D,E).10.7554/eLife.03728.017Figure 4.Developmental system drift of Mesp regulation between C. intestinalis and M. occidentalis.

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