Aims Bicuspid Aortic Valve (BAV) is the most common congenital heart defect, affecting at least 2% of the population. The embryonic origins of BAV remain poorly understood, with few assays for validating patient variants, limiting the identification of causative genes for BAV. In both human and mouse, the left and right leaflets of the arterial valves arise from the outflow tract cushions, with interstitial cells originating from neural crest cells and the overlying endocardium through endothelial-to-mesenchymal transition (EndoMT). In contrast, an EndoMT-independent mechanism of direct differentiation of cardiac progenitors from the second heart field (SHF) is responsible for the formation of the anterior and posterior leaflets. Defects in either of these developmental mechanisms can result in BAV. Although zebrafish have been suggested as a model for human variant testing, their naturally bicuspid arterial valve has not been considered suitable for understanding human arterial valve development. Here, we have set out to investigate to what extent the processes involved in arterial valve development are conserved in zebrafish and ultimately, whether functional testing of BAV variants could be carried out. Methods and Results Using a combination of live imaging, immunohistochemistry and Cre-mediated lineage tracing, we show that the zebrafish arterial valve primordia develop directly from SHF progenitors with no contribution from EndoMT or neural crest, in keeping with the human and mouse anterior and posterior leaflets. Moreover, once formed, these primordia share common subsequent developmental events with all three aortic valve leaflets. Conclusions Our work highlights a conserved ancestral mechanism of arterial valve leaflet formation from the SHF and identifies that development of the arterial valve is distinct from that of the atrioventricular valve in zebrafish. Crucially, this confirms the utility of zebrafish for understanding the development of specific BAV subtypes and arterial valve dysplasia, offering potential for high-throughput variant testing.

中文翻译：

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斑马鱼动脉瓣发育是通过第二心野祖细胞的直接分化发生的


目的 二叶式主动脉瓣 （BAV） 是最常见的先天性心脏缺陷，影响至少 2% 的人口。BAV 的胚胎起源仍然知之甚少，很少有用于验证患者变异的检测方法，限制了 BAV 致病基因的鉴定。在人和小鼠中，动脉瓣膜的左右小叶起源于流出道垫，间质细胞起源于神经嵴细胞和上覆的心内膜，通过内皮-间充质转化 （EndoMT）。相比之下，心脏祖细胞与第二心野 （SHF） 直接分化的 EndoMT 非依赖性机制负责前叶和后叶的形成。这些发育机制中的任何一个缺陷都可能导致 BAV。尽管斑马鱼已被建议作为人类变异测试的模型，但它们的天然二叶动脉瓣被认为不适合理解人类动脉瓣的发育。在这里，我们着手研究斑马鱼动脉瓣发育所涉及的过程在多大程度上是保守的，并最终研究是否可以对 BAV 变体进行功能测试。方法和结果 结合实时成像、免疫组化和 Cre 介导的谱系追踪，我们表明斑马鱼动脉瓣原基直接从 SHF 祖细胞发育而来，没有来自 EndoMT 或神经嵴的贡献，与人和小鼠前后小叶一致。此外，一旦形成，这些原基与所有三个主动脉瓣小叶共享共同的后续发育事件。 结论 我们的工作强调了 SHF 形成动脉瓣叶的保守祖先机制，并确定动脉瓣的发育与斑马鱼的房室瓣不同。至关重要的是，这证实了斑马鱼在了解特定 BAV 亚型和动脉瓣发育不良的发展方面的效用，为高通量变异测试提供了潜力。