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.