Fig. 1. DNA replication in gnu embryos. (A-D) Fluorescently immunostained eggs and embryos from gnu homozygous mothers. A nuclear lamina surrounded each of the giant nuclei in one embryo (A) but in this same embryo, only one nucleus stained for Drosophila PCNA (B). In another embryo, (C) DNA staining revealed three giant nuclei and, (D) following 5 minutes incubation, only one had incorporated BrdU. This indicated that not all of the nuclei are in S phase. (E,F) A 5 µm confocal section of an unfertilised egg (E) and embryo (F) stained for ß-tubulin in green and DNA in red. Microtubule asters were initiated in the fertilised embryo from duplicating centrosomes, but were not present in the unfertilised egg. Scale bars: 50 µm (A-D), 25 µm (E,F).