Nusap1 is essential for neural crest cell migration in zebrafish

Microtubules play important roles in mitotic spindle assembly and chromosome segregation to maintain normal cell cycle progression. A number of microtubule-associated proteins have been identified in epithelial and neural cell cultures; however, their physiological significance is not well characterized due to the lack of appropriate in vivo animal models. Nucleolar spindle-associated protein (NuSAP) is a microtubule-binding protein and is reported to be involved in mitosis by cell culture studies. In this report, we identified the zebrafish homologue of human NuSAP and investigated its expression profile and functions. Using in situ hybridization, we demonstrated that transcripts of zebrafish nusap1 are specifically expressed in the retina, forebrain, hindbrain and neural crest. When the in vivo expression of nusap1 was knocked down through antisense oligonucleotide morpholino technology, the morphants of nusap1 showed impaired morphogenesis in the trunk and yolk extension, implying the involvement of Nusap1 in cell migration. Mechanistic studies revealed that nusap1 morphants have an altered expression pattern of neural crest markers crestin and sox9b, but normal expression of blood vessel and notochord markers gata1 and shh. In addition, nusap1 mRNA injection caused serious apoptosis in retina and hindbrain tissue, and these phenotypes can be rescued by co-injection of morpholino against nusap1. These observations not only suggest a role for Nusap1 in connecting apoptosis with cell migration, but also provide strong evidences that Nusap1 is potentially involved in morphogenesis in vertebrates.