Rationale: The transcription factor NFATC1 has been implicated in cardiac valve formation in humans and mice, but we know little about the underlying mechanisms. To gain mechanistic understanding of cardiac valve formation at single cell resolution and insights into the role of NFATC1 in this process, we used the zebrafish model as it offers unique attributes for live imaging and facile genetics. Objective: To understand the role of Nfatc1 in cardiac valve formation. Methods and Results: Using the zebrafish atrioventricular (AV) valve, we focus on the valve interstitial cells (VICs) which confer biomechanical strength to the cardiac valve leaflets. We find that initially AV endocardial cells (ECs) migrate collectively into the cardiac jelly to form a bilayered structure; subsequently, the cells that led this migration invade the extracellular matrix (ECM) between the two EC monolayers, undergo endothelial-to-mesenchymal transition as marked by loss of intercellular adhesion, and differentiate into VICs. These cells proliferate and are joined by a few neural crest-derived cells. VIC expansion as well as a switch from a pro-migratory to an elastic ECM drive valve leaflet elongation. Functional analysis of Nfatc1 reveals its requirement during VIC development. Zebrafish nfatc1 mutants form significantly fewer VICs due to reduced proliferation and impaired recruitment of endocardial and neural crest cells during the early stages of VIC development. With high-speed microscopy and echocardiography, we show that reduced VIC formation correlates with valvular dysfunction and severe retrograde blood flow that persist into adulthood. Analysis of downstream effectors reveals that Nfatc1 promotes the expression of twist1b, a well-known regulator of epithelial-to-mesenchymal transition. Conclusions: Our study sheds light on the function of Nfatc1 in zebrafish cardiac valve development and reveals its role in VIC formation. It also further establishes the zebrafish as a powerful model to carry out longitudinal studies of valve formation and function.
Rationale: The transcription factor NFATC1 has been implicated in cardiac valve formation in humans and mice, but we know little about the underlying mechanisms. To gain mechanistic understanding of cardiac valve formation at single cell resolution and insights into the role of NFATC1 in this process, we used the zebrafish model as it offers unique attributes for live imaging and facile genetics. Objective: To understand the role of Nfatc1 in cardiac valve formation. Methods and Results: Using the zebrafish atrioventricular (AV) valve, we focus on the valve interstitial cells (VICs) which confer biomechanical strength to the cardiac valve leaflets. We find that initially AV endocardial cells (ECs) migrate collectively into the cardiac jelly to form a bilayered structure; subsequently, the cells that led this migration invade the extracellular matrix (ECM) between the two EC monolayers, undergo endothelial-to-mesenchymal transition as marked by loss of intercellular adhesion, and differentiate into VICs. These cells proliferate and are joined by a few neural crest-derived cells. VIC expansion as well as a switch from a pro-migratory to an elastic ECM drive valve leaflet elongation. Functional analysis of Nfatc1 reveals its requirement during VIC development. Zebrafishnfatc1 mutants form significantly fewer VICs due to reduced proliferation and impaired recruitment of endocardial and neural crest cells during the early stages of VIC development. With high-speed microscopy and echocardiography, we show that reduced VIC formation correlates with valvular dysfunction and severe retrograde blood flow that persist into adulthood. Analysis of downstream effectors reveals that Nfatc1 promotes the expression of twist1b, a well-known regulator of epithelial-to-mesenchymal transition. Conclusions: Our study sheds light on the function of Nfatc1 in zebrafish cardiac valve development and reveals its role in VIC formation. It also further establishes the zebrafish as a powerful model to carry out longitudinal studies of valve formation and function.
Entities:
Keywords:
Nfatc1; Transcriptional regulation; Valve interstitial celc; cardiac valve development