Neuron Navigator 3 (NAV3) is Required for Heart Development

Background: As a tightly controlled biological process, cardiogenesis requires the specification and migration of a suite of cell types to form a particular three-dimensional configuration of the heart. Many genetic factors are involved in the formation and maturation of the heart, and any genetic mutations may result in severe cardiac failures. The neuron navigator (NAV) family consists of three vertebrate homologs (NAV1, NAV2, and NAV3) of the neural guidance molecule Uncoordinated-53 (UNC-53) in Caenorhabditis elegans. Although they are recognized as neural regulators, their expressions are also detected in many organs, including the heart, kidney, and liver. However, the functions of NAVs, regardless of neural guidance, remain largely unexplored. In this study, we aim to investigate the role of NAV3 in heart development. Results: The nav3 gene was found to be expressed in the cardiac region of zebrafish embryos from 24 to 48 hours post-fertilization (hpf) by means of in situ hybridization (ISH) assay. A CRISPR/Cas9-based genome editing method was utilized to delete the nav3 gene in zebrafish and loss-of-function of Nav3 resulted in a severe deficiency in its cardiac morphology and structure. The similar phenotypic defects of the knockout mutants could recur by nav3 morpholino injection and be rescued by nav3 mRNA injection. Dual-color fluorescence imaging of ventricle and atrium markers further confirmed the disruption of the heart development in nav3-deleted mutants. Although the heart rate was not affected by the deletion of nav3, the heartbeat intensity was decreased in the mutants. Conclusions: The nav3 gene can be expressed in a variety of tissues or organs although it is initially identified as a neural guiding factor. Gene knockout of nav3 in zebrafish leads to severe development malformation of the heart. Moreover, the defective heart development can be rescued by nav3 mRNA injection. All these findings indicate that Nav3 was required for cardiogenesis in the development of zebrafish embryos.