Conversion to Aniseed format of data from Yutaka Satou's gene expression profiles of transcription factors and signalling molecule ISH screen (Development. 2004 131:4047-58).

Original annotation :
Gene name :Mesp.
Expression pattern : No signal was detected.

Conversion to Aniseed format of data from Yutaka Satou's gene expression profiles of transcription factors and signalling molecule ISH screen (Development. 2004 131:4047-58).

Original annotation :
Gene name :Mesp.
Expression pattern : No distinct zygotic signal was detected.

Conversion to Aniseed format of data from Yutaka Satou's gene expression profiles of transcription factors and signalling molecule ISH screen (Development. 2004 131:4047-58).

Original annotation :
Gene name :Mesp.
Expression pattern : No distinct zygotic signal was detected.

Vegetal view of a 32-cell stage embryo electroporated with a lacZ transgene containing the -110 bp of the 5' flanking Ci-Mesp region (construct named Ci-110 in the paper). This construct contains three putative T-Box binding motifs. T-Box1 : AGGCGATAA; T-Box2 : CGGCGATAA; T-Box3 : TAGACACCT. Expression is transiently observed in the B6.4 blastomere.

Conversion to Aniseed format of data from Yutaka Satou's gene expression profiles of transcription factors and signalling molecule ISH screen (Development. 2004 131:4047-58).

Original annotation :
Gene name :Mesp.
Expression pattern : No distinct zygotic signal was detected.

Vegetal view of an early gastrula stage wild type embryo probed for Ci-Mesp expression.

Original Annotation :
Ci-Mesp was expressed in B7.5 cell pair.

Vegetal views of early gastrula stage wild type embryos probed for Ci-Mesp expression.

Original Annotation :
Ci-Mesp was expressed in B7.5 cell pair (white arrows).

Early gastrula stage embryos co-injected with indicated MOs and rhodamine-dextran and hybridized with the Mesp probe.

Original Annotation :
Lhx3a-ATG produce severe development defects: disorganized blastomeres may adhere more loosely to each other.

Vegetal and lateral views of early gastrula stage embryos co-injected with indicated MOs and rhodamine-dextran and hybridized with the Mesp probe.

Original Annotation :
Lhx3-E2I3 produces severe development defects: disorganized blastomeres may adhere more loosely to each other. Lhx3-E2I3 MO sometimes produces detachment of the endoderm precursors from the animal blastomere to which they normally adhere (lateral views). Note that the three morpholinos also produce severe morphological defects at later stages, presumably resulting from the failure of early endoderm specification.

Lateral views of early gastrula stage embryos co-injected with indicated MOs and rhodamine-dextran and hybridized with the Mesp probe.

Original Annotation :
Lhx3b-ATG MO sometimes produces detachment of the endoderm precursors from the animal blastomere to which they normally adhere (lateral views). Note that the three morpholinos also produce severe morphological defects at later stages, presumably resulting from the failure of early endoderm specification.

Fig 5.S1 A

Conversion to Aniseed format of data from Yutaka Satou's gene expression profiles of transcription factors and signalling molecule ISH screen (Development. 2004 131:4047-58).

Original annotation :
Gene name :Mesp.
Expression pattern : B7.5

Control experiment not described in the paper. Entry deduced from the article and from others ANISEED data.

Early gastrula embryos electroporated with a construct containing region -150bp/39bp upstream Ci-Mesp.
This construct drives spontaneous ectopic expression in B7.7 (open arrowheads) and B8.5 (solid arrowheads) mesenchyme precursors. Arrows point to the B7.5 cells.
The scheme represents the cis regulatory region and the different regulatory motifs Tbx6b/c sites in blue and Lhx3 sites in green.
The graph presents the proportion of embryos showing reporter gene activity in indicated tissues (n = number of embryos scored).

Early gastrula embryos electroporated with a construct containing region -150bp/39bp upstream Ci-Mesp (arrows point to the B7.5 cells). The scheme represents the cis regulatory region and the different regulatory motifs Tbx6b/c sites in blue and Lhx3 sites in green.
The graph presents the proportion of embryos showing reporter gene activity in indicated tissues (n = number of embryos scored).

Early gastrula embryos electroporated with a construct containing region -150bp/39bp upstream Ci-Mesp.
The scheme represents the cis regulatory region and the different regulatory motifs Tbx6b/c sites in blue and Lhx3 sites in green. The first Lhx3 site is mutated.
The graph presents the proportion of embryos showing reporter gene activity in indicated tissues (n = number of embryos scored).

This deletion is not sufficient to abolish Ci-Mesp expression in B7.5 cells (60% of embryos or in B line muscles and mesenchyme (for 20% of embryos).

Early gastrula embryos electroporated with a construct containing region -150bp/39bp upstream Ci-Mesp.
The scheme represents the cis regulatory region and the different regulatory motifs Tbx6b/c sites in blue and Lhx3 sites in green. The second Lhx3 site is mutated.
The graph presents the proportion of embryos showing reporter gene activity in indicated tissues (n = number of embryos scored).

This deletion is sufficient to abolish Ci-Mesp expression in B7.5 cells (expressed only in for 30% of embryos) but not in B line muscles and mesenchyme (for 30% of embryos).

Early gastrula embryos electroporated with a construct containing region -150bp/39bp upstream Ci-Mesp.
The scheme represents the cis regulatory region and the different regulatory motifs Tbx6b/c sites in blue and Lhx3 sites in green. The third Lhx3 site is mutated.
The graph presents the proportion of embryos showing reporter gene activity in indicated tissues (n = number of embryos scored).

This deletion is sufficient to abolish Ci-Mesp expression in B7.5 cells (black arrows) (expressed only in 10% of embryos) but not in B line muscles and mesenchyme arrowheads (for 30% of embryos) (open arrowheads : B8.5 ; solid arrowhead : B7.7).

Early gastrula embryos electroporated with a construct containing region -150bp/39bp upstream Ci-Mesp.
The scheme represents the cis regulatory region and the different regulatory motifs Tbx6b/c sites in blue and Lhx3 sites in green. The fouth and fifth Lhx3 sites are mutated.
The graph presents the proportion of embryos showing reporter gene activity in indicated tissues (n = number of embryos scored).

This deletion is not sufficient to abolish Ci-Mesp expression in B7.5 cells (for 60% of embryos).

Early gastrula embryos electroporated with a construct containing region -150bp/39bp upstream Ci-Mesp.
The scheme represents the cis regulatory region and the different regulatory motifs Tbx6b/c sites in blue and Lhx3 sites in green. The sixth Lhx3 site is mutated.
The graph presents the proportion of embryos showing reporter gene activity in indicated tissues (n = number of embryos scored).

This deletion is not sufficient to abolish Ci-Mesp expression in B7.5 cells (for 60% of embryos) and in B line muscles and mesenchyme (for 35% of embryos).

Vegetal view of a 110-cell stage embryo electroporated with a lacZ transgene containing the -110 +39 bp of the 5' flanking Ci-Mesp region (construct named Ci-110 in the paper). And co-hybridized with probes against Tbx6c (blue) and lacZ mRNAs (red). Nuclear staining by the lacZ probe indicates nascent transcripts, whereas Tbx6c transcripts are detected in the cytoplasm owing to an earlier onset of expression.

Immunodetection of β-gal expression (green) in B7.5 cells in a gastrulating Ciona robusta embryo transfected with MesP>lacZ transgene, vegetal view.
Scale bar: 50 μm.

Vegetal view of a mid-gastrula stage embryo electroporated with a lacZ transgene containing the -110 bp of the 5' flanking Ci-Mesp region (construct named Ci-110 in the paper). This construct contains three putative T-Box binding motifs. T-Box1 : AGGCGATAA; T-Box2 : CGGCGATAA; T-Box3 : TAGACACCT. Expression is observed in the B7.5 cell pair.

Ventral view of a late-gastrula stage embryo electroporated with a lacZ transgene containing the -110 bp of the 5' flanking Ci-Mesp region (construct named Ci-110 in the paper). This construct contains three putative T-Box binding motifs. T-Box1 : AGGCGATAA; T-Box2 : CGGCGATAA; T-Box3 : TAGACACCT. The B7.5 lineage cells have now involuted to the ventral side, soon after this stage Mesp expression becomes undetectable.

Conversion to Aniseed format of data from Yutaka Satou's gene expression profiles of transcription factors and signalling molecule ISH screen (Development. 2004 131:4047-58).

Original annotation :
Gene name :Mesp.
Expression pattern : muscle, mesenchyme.
Comment : descendants of B7.5

Ventral view of a WT Ciona robusta late gastrula stage embryo electroporated with Mesp>RFP reporter construct and counterstained with autofluorescent myoplasm (green) and phalloidin (blue). RFP staining is observed in B8.9 and B8.10 cell pairs.
Original annotation: Arrowheads indicate B7.5 lineage cells prior to the asymmetric cell division.
Time of fixation is indicated in hours post-fertilization at 19°C.

Late gastrula stage Mesp-GFP transgenic Ciona robusta embryo stained with rabbit anti-GFP (red) and mouse anti-dpERK (green). Mesp reporter construct labels B7.5 lineage. dpERK is detected in epidermis an in trunk ventral cells precursors.
Original annotation: Purple arrows indicate heart precursor cells showing nuclear staining for dpERK, white arrows indicate tail muscle precursors, and arrowheads indicate B7.5 lineage cells just prior to the asymmetric division.

Conversion to Aniseed format of data from Yutaka Satou's gene expression profiles of transcription factors and signalling molecule ISH screen (Development. 2004 131:4047-58).

Original annotation :
Gene name :Mesp.
Expression pattern : No distinct zygotic signal was detected.

Ventral view of a WT Ciona robusta mid neurula stage embryo electroporated with Mesp>RFP reporter construct and counterstained with autofluorescent myoplasm (green) and phalloidin (blue). Mesp cis-regulatory sequence drives RFP expression in the B7.5 lineage.
Original annotation: Arrowheads indicate B7.5 lineage cells prior to the asymmetric cell division, white arrows indicate myoplasm containing tail muscle lineage cells, and purple arrows indicate heart precursor cells
Time of fixation is indicated in hours post-fertilization at 19°C.

Late neurula embryo electroporated with Mesp > lacZ (red) and hybridized with a Bmp2/4 antisense RNA probe (green). Scale bars 20 μm.

Original annotation:
At this stage, Bmp2/4 is not expressed in TVCs (arrowheads), but in the adjacent ventral epidermis.

Lateral view of a initial tailbud stage embryo electroporated with a GFP transgene containing the -110 bp of the 5' flanking Ci-Mesp region (construct named Ci-110 in the paper). This construct contains three putative T-Box binding motifs. expression is detected in the whole B7.5 lineage (muscle and TVC).

Lateral view of a WT Ciona robusta initial tailbud stage embryo electroporated with Mesp>RFP reporter construct and counterstained with autofluorescent myoplasm (green) and phalloidin (blue).
Original annotation: White arrows indicate myoplasm containing tail muscle lineage cells, and purple arrows indicate heart precursor cells.
Time of fixation is indicated in hours post-fertilization at 19°C.

Conversion to Aniseed format of data from Yutaka Satou's gene expression profiles of transcription factors and signalling molecule ISH screen (Development. 2004 131:4047-58).

Original annotation :
Gene name :Mesp.
Expression pattern : No distinct zygotic signal was detected.

Early-tailbud embryos electroporated with Mesp > lacZ, detected by immunofluorescence (red), and hybridized with the NK4 antisense RNA probes (green).

Original annotation:
They observed conspicuous TVC specific expression of GATAa and Tolloid, while NK4 and Bmp2/4 expression could not be detected above background levels.

Early-tailbud embryos electroporated with Mesp > lacZ, detected by immunofluorescence (red), and hybridized with the Bmp2/4 antisense RNA probes (green).

Expression in the B7.5 cells lineage (anterior tail muscle and trunk ventral cells).

Early-tailbud embryos electroporated with Mesp > lacZ, detected by immunofluorescence (red), and hybridized with the GATAa antisense RNA probes (green).

Original annotation:
They observed conspicuous TVC specific expression of GATAa and Tolloid.

Early-tailbud embryos electroporated with Mesp > lacZ, detected by immunofluorescence (red), and hybridized with the Tolloid antisense RNA probes (green).

Original annotation:
As expected, we observed conspicuous TVC specific expression of GATAa and Tolloid.

Lateral view of an early tailbud stage embryo (15hpf) electroporated with a GFP transgene containing the -110 +39 bp flanking Ci-Mesp region (construct named Ci-110 in the paper). This construct contains three putative T-Box binding motifs. Expression is detected in the whole B7.5 lineage (muscle and TVC).

Lateral view of an early tailbud stage embryo (14 hpf) electroporated with a GFP transgene containing the -110 +39 bp flanking Ci-Mesp region (construct named Ci-110 in the paper). This construct contains three putative T-Box binding motifs. expression is detected in the whole B7.5 lineage (muscle and TVC).

(Data not shown in the article)
Mesp enhancer drives GFP expression in the B7.5 lineage in WT Ciona robusta early tailbud embryos.

Experimental conditions description : (Data not shown in the article).
miR-1 enhancer drives LacZ expression specificaly in the tail muscle lineage of WT Ciona robusta early tailbud embryos.

Dorsal view (anterior to the left) of a Ciona robusta embryo co-electroporated with Mesp>GFP (green) and miR-1>LacZ (black nuclei), treated with cytochalasin at the 110-cell stage and fixed at 10hpf, and treated with DMSO (control) at the 16-cell stage.
Mesp drives GFP expression in the B7.5 lineage.

Dorsal view (anterior to the left) of a Ciona robusta embryo co-electroporated with Mesp>GFP (green) and miR-1>LacZ (black nuclei), treated with cytochalasin at the 110-cell stage and fixed at 10hpf, and treated with DMSO (control) at the 16-cell stage.
miR-1 enhancer drives LacZ expression in the tail muscle lineage.

Conversion to Aniseed format of data from Yutaka Satou's gene expression profiles of transcription factors and signalling molecule ISH screen (Development. 2004 131:4047-58).

Original annotation :
Gene name :Mesp.
Expression pattern : No distinct zygotic signal was detected.

Close-up views of the tail-trunk boundary of mid-tailbud embryos electroporated with Mesp>GFP. GFP was detected by immunohistochemistry.
Blue staining : phalloidin staining.

Mid-tailbud embryo electroporated with Mesp > lacZ (red) and hybridized with a Bmp2/4 antisense RNA probe (green).
(L) leader and (T) trailer TVCs (arrowheads) ; ATMs (anterior tail muscle) (arrows).

Expression of the construct Mesp > lacZ in B7.5 lineage (TVCs and anterior tail muscle).

No picture available in the paper. The -138 to +39 mesp enhancer placed in front of the fkh promoter (construct named Ci-138 in the paper) drives expression in the whole B7.5 lineage.

This enhancer, in which T-box site B is mutated (construct named Ci-B Mut-2 in the paper), still drives expression in the B7.5 line, but with much lower efficiency than the parental -138 +39 mesp enhancer. No picture provided.

Lateral view of a mid-tailbud stage embryo electroporated with a lacZ transgene containing the -110 bp of the 5' flanking Ci-Mesp region (construct named Ci-110 in the paper). This construct contains three putative T-Box binding motifs. T-Box1 : AGGCGATAA; T-Box2 : CGGCGATAA; T-Box3 : TAGACACCT. Expression is observed in the anterior tail muscles and the trunk ventral cells.

Embryos electroporated with a mutated mesp minimal region placed in front of fkh basal promoter driving LacZ (construct named Ci-B Mut-1 in the paper). Point mutation of T-box site B leads to the loss of activity of the minimal mesp enhancer. No picture available in the paper.

Embryos electroporated with a mutated mesp minimal region placed in front of fkh basal promoter driving LacZ (construct named Ci-B Mut-2 in the paper). Point mutation of T-box site B leads to the loss of activity of the minimal mesp enhancer. No picture available in the paper.

Embryos electroporated with a mutated mesp minimal region placed in front of fkh basal promoter driving LacZ (construct named Ci-B-Mut-T in the paper). This mutated minimal mesp enhancer drives expression in all B-7.5 progeny. No picture provided.

Lateral view of a mid-tailbud stage embryo electroporated with a lacZ transgene containing the -107 bp to +39bp of the 5' flanking Ci-Mesp region (construct named Ci-107 in the paper). The T-Box1 of the -110bp to +39bp is partially deleted. Expression is lost in the anterior tail muscles and the trunk ventral cells.

Lateral view of a WT Ciona robusta mid tailbud stage embryo electroporated with Mesp>RFP reporter construct and counterstained with autofluorescent myoplasm (green) and phalloidin (blue). RFP staining is observed in B7.5 lineage
Original annotation: White arrows indicate myoplasm containing tail muscle lineage cells, and purple arrows indicate heart precursor cells
Time of fixation is indicated in hours post-fertilization at 19°C.

(Data not shown in the article)
At the tailbud stage, in WT conditions, Mesp enhancer drives reporter activity in the B7.5 lineage of Ciona robusta embryos.

(Data not shown in the article)
At the tailbud stage, in WT conditions, FoxF enhancer drives reporter activity in th trunk ventral cells and the head epidermis of Ciona robusta embryos.

Ventral view of a Ciona robusta midtailbud-stage embryo electroporated once with MesP>GFP (green), rinsed, and electroporated with MesP>RFP (red). The second image is the un-annotated HD picture.
Original annotation: Due to mosaicism, this individual is expressing MesP>GFP only in cells of the right hemisphere, and MesP>RFP only in cells of the left hemisphere.
Image is a composite of images taken at different focal planes of the same embryo. The seam between the two focal planes is indicated by the dashed line. Migratory heart precursors are labeled in the left panel, while tail muscles are labeled in the right panel. Both are descended from the B7.5 pair of blastomeres, which express MesP.

Ventral view of a Ciona robusta midtailbud-stage embryo electroporated once with MesP>GFP (green), rinsed, and electroporated with MesP>RFP (red). The second image is the un-annotated HD picture.
Original annotation: Due to mosaicism, this individual is expressing MesP>GFP only in cells of the right hemisphere, and MesP>RFP only in cells of the left hemisphere.
Image is a composite of images taken at different focal planes of the same embryo. The seam between the two focal planes is indicated by the dashed line. Migratory heart precursors are labeled in the left panel, while tail muscles are labeled in the right panel. Both are descended from the B7.5 pair of blastomeres, which express MesP.

Ventral view of a Ciona robusta midtailbud-stage embryo electroporated once with MesP>GFP (green), rinsed, and electroporated with MesP>RFP (red). The second image is the un-annotated HD picture.
Original annotation: Due to mosaicism, this individual is expressing MesP>GFP only in cells of the right hemisphere, and MesP>RFP only in cells of the left hemisphere.
Image is a composite of images taken at different focal planes of the same embryo. The seam between the two focal planes is indicated by the dashed line. Migratory heart precursors are labeled in the left panel, while tail muscles are labeled in the right panel. Both are descended from the B7.5 pair of blastomeres, which express MesP.

Ventral view of a Ciona robusta midtailbud-stage embryo electroporated once with MesP>GFP (green), rinsed, and electroporated with MesP>RFP (red). The second image is the un-annotated HD picture.
Original annotation: Due to mosaicism, this individual is expressing MesP>GFP only in cells of the right hemisphere, and MesP>RFP only in cells of the left hemisphere.
Image is a composite of images taken at different focal planes of the same embryo. The seam between the two focal planes is indicated by the dashed line. Migratory heart precursors are labeled in the left panel, while tail muscles are labeled in the right panel. Both are descended from the B7.5 pair of blastomeres, which express MesP.

Dorsal confocal projections (Anterior to the left) of a Ciona robusta embryo electroporated with Mesp>GFP (green) and FoxF>RFP (red), arrested at the 110-cell stage (4hpf) through treatment with cytochalasin and fixed at 10hpf. Mesp reporter drives GFP expression in the B7.5 lineage.

Dorsal confocal projections (Anterior to the left) of a Ciona robusta embryo electroporated with Mesp>GFP (green) and FoxF>RFP (red), arrested at the 110-cell stage (4hpf) through treatment with cytochalasin and fixed at 10hpf. The FoxF enhancer drives some reporter expression in the epidermis (faint red staining) and strong expression in the B7.5 lineage.
Original annotation: Treatment of 4H embryos with cytochalasin causes a block in the division of the B7.5 blastomeres at the 110-cell stage. Despite this block, FoxF reporter gene expression is observed in the B7.5 cells “on schedule,” ∼10 h after fertilization at the equivalent of the tailbud stage.

Lateral view of a late-tailbud stage embryo electroporated with a LacZ transgene containing the -110 bp of the 5' flanking Ci-Mesp region (construct named Ci-110 in the paper).

Lateral view of a late tailbud embryo electroporated with a GFP transgene containing the -110 bp of the 5' flanking Ci-Mesp region (construct named Ci-110 in the paper). This construct contains three putative T-Box binding motifs. Expression is observed in the trunk ventral cells and in the anterior ventral primary muscle cells.

Lateral view of a Ciona robusta late tailbud embryo transfected with MesP>lacZ (red) and FoxF[TVCenhancer]>H2B::mCherry (red) transgenes.
Mesp enhancer is active in B7.5 progeny and FoxF[TVCenhancer] drives mCherry expression in the trunk ventral cells.
Scale bar: 50 μm.

Lateral view of a Ciona robusta late tailbud embryo transfected with MesP>lacZ (red) and FoxF[TVCenhancer]>H2B::mCherry (red) transgenes.
Mesp enhancer is active in B7.5 progeny and FoxF[TVCenhancer] drives mCherry expression in the trunk ventral cells (white arrowheads).
Scale bar: 50 μm.

Ventral projection of a WT Ciona robusta late tailbud embryo electroporated with Mesp>H2B:GFP reporter construct.
Mesp enhancer drives GFP in the B7.5 lineage, including heart cell precursors and primary muscle lineage
Original comment: Heart progenitor nuclei are shown at high gain in the bottom right and demarcated by white arrowheads. Anterior tail muscle (ATM) cells are marked using yellow asterisks.
At St. 24, the head trunk region is roughly symmetric and the heart progenitor cells are symmetrically distributed along either side of the midline endostyle.

Ventral projection from confocal time-lapse analysis of a Ciona robusta late tailbud stage embryo where heart progenitor membranes are labeled by Mesp>GPI:GFP reporter construct.

Ventral view of the head of a WT Ciona robusta late tailbud stage embryo electroporated with Mesp>LacZ reporter construct. LacZ staining is observed in B7.5 lineage.

Ventral view of the head of a WTCiona robusta tadpole electroporated with Mesp>GFP reporter construct. GFP is observed in the B7.5 lineage.
Original annotation: In wild-type embryos, heart precursor cells migrate to the ventral midline and undergo a characteristic asymmetric cell division.

Ventral view of the head of a Ciona robusta late tailbud stage embryo co-electroporated with Mesp>GFP (green) and FoxF>RFP (red) reporter constructs. Mesp enhancers drives GFP staining in B7.5 lineage.
(D) Green channel.
(D') Red channel.(D'') Red and green channels.

Ventral view of the head of a Ciona robusta late tailbud stage embryo co-electroporated with Mesp>GFP (green) and FoxF>RFP (red) reporter constructs. FoxF enhancers drives GFP staining in the trunk ventral cells and in epidermis.
(D) Green channel.
(D') Red channel.(D'') Red and green channels.

Ventral projection of a WT Ciona robusta late tailbud embryo electroporated with Mesp>H2B:GFP reporter construct.
Mesp enhancer drives GFP in the B7.5 lineage, including heart cell precursors and primary muscle lineage
Original comment: Heart progenitor nuclei are shown at high gain in the bottom right and demarcated by white arrowheads. Anterior tail muscle (ATM) cells are marked using yellow asterisks.
By the development tal stade 25, the trunk region displays laterally asymmetric lobes. This overall morphological asymmetry is associated with a lateral shift of the heart progenitor cells to one side of the endostyle.

Lateral view of early tailbud stage embryos electroporated with a GFP transgene containing the -110 +39 bp flanking Ci-Mesp region (construct named Ci-110 in the paper). This construct contains three putative T-Box binding motifs. expression is detected in the whole B7.5 lineage (muscle and TVC).

Ventral projection from confocal time-lapse analysis of a Ciona robusta larva where heart progenitor membranes are labeled by Mesp>GPI:GFP reporter construct.

Lateral view of the head of a Ciona robusta tadpole electroporated with MesP>Histone2B(H2B)∷GFP (green).
The fusion protein is expressed in the B7.5 progeny.

Lateral view of the head of a Ciona robusta hatching larva transfected with MesP>H2B::mCherry (red nuclei) and mesP>PH::GFP (green) reporter constructs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors, that begin to encircle the siphon primordium.

Lateral view of the head of a Ciona robusta hatching larva transfected with MesP>H2B::mCherry (red nuclei) and mesP>PH::GFP (green) reporter constructs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors, that begin to encircle the siphon primordium.

Lateral view of the head of a Ciona robusta hatching larva transfected with MesP>H2B::mCherry (red nuclei) and mesP>PH::GFP (green) reporter constructs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors, that begin to encircle the siphon primordium.

Lateral view of the head of a Ciona robusta hatching larva transfected with MesP>H2B::mCherry (red nuclei) and mesP>PH::GFP (green) reporter constructs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors, that begin to encircle the siphon primordium.

Dorsal view of electroporated Ciona robusta larva exhibiting mosaic incorporation (left side) of Islet>GFP (green) and MesP>H2B∷mCherry (red) transgenes at 20 hpf, before the migration of the lateral TVCs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors. Islet>GFP expression is restricted to lateral TVCs. Dotted line indicates midline; M and L indicate medial and lateral, respectively.

Dorsal view of electroporated Ciona robusta larva exhibiting mosaic incorporation (left side) of Islet>GFP (green) and MesP>H2B∷mCherry (red) transgenes at 20 hpf, before the migration of the lateral TVCs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors. Islet>GFP expression is restricted to lateral TVCs. Dotted line indicates midline; M and L indicate medial and lateral, respectively.

Lateral view of the head of a Ciona robusta larva transfected with MesP>H2B::mCherry (red nuclei) and Islect>GFP (green) reporter constructs, and FoxF[TVC]>LacZ as a control.
Mesp enhancer is active in B7.5 lineage, [ie. heart primordium (arrowhead) and atrial siphon muscle (ASM) precursors (arrow)], and Islet enhancer in atrial ASM precursors and in the visceral ganglion.

Lateral view of the head of a Ciona robusta larva transfected with MesP>H2B::mCherry (red nuclei) and Islect>GFP (green) reporter constructs, and FoxF[TVC]>LacZ as a control.
Mesp enhancer is active in B7.5 lineage, [ie. heart primordium (arrowhead) and atrial siphon muscle (ASM) precursors (arrow)], and Islet enhancer in atrial ASM precursors and in the visceral ganglion.

Ventral projection from confocal time-lapse analysis of the head of a Ciona robusta larva where heart progenitor membranes are labeled by Mesp>GPI:GFP reporter construct.
Original comment: In Stage 27 larvae, protrusive activity was sometimes observed in lateral heart progenitor cells.

Ventral projection of a WT Ciona robusta swimming larva electroporated with Mesp>H2B:GFP reporter construct.
Mesp enhancer drives GFP in the B7.5 lineage, including heart cell precursors and primary muscle lineage.
Original comment: Heart progenitor nuclei are shown at high gain in the bottom right and demarcated by white arrowheads. Atrial siphon muscle precursors (ASM) are circled in red, and anterior tail muscle (ATM) cells are marked using yellow asterisks.
During St. 29, the head elongates and the papillae mature, priming larvae for settlement. The heart progenitor pool has divided to produce a medial group of heart precursor cells and is fanked by two lateral clusters of atrial siphon muscle (ASM) precursors. In these late larvae, cardiac laterality is more evident as the heart precursors have shifted completely of the endostyle-demarcated midline.

Lateral view of the head of a Ciona robusta hatching larva transfected with MesP>H2B::mCherry (red nuclei) and mesP>PH::GFP (green) reporter constructs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors, that encircle the siphon primordium.

Lateral view of the head of a Ciona robusta hatching larva transfected with MesP>H2B::mCherry (red nuclei) and mesP>PH::GFP (green) reporter constructs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors, that encircle the siphon primordium.

Lateral view of the head of a Ciona robusta hatching larva transfected with MesP>H2B::mCherry (red nuclei) and mesP>PH::GFP (green) reporter constructs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors, that encircle the siphon primordium.

Lateral view of the head of a Ciona robusta hatching larva transfected with MesP>H2B::mCherry (red nuclei) and mesP>PH::GFP (green) reporter constructs.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors, that encircle the siphon primordium.

Lateral view of a Ciona robusta larva electroporated with Islet>GFP (green) and MesP>H2B∷mCherry (red) transgenes at 24hpf, after migration of Islet>GFP-positive lateral TVC descendants around the atrial siphon primordium.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors. Islet>GFP expression is restricted to lateral TVCs. D and V indicate dorsal and ventral, respectively.

Lateral view of a Ciona robusta larva electroporated with Islet>GFP (green) and MesP>H2B∷mCherry (red) transgenes at 24hpf, after migration of Islet>GFP-positive lateral TVC descendants around the atrial siphon primordium.
Mesp enhancer is active in anterior tail muscles (asterisk) and in atrial siphon muscles precursors. Islet>GFP expression is restricted to lateral TVCs. D and V indicate dorsal and ventral, respectively.

Ventral projection of a Ciona robusta Stage 31 larva, where heart founder lineage cells are demarcated by Mesp > H2B:GFP (green), including heart precursors (HP) and atrial siphon muscle precursors (ASM). This control embryo was treated with DMSO and stained with phalloidin to visualize epidermal structures.

Original comment: Visualization of MesP>H2B∷CFP (green) in a juvenile [~100 hours post-fertilization (hpf)]. Expression is visible in the heart (arrowhead), atrial siphon muscles (ASMs), and longitudinal muscles (LoMs) (arrows). MesP is activated only in the B7.5 pair of cells at the gastrula stage. a.s., atrial siphon; o.s., oral siphon.

Magnified view of longitudinal muscles (LoMs, arrowhead) segregating from atrial siphon muscles (ASMs, arrows) during metamorphosis, visualized by MesP>lacZ expression (red) and in situ hybridization of Tbx1/10 (green). Panel width is ~100 μm.
(D) Mesp>LacZ expression
(E) In situ hybridization of Tbx1/10 (green).
(F) Merged view of (D) and (E), showing activation of Tbx1/10 in LoMs.

MesP>lacZ (Bgalactosidase immunofluorescence) stains B7.5 descendants in atrial siphon (AS), longitudinal muscles (LoM) heart (Ht), and reabsorbed tail (asterisk) of Ciona robusta 63hpf juveniles.

Ciona robusta juvenile (~100 hpf) raised from embryo transfected with Islet>H2B∷mCherry (B, red) and Mesp>LacZ (A, red).C is the merge image.
H2B::mCherry is observed in atrial siphon muscles and longitudinal muscles, but not heart.
Differentiated B7.5 descendants (heart, atrial siphon muscles, and longitudinal muscles) are visualized using Mesp>LacZ staining (red).
Original comment: . Insets c’ and c’’ are magnified views of corresponding dashed line boxes. Note co-localization of βgal immunostain and H2B::mCherry around atrial siphons (c’) but not in the heart (c’’). Asterisks denote βgal+, H2B::mCherry+ nuclei of longitudinal muscles in which βgal was obscured in the merged image. Arrow in c’’ show Islet+ cells of unknown origin in the endostyle. Islet>H2B::mCherry is also seen in the re-absorbed tail (t). Juvenile was counterstained by phallacidin:BODIPY FL conjugate.

Ciona robusta juvenile (~100 hpf) raised from embryo transfected with Islet>H2B∷mCherry (B, red) and Mesp>LacZ (A, red).C is the merge image.
H2B::mCherry is observed in atrial siphon muscles and longitudinal muscles, but not heart.
Differentiated B7.5 descendants (heart, atrial siphon muscles, and longitudinal muscles) are visualized using Mesp>LacZ staining (red).
Original comment: Insets c’ and c’’ are magnified views of corresponding dashed line boxes. Note co-localization of βgal immunostain and H2B::mCherry around atrial siphons (c’) but not in the heart (c’’). Asterisks denote βgal+, H2B::mCherry+ nuclei of longitudinal muscles in which βgal was obscured in the merged image. Arrow in c’’ show Islet+ cells of unknown origin in the endostyle. Islet>H2B::mCherry is also seen in the re-absorbed tail (t). Juvenile was counterstained by phallacidin:BODIPY FL conjugate.

Ciona robusta juveniles raised from embryos transfected with MesP>H2B∷mCherry (red), counterstained with phallacidin (blue-green). H2B∷mCherry+ B7.5 descendants populate the heart (Ht) and atrial siphon muscles (ASMs, arrows). Residual larval muscle staining is indicated by asterisk.