Open Access Research article

Maternal topoisomerase II alpha, not topoisomerase II beta, enables embryonic development of zebrafish top2a-/- mutants

Beata Sapetto-Rebow1, Sarah C McLoughlin15, Lynne C O'Shea1, Olivia O'Leary1, Jason R Willer2, Yolanda Alvarez1, Ross Collery16, Jacintha O'Sullivan3, Freek Van Eeden4, Carmel Hensey1 and Breandán N Kennedy1*

Author Affiliations

1 UCD School of Biomolecular and Biomedical Science, UCD Conway Institute, University College Dublin, Dublin, Ireland

2 Department of Biochemistry and Molecular Biology, University of Louisville, Louisville, KY, USA

3 St. James's Hospital, Trinity College Dublin, Dublin, Ireland

4 Department of Biomedical Science, University of Sheffield, Sheffield, UK

5 Institute for Translational Medicine and Therapeutics, School of Medicine, University of Pennsylvania, Philadelphia, PA, USA

6 Department of Cell Biology, Neurobiology & Anatomy, Medical College of Wisconsin, Milwaukee, WI, USA

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BMC Developmental Biology 2011, 11:71  doi:10.1186/1471-213X-11-71

Published: 23 November 2011



Genetic alterations in human topoisomerase II alpha (TOP2A) are linked to cancer susceptibility. TOP2A decatenates chromosomes and thus is necessary for multiple aspects of cell division including DNA replication, chromosome condensation and segregation. Topoisomerase II alpha is also required for embryonic development in mammals, as mouse Top2a knockouts result in embryonic lethality as early as the 4-8 cell stage. The purpose of this study was to determine whether the extended developmental capability of zebrafish top2a mutants arises from maternal expression of top2a or compensation from its top2b paralogue.


Here, we describe bloody minded (blm), a novel mutant of zebrafish top2a. In contrast to mouse Top2a nulls, zebrafish top2a mutants survive to larval stages (4-5 day post fertilization). Developmental analyses demonstrate abundant expression of maternal top2a but not top2b. Inhibition or poisoning of maternal topoisomerase II delays embryonic development by extending the cell cycle M-phase. Zygotic top2a and top2b are co-expressed in the zebrafish CNS, but endogenous or ectopic top2b RNA appear unable to prevent the blm phenotype.


We conclude that maternal top2a enables zebrafish development before the mid-zygotic transition (MZT) and that zebrafish top2a and top2b are not functionally redundant during development after activation of the zygotic genome.