Chemical inhibition of Top2a disrupts pre-MZT development of zebrafish embryos. A) Schematic of the experimental procedure. 1-2 cell stage embryos were treated with Top2a inhibitors for 1.5 hours and their developmental progression was analysed. B-C) Graphs representing the percentage of embryos at a range of developmental stages following treatment with ICRF-193 (B) or etoposide (C). Top2a inhibition changes the staging distribution of embryos which peak at 16-32 cell stage in vehicle controls (DMSO) to peaking at the 8-16 cell stage in drug treated populations. The "unclassified" category includes embryos that do not fit into the standard developmental morphologies, ones in which all cells do not have typical optical transparency, and ones that are malformed. D) Table grouping the percentage of embryos at ≤ 16 cell stage or ≥ 32 cell stage for each drug treatment. Top2a inhibition increases the number of embryos ≤ 16 cell stage by up to 26%, and decreases the number of embryos ≥ 32 cell stage by up to 35%. Asterisks represent statistically significant differences (p < 0.005) to DMSO controls.