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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.Mesp in situ hybridization at tailbud stage.In situ hybridization for Moocci.Mesp in initial/early tailbud embryo, showing no expression at this stage. Image is a coronal view with anterior to the left.DOI:http://dx.doi.org/10.7554/eLife.03728.006
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fig1s3: Moocci.Mesp in situ hybridization at tailbud stage.In situ hybridization for Moocci.Mesp in initial/early tailbud embryo, showing no expression at this stage. Image is a coronal view with anterior to the left.DOI:http://dx.doi.org/10.7554/eLife.03728.006

Mentions: This faithful recapitulation of Moocci.Mesp expression and the persistence of GFP allows for visualization of the descendants of B7.5 long after endogenous Moocci.Mesp transcription has ceased (Figure 1—figure supplement 3; Davidson et al., 2005). At the tailbud stage, we find that each B7.5 blastomere gives rise to four grand-daughter cells (Figure 1E). The two anterior B7.5 grand-daughter cells on either side of the bilaterally symmetric embryo migrate anteriorly and are termed the trunk ventral cells (TVCs) due to their final position in the C. intestinalis and H. roretzi embryos (Nishida, 1987). Their posterior sister cells remain in the tail and become anterior tail muscles (ATMs). As far as we can tell, B7.5 lineage ontogeny is perfectly conserved between M. occidentalis and C. intestinalis (Figure 1F).


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.Mesp in situ hybridization at tailbud stage.In situ hybridization for Moocci.Mesp in initial/early tailbud embryo, showing no expression at this stage. Image is a coronal view with anterior to the left.DOI:http://dx.doi.org/10.7554/eLife.03728.006
© Copyright Policy
Related In: Results  -  Collection

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

fig1s3: Moocci.Mesp in situ hybridization at tailbud stage.In situ hybridization for Moocci.Mesp in initial/early tailbud embryo, showing no expression at this stage. Image is a coronal view with anterior to the left.DOI:http://dx.doi.org/10.7554/eLife.03728.006
Mentions: This faithful recapitulation of Moocci.Mesp expression and the persistence of GFP allows for visualization of the descendants of B7.5 long after endogenous Moocci.Mesp transcription has ceased (Figure 1—figure supplement 3; Davidson et al., 2005). At the tailbud stage, we find that each B7.5 blastomere gives rise to four grand-daughter cells (Figure 1E). The two anterior B7.5 grand-daughter cells on either side of the bilaterally symmetric embryo migrate anteriorly and are termed the trunk ventral cells (TVCs) due to their final position in the C. intestinalis and H. roretzi embryos (Nishida, 1987). Their posterior sister cells remain in the tail and become anterior tail muscles (ATMs). As far as we can tell, B7.5 lineage ontogeny is perfectly conserved between M. occidentalis and C. intestinalis (Figure 1F).

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