Understanding the role of PaK1 in zebrafish development

Proper neural crest development and migration is critical during embryonic development, but the molecular mechanisms regulating this process remain incompletely understood. As zebrafish maintain transparency throughout development, they can be utilized to aid in developmental studies. This thesis explores the role of p21-actived kinase-1 (Pak1) in zebrafish development. Morpholino technology was utilized to knock down Pak1 in the zebrafish embryo resulting in neural crest defects, characterized by a linear heart tube and outflow tract blockage, impaired melanophore development and migration, and aberrant cartilage structure, with associated defects in neural crest cell migration. Through the injection of mRNA, these defects could be rescued by human Pak1, but not a kinase dead form suggestive that the function of Pak1 is conserved between humans and fish and that Pak1 is operating as a kinase and not as a scaffolding protein, a role which has been previously implicated. Further rescue experiments show that the protein kinase Erk, which plays a central role in a number of key developmental processes in vertebrates, was regulated by Pak1 in the developing neural crest. Additional rescue experiments show that activated Erk signals by phosphorylating the transcription factor Gata6 on a conserved serine residue to promote neural crest migration and proper formation of craniofacial structures, pigment cells, and the outflow tract of the heart. These data suggest a previously unrecognized and essential role for Pak1 as an Erk activator, and Gata6 as an Erk target, during neural crest development.