Endocardial identity is established during early somitogenesis by Bmp signalling acting upstream of npas4l and etv2
Ontology highlight
ABSTRACT: The endocardium plays important roles in the development and function of the vertebrate heart; however, few molecular markers of this tissue have been identified and little is known about what regulates its differentiation. Here, we describe the Gt(SAGFF27C); Tg(4xUAS:egfp) line as a marker of endocardial development in zebrafish. Transcriptomic comparison between endocardium and pan-endothelium confirms molecular distinction between these populations and time-course analysis suggests differentiation as early as eight somites. To investigate what regulates endocardial identity, we employed npas4l, etv2 and scl loss-of-function models. Endocardial expression is lost in npas4l mutants, significantly reduced in etv2 mutants and only modestly affected upon scl loss-of-function. Bmp signalling was also examined: overactivation of Bmp signalling increased endocardial expression, whereas Bmp inhibition decreased expression. Finally, epistasis experiments showed that overactivation of Bmp signalling was incapable of restoring endocardial expression in etv2 mutants. By contrast, overexpression of either npas4l or etv2 was sufficient to rescue endocardial expression upon Bmp inhibition. Together, these results describe the differentiation of the endocardium, distinct from vasculature, and place npas4l and etv2 downstream of Bmp signalling in regulating its differentiation.
Project description:The zebrafish heart remarkably regenerates after a severe ventricular damage followed by inflammation, fibrotic tissue deposition and removal concomitant with cardiac muscle replacement. We have investigated the role of the endocardium in this regeneration process. 3D-whole mount imaging in injured hearts revealed that GFP-labelled endocardial cells in ET33mi-60A transgenic fish become rapidly activated and highly proliferative at 3 days post cryoinjury (dpci). Endocardial cells extensively expand within the injury site and organize to form a coherent structure at 9 dpci that persists throughout the regeneration process. Upon injury, endocardial cells strongly up-regulate the Notch pathway ligand delta like4 (dll4) and the Notch receptors notch1b, notch2 and notch3. Expression profiling showed that Notch signalling inhibition affects endocardial gene expression and genes related to extracellular matrix remodelling and inflammation. Gain- and loss-of-function experiments revealed that Notch is required for the organization of the endocardium, attenuation of the inflammatory response and cardiomyocyte proliferation. These results demonstrate a novel structural and signalling role for the endocardium during heart regeneration.
Project description:The endocardium interacts with the myocardium to promote proliferation and morphogenesis during the later stages of heart development. However, the role of the endocardium in early cardiac ontogeny remains under-explored. Given the shared origin, subsequent juxtaposition, and essential cell-cell interactions of endocardial and myocardial cells throughout heart development, we hypothesized that paracrine signaling from the endocardium to the myocardium is critical for initiating early differentiation of myocardial cells. To test this, we generated an in vitro, endocardial-specific ablation model using the diphtheria toxin receptor under the regulatory elements of the NFATc1 genomic locus (NFATc1-DTR) Early treatment of NFATc1-DTR embryoid bodies with diphtheria toxin efficiently ablated endocardial cells, which significantly attenuated the percent of beating EBs in culture and expression of early and late myocardial differentiation markers. The addition of Bmp2 during endocardial ablation partially rescued myocyte differentiation, maturation and function. Therefore, we conclude that early stages of myocardial differentiation rely on endocardial paracrine signaling mediated in part by Bmp2. Our findings provide novel insight into early endocardial-myocardial interactions that can be explored to promote early myocardial development and growth.
Project description:Embryonic cells including endothelial progenitors undergo extensive migration and differentiation events; however, whether and how these processes are interrelated remains unclear. The transcription factor Npas4l is necessary for endothelial specification in zebrafish by inducing the expression of the transcription factor genes etsrp, tal1 and lmo2. We generated a knock-in reporter in the npas4l locus to visualize endothelial progenitors and their derivatives in wild-type and mutant embryos. We find that in npas4l mutants, npas4l reporter expressing cells do not migrate to the midline and instead contribute to skeletal muscle and pronephric tubules. Investigating the Npas4l transcriptional effectors, we find that npas4l reporter expressing cells in tal1 mutants fail to migrate while those in etsrp mutants migrate but fail to differentiate. In lmo2 mutants, npas4l reporter expressing cells migrate and differentiate, but many express pronephric tubule markers. Altogether, these data reveal the complex regulation of endothelial progenitor migration, differentiation and fate restriction.
Project description:To investigate roles for Tbx20 in endocardium, we ablated Tbx20 utilizing Tie2Cre. Tie2Cre;Tbx20 mutants died at E14, exhibiting defects in multiple aspects of cardiac septation. Although endocardial cells lacking Tbx20 were able to undergo endothelial-to-mesenchymal transition, cushion mesenchymal cells lacking Tbx20 did not disperse normally. Non-cell autonomous roles of endocardial Tbx20 were also revealed, as evidenced by decreased myocardialization of outflow tract and failure of dorsal mesenchymal protrusion formation in mutants. To examine how ablation of Tbx20 in endocardial lineages affected gene expression, we performed global gene expression analysis on purified endocardial lineages. E12.5 hearts were dissociated, and Tie2Cre;RosatdTom lineage traced cells of controls and mutants were isolated by fluorescence activated cell sorting (FACS), after exclusion of blood cells (Ter119+, CD41+ and/or CD45+). Mutant endocardial lineages exhibited decreased expression of genes associated with extracellular matrix and cell migration. E12.5 hearts were dissociated, and Tie2Cre;RosatdTom lineage traced cells of controls and mutants were isolated by fluorescence activated cell sorting (FACS), after exclusion of blood cells (Ter119+, CD41+ and/or CD45+). FACS sorted Tie2Cre lineage from E12.5 hearts: Tie2Cre;Tbx20 +/loxP Control hearts versus Tie2Cre;Tbx20 loxP/- mutant hearts
Project description:Zebrafish heart regeneration is a complex process consisting of tempo-spatial coordination of cardiomyocyte (CM) and endothelial cell (EC) regeneration, fibrosis and inflammation. While myocardial, endocardial, and epicardial signaling have been reported to modulate this process, little is known about how leukocyte especially platelet signaling is involved in this regenerative process. Here we report that cloche/npas4l (neuronal PAS domain protein 4 like) is a pro-regenerative platelet factor for adult zebrafish heart regeneration. We found that injury triggered npas4l expression as early as 1 h post ventricular amputation, and haploinsufficiency of npas4l disrupted CM and EC proliferation and heart regeneration in clofv087b/+ and clom39/+ mutants after ventricular resection or nitroreductase (NTR)-mediated CM ablation. By constructing a single-cell transcriptomic atlas, we discovered that npas4l was dynamically expressed in platelets in response to heart injury with robust platelet-CM or -EC interactions via ligand-receptor activity analysis. Decreasing platelets in NTR-mediated depletion or mpl mutants impaired CM and EC proliferation, and over-expression of npas4l in platelets sufficiently made uninjured and injured CM reentry into the cell-cycle and rescued CM and EC proliferation in clofv087b/+ mutants. Furthermore, Npas4l positively regulated Bmp6 expression in platelets and either BMP6 inhibitors or siRNAs decreased CM proliferation and heart regeneration. This work demonstrates, for the first time, that injury-induced platelets are essential for zebrafish heart regeneration and Npas4l is a core platelet transcription factor for fine-tuning heart regeneration partially via Bmp6 signaling.
Project description:Zebrafish heart regeneration is a complex process consisting of tempo-spatial coordination of cardiomyocyte (CM) and endothelial cell (EC) regeneration, fibrosis and inflammation. While myocardial, endocardial, and epicardial signaling have been reported to modulate this process, little is known about how leukocyte especially platelet signaling is involved in this regenerative process. Here we report that cloche/npas4l (neuronal PAS domain protein 4 like) is a pro-regenerative platelet factor for adult zebrafish heart regeneration. We found that injury triggered npas4l expression as early as 1 h post ventricular amputation, and haploinsufficiency of npas4l disrupted CM and EC proliferation and heart regeneration in clofv087b/+ and clom39/+ mutants after ventricular resection or nitroreductase (NTR)-mediated CM ablation. By constructing a single-cell transcriptomic atlas, we discovered that npas4l was dynamically expressed in platelets in response to heart injury with robust platelet-CM or -EC interactions via ligand-receptor activity analysis. Decreasing platelets in NTR-mediated depletion or mpl mutants impaired CM and EC proliferation, and over-expression of npas4l in platelets sufficiently made uninjured and injured CM reentry into the cell-cycle and rescued CM and EC proliferation in clofv087b/+ mutants. Furthermore, Npas4l positively regulated Bmp6 expression in platelets and either BMP6 inhibitors or siRNAs decreased CM proliferation and heart regeneration. This work demonstrates, for the first time, that injury-induced platelets are essential for zebrafish heart regeneration and Npas4l is a core platelet transcription factor for fine-tuning heart regeneration partially via Bmp6 signaling.
Project description:Zebrafish heart regeneration is a complex process consisting of tempo-spatial coordination of cardiomyocyte (CM) and endothelial cell (EC) regeneration, fibrosis and inflammation. While myocardial, endocardial, and epicardial signaling have been reported to modulate this process, little is known about how leukocyte especially platelet signaling is involved in this regenerative process. Here we report that cloche/npas4l (neuronal PAS domain protein 4 like) is a pro-regenerative platelet factor for adult zebrafish heart regeneration. We found that injury triggered npas4l expression as early as 1 h post ventricular amputation, and haploinsufficiency of npas4l disrupted CM and EC proliferation and heart regeneration in clofv087b/+ and clom39/+ mutants after ventricular resection or nitroreductase (NTR)-mediated CM ablation. By constructing a single-cell transcriptomic atlas, we discovered that npas4l was dynamically expressed in platelets in response to heart injury with robust platelet-CM or -EC interactions via ligand-receptor activity analysis. Decreasing platelets in NTR-mediated depletion or mpl mutants impaired CM and EC proliferation, and over-expression of npas4l in platelets sufficiently made uninjured and injured CM reentry into the cell-cycle and rescued CM and EC proliferation in clofv087b/+ mutants. Furthermore, Npas4l positively regulated Bmp6 expression in platelets and either BMP6 inhibitors or siRNAs decreased CM proliferation and heart regeneration. This work demonstrates, for the first time, that injury-induced platelets are essential for zebrafish heart regeneration and Npas4l is a core platelet transcription factor for fine-tuning heart regeneration partially via Bmp6 signaling.
Project description:The development of a vascular network is essential to nourish tissues and sustain organ function throughout life. Endothelial cells (ECs) are the building blocks of blood vessels, yet our understanding of EC specification in vertebrates remains incomplete. cloche/npas4l mutants have broadly been used as an avascular model in zebrafish, but little is known about the molecular mechanism of action of Npas4l. Here, to identify the direct and indirect target genes of this transcription factor, we combined complementary genome-wide approaches, including transcriptome analyses and chromatin immunoprecipitation (ChIP). The cross-analysis of these datasets indicate that Npas4l functions as a master regulator by directly inducing a wave of transcription factor genes crucial for hematoendothelial specification in vertebrates, including etv2, tal1, and lmo2. We identified additional target genes acting downstream of npas4l and investigated the function of a subset of them using CRISPR/Cas9 technology. Phenotypic characterization of tspan18b mutants reveals a novel role for tspan18b in developmental angiogenesis, confirming the reliability of the datasets generated. Collectively, these data represent a useful resource for future studies aimed to investigate novel genes with a potential role in vascular development and EC fate determination in vertebrates.
Project description:The development of a vascular network is essential to nourish tissues and sustain organ function throughout life. Endothelial cells (ECs) are the building blocks of blood vessels, yet our understanding of EC specification in vertebrates remains incomplete. cloche/npas4l mutants have broadly been used as an avascular model in zebrafish, but little is known about the molecular mechanism of action of Npas4l. Here, to identify the direct and indirect target genes of this transcription factor, we combined complementary genome-wide approaches, including transcriptome analyses and chromatin immunoprecipitation (ChIP). The cross-analysis of these datasets indicate that Npas4l functions as a master regulator by directly inducing a wave of transcription factor genes crucial for hematoendothelial specification in vertebrates, including etv2, tal1, and lmo2. We identified additional target genes acting downstream of npas4l and investigated the function of a subset of them using CRISPR/Cas9 technology. Phenotypic characterization of tspan18b mutants reveals a novel role for tspan18b in developmental angiogenesis, confirming the reliability of the datasets generated. Collectively, these data represent a useful resource for future studies aimed to investigate novel genes with a potential role in vascular development and EC fate determination in vertebrates.