Zombie gene function is necessary for mitosis after gastrulation: Is zombie really zebrafish CDC20?

Abstract

Cell cycle controllers are proteins that govern cycle checkpoints, in turn, ensuring successful duplication of the genome. Understanding the genes that encode for these controllers and the interactions of their protein products could lead to a deeper understanding of what causes cells to exit the cell cycle through differentiation. A deeper understanding of these controllers would aid in developing therapies for those diseases, such as cancer, that bypass these checkpoints. The zombie mutant in zebrafish has been identified as a possible cell cycle mutant. Previous studies found it bears a phenotypic resemblance to the Drosophila mutant fizzy. Fizzy encodes for cell division cycle 20 (CDC20), a protein activator of the anaphase promoting complex/cyclosome (APC/C). Activation of APC/C through CDC20 association allows cells to transition from metaphase into anaphase. The goal of the present study was to more precisely characterize the zombie mutant, which provided two cytological assays, and to test the idea that zombie is CDC20. Antibody staining for phosphorylated histone H3, a marker of condensed DNA, showed an increase in mitotic cells in zombie mutants compared to wild-type siblings as early as the 3-somite stage. Of the cells in mitosis, zombie mutants also showed a greater amount of cells in metaphase supporting the assertion that zombie is CDC20. However, ectopic expression of Xenopus CDC20 in zombie embryos showed no phenotypic or cytological rescue of the mutant phenotype. In addition, knock-down of CDC20 in wild-type showed no phenocopy of the zombie mutant phenotype. Despite the increased characterization, these combined data indicate that further experimentation is needed to assert that zombie is a mutation of CDC20.