Normal body situs requires precise spatiotemporal expression of the Nodal-Lefty-Pitx2 cascade in the lateral plate mesoderm. The ultimate output of this patterning is establishment of the left-right axis, which provides vital cues for correct organ formation and function. Mutations, deletions and duplications in PITX2 and FOXC1 lead to the rare genetic disease Axenfeld-Rieger syndrome (ARS). While situs defects are not a recognised feature of ARS, partial penetrance of cardiac septal defects and valve incompetence is observed; both of these congenital heart defects (CHDs) also occur following disruption of left-right patterning. Here we investigated whether foxc1 genes have a critical role in specifying organ situs. We demonstrate that CRISPR/Cas9 generated mutants for the zebrafish paralogs foxc1a and foxc1brecapitulate ARS phenotypes including craniofacial dysmorphism, hydrocephalus and intracranial haemorrhage. Furthermore, foxc1a-/-; foxc1b-/- mutant animals display cardiac and gut situs defects. Modelling FOXC1 duplication by transient mRNA overexpression revealed that increased foxc1 dosage also results in organ situs defects. Analysis of known left-right patterning genes revealed a loss in expression of the NODAL antagonist lefty2 in the lateral plate mesoderm. Consistently, LEFTY2 mutations are known to cause human cardiac situs defects. Our data reveal a novel role for the forkhead-box transcription factor foxc1 in patterning of the left-right axis, and provide a plausible mechanism for the incidence of congenital heart defects in Axenfeld-Rieger syndrome patients.

中文翻译：

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Axenfeld-Rieger综合征基因FOXC1有助于左右模式

正常的体位需要外侧板中皮中的Nodal-Lefty-Pitx2级联的精确时空表达。这种图案的最终输出是左右轴的建立，这为正确的器官形成和功能提供了重要线索。PITX2和FOXC1中的突变，缺失和重复会导致罕见的遗传疾病Axenfeld-Rieger综合征（ARS）。虽然部位缺陷不是ARS的公认特征，但可以观察到心脏间隔缺损的部分渗透和瓣膜功能不全。这两种先天性心脏缺陷（CHD）也会在左右图案中断后发生。在这里，我们调查了foxc1基因是否在指定器官部位中起关键作用。我们证明了CRISPR / Cas9产生的斑马鱼旁系同源物foxc1a和foxc1brecapitulate的突变体ARS表型包括颅面畸形，脑积水和颅内出血。此外，foxc1a-/-; foxc1b-/-突变动物表现出心脏和肠道部位缺陷。通过瞬时mRNA过表达对FOXC1复制进行建模显示，增加的foxc1剂量也会导致器官部位缺陷。对已知的左右模式基因的分析显示，NODAL拮抗剂lefty2在外侧板中胚层中表达的损失。一致地，已知LEFTY2突变会引起人心脏部位缺陷。我们的数据揭示了叉头盒转录因子foxc1在左右轴模式中的新作用，