Deregulated SRC activity causes border cells to engulf polar cells. (A) Schematic representation of the domains found in human SRC kinase and the important regulatory sites of tyrosine phosphorylation in the SH1 domain (Tyr419) and in the C-terminal tail (Tyr530). (B) Schematic representation of intramolecular interactions of human SRC in inactive and active conformations. (C–E) Single sections from confocal images of egg chambers at stages 9 and 10 expressing UAS-PLCδPHGFP to label membranes and UAS-lacZ as a negative control. Egg chambers were stained with FAS3 (magenta) and DAPI (blue). Yellow arrows point to the border cell cluster, and dashed white arrows indicate the migration path. NC: nurse cell nuclei. Scale bar, 50 µm. (F–L2) Single sections from confocal images of border cell clusters from egg chambers at stage 9 or 10 expressing UAS-PLCδPHGFP and the indicated UAS transgenes. Polar cells are identified by FAS3 (magenta) and DAPI labels DNA (blue). White asterisks in F and G indicate non-internalized polar cells and yellow asterisks in I, J, K1, K2, L1, and L2 indicate internalized polar cells. (H) White arrows in H point to polar cell nuclei being pinched by border cells. (K1 and K2) Images show two different focal planes of the same cluster, as well as L1 and L2 images. Scale bar: 5 µm. (F’–L2’) Segmentation and 3D reconstructions of the images in F–L2. (M) Quantifications of polar cell internalization from egg chambers at stage 10 of the indicated genotypes. Error bars: mean ± SEM (n = 3 independent experiments). The total number of clusters analyzed (n) is indicated at the top of each bar.