Unmasking Activation of the Zygotic Genome Using Chromosomal Deletions in the Drosophila Embryo
Figure 2
Ablation of the X, 2-Entire, 3-Entire Chromosomes and Identification of Mutant Embryos
(A, C, E, and H) Live embryos were imaged using an up-right microscope. Arrowhead indicates the phenotypes associated with each chromosomal ablation. (A) shows a WT embryo. In (C), an X− embryo shows the irregular cellularization front (nullo phenotype) due to the failure to form furrow canals around some nuclei. (E) The 2− embryo developed the characteristic halo phenotype: a dark cytoplasmic halo below the nuclei. (H) The 3− embryo developed the bottleneck phenotype. Nuclei failed to be incorporated in the cellularization front because of the early and uncontrolled contractility of the actin-myosin network.
(B, D, F, G, I, and J) Immunostaining using anti-Armadillo (B and D) and anti Myosin-2 antibodies (F, G, I, and J). (B) and (D) show the apical surface, top view, of WT and X− embryos respectively. Arrowhead indicates the irregular conformation of the apical membrane in the X− embryo. (F and G) Optical cross section of WT (F) and 2− (G) embryos stained with anti-myosin-2 antibodies. Note the lack of cell membranes in 2− embryos and failure to localize myosin-2 to the basal side of the cellularization front. (I and J) Top view of WT (I) and 3− (J) embryos stained with anti-myosyn-2 antibodies showing the typical bottleneck phenotype, arrowhead in (J).
(K) Table summarizing the results of each chromosomal manipulation. The chromosomal location of down-regulated genes (3-fold, p < 0.001) is plotted next to the corresponding embryo. Data were obtained using four biological replicates (ablation of chromosome X and 2) and two biological replicates (ablation of Chromosome 3 entire).