Characterization of zebrafish zipper-interacting protein kinase

Zipper-Interacting Protein Kinase (ZIPK) is a known modulator of actin-myosin contractility in vertebrate species. Interestingly, rodent and mouse ZIPK has undergone a divergence in regulation in comparison to other vertebrate orthologs including human. Whereas the human ortholog of ZIPK requires phosphorylation of residues TT299/300 for nuclear exit, rodents and mouse require interaction with another protein termed PAR-4. In this project we completed several experiments to examine zebrafish ZIPK in development and its effect on acto-myosin contractility. It was found that zebrafish ZIPK was expressed ubiquitously in maternal stages. In zygotic stages, ZIPK expression dropped dramatically and localized to the anterior portions of the embryo. Zebrafish and human ZIPK, but not rodent ZIPK were able to increase stress fiber formation and myosin light chain-2 (MLC-2) phosphorylation in vitro. Human and zebrafish ZIPK underwent nucleocytoplasmic shuttling without PAR-4 interaction, unlike rodent ZIPK, which required PAR-4 for nuclear exit. Unlike human ZIPK, zebrafish ZIPK TT299/300AA mutants were able to undergo shuttling. Similar to human ZIPK, catalytic mutations to zebrafish ZIPK abolished or dramatically reduced activity. Through these experiments we were able to show human and zebrafish ZIPK homologs function and are regulated similarly, while the rodent ZIPK was much more unique. Although the exhibited phenotypes were similar between human and zebrafish ZIPK orthologs, the mechanism of regulation is not completely conserved