Limits...
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.

Show MeSH

Related in: MedlinePlus

The B7.5 lineage of the tail-less species M. occulta.(A) In situ hybridization for M. occulta Mesp (Mooccu.Mesp) in 110-cell st/early gastrula embryo, showing expression (green) in the B7.5 blastomeres. Image is taken from a vegetal view, anterior to the top. (B) Lateral view of a transiently-transfected M. occulta mid-tailbud-equivalent stage embryo electroporated with a Moocul.Hand-r reporter construct (Moocul.Hand-r>H2B::GFP). The reporter proteins (Histone2B::GFP, green) label the cell nuclei descendant of the trunk ventral cells (TVCs), namely the secondary TVCs (STVCs) and the first heart precursors (FHPs). Due to leader/trailer mosaic retention of the electroporated plasmid (Stolfi and Christiaen, 2012), the daughters of the leader cell (‘leader STVC’ and ‘leader HFP’) are more strongly labeled than the daughters of the trailer cell. Some staining is also seen in what may be anterior endoderm or A7.6 mesoderm, other known territories of Hand-r expression in M. occulta and other ascidian species. Anterior is to the bottom left.DOI:http://dx.doi.org/10.7554/eLife.03728.005
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4356046&req=5

fig1s2: The B7.5 lineage of the tail-less species M. occulta.(A) In situ hybridization for M. occulta Mesp (Mooccu.Mesp) in 110-cell st/early gastrula embryo, showing expression (green) in the B7.5 blastomeres. Image is taken from a vegetal view, anterior to the top. (B) Lateral view of a transiently-transfected M. occulta mid-tailbud-equivalent stage embryo electroporated with a Moocul.Hand-r reporter construct (Moocul.Hand-r>H2B::GFP). The reporter proteins (Histone2B::GFP, green) label the cell nuclei descendant of the trunk ventral cells (TVCs), namely the secondary TVCs (STVCs) and the first heart precursors (FHPs). Due to leader/trailer mosaic retention of the electroporated plasmid (Stolfi and Christiaen, 2012), the daughters of the leader cell (‘leader STVC’ and ‘leader HFP’) are more strongly labeled than the daughters of the trailer cell. Some staining is also seen in what may be anterior endoderm or A7.6 mesoderm, other known territories of Hand-r expression in M. occulta and other ascidian species. Anterior is to the bottom left.DOI:http://dx.doi.org/10.7554/eLife.03728.005

Mentions: Ciinte.Mesp specifies the B7.5 cells as the sole progenitors of the cardiopharyngeal lineage (Satou et al., 2004; Davidson et al., 2005; Hirano and Nishida, 1997; Stolfi et al., 2010). We performed RNA in situ hybridization (ISH) for M. occidentalis Mesp (Moocci.Mesp) and found that this gene is also expressed only in the B7.5 cells of M. occidentalis embryos (Figure 1C). These cells are unequivocally identified due to the perfect conservation of early embryonic cell cleavage patterns in all ascidians. ISH for the M. occulta Mesp gene (Mooccu.Mesp) also revealed conserved expression in this tail-less species (Figure 1—figure supplement 2A).


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)

The B7.5 lineage of the tail-less species M. occulta.(A) In situ hybridization for M. occulta Mesp (Mooccu.Mesp) in 110-cell st/early gastrula embryo, showing expression (green) in the B7.5 blastomeres. Image is taken from a vegetal view, anterior to the top. (B) Lateral view of a transiently-transfected M. occulta mid-tailbud-equivalent stage embryo electroporated with a Moocul.Hand-r reporter construct (Moocul.Hand-r>H2B::GFP). The reporter proteins (Histone2B::GFP, green) label the cell nuclei descendant of the trunk ventral cells (TVCs), namely the secondary TVCs (STVCs) and the first heart precursors (FHPs). Due to leader/trailer mosaic retention of the electroporated plasmid (Stolfi and Christiaen, 2012), the daughters of the leader cell (‘leader STVC’ and ‘leader HFP’) are more strongly labeled than the daughters of the trailer cell. Some staining is also seen in what may be anterior endoderm or A7.6 mesoderm, other known territories of Hand-r expression in M. occulta and other ascidian species. Anterior is to the bottom left.DOI:http://dx.doi.org/10.7554/eLife.03728.005
© Copyright Policy
Related In: Results  -  Collection

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

fig1s2: The B7.5 lineage of the tail-less species M. occulta.(A) In situ hybridization for M. occulta Mesp (Mooccu.Mesp) in 110-cell st/early gastrula embryo, showing expression (green) in the B7.5 blastomeres. Image is taken from a vegetal view, anterior to the top. (B) Lateral view of a transiently-transfected M. occulta mid-tailbud-equivalent stage embryo electroporated with a Moocul.Hand-r reporter construct (Moocul.Hand-r>H2B::GFP). The reporter proteins (Histone2B::GFP, green) label the cell nuclei descendant of the trunk ventral cells (TVCs), namely the secondary TVCs (STVCs) and the first heart precursors (FHPs). Due to leader/trailer mosaic retention of the electroporated plasmid (Stolfi and Christiaen, 2012), the daughters of the leader cell (‘leader STVC’ and ‘leader HFP’) are more strongly labeled than the daughters of the trailer cell. Some staining is also seen in what may be anterior endoderm or A7.6 mesoderm, other known territories of Hand-r expression in M. occulta and other ascidian species. Anterior is to the bottom left.DOI:http://dx.doi.org/10.7554/eLife.03728.005
Mentions: Ciinte.Mesp specifies the B7.5 cells as the sole progenitors of the cardiopharyngeal lineage (Satou et al., 2004; Davidson et al., 2005; Hirano and Nishida, 1997; Stolfi et al., 2010). We performed RNA in situ hybridization (ISH) for M. occidentalis Mesp (Moocci.Mesp) and found that this gene is also expressed only in the B7.5 cells of M. occidentalis embryos (Figure 1C). These cells are unequivocally identified due to the perfect conservation of early embryonic cell cleavage patterns in all ascidians. ISH for the M. occulta Mesp gene (Mooccu.Mesp) also revealed conserved expression in this tail-less species (Figure 1—figure supplement 2A).

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