(A–B) Activation of the p53 biosensor (green) in the germarium of piRNA mutants, (A) cutoff[QQ}/[WM] and (B) aubergine[HN]/[QC]. (C) Activation of the p53 biosensor in rad54, a meiotic DNA repair mutant. (D–F) Germaria were found to express p53R-GFPcyt in GSCs/CBs with a penetrance of 90% for cutoff mutants (D, p<0.0001), 80% for aubergine mutants (E, p=0.0018), and 33% for rad54 mutants (F, p=0.0039). Asterisks indicate significant differences between heterozygous controls and homozygous mutants. GSCs/CBs were identified by rounded fusomes detected with α-HTS (red in merge A, B, C and white in A’, B’, C’). Arrowheads indicate that p53R-GFP positive cells are also germ cells identified by Vasa staining (blue in A, B, C and white split channel in A’’, B’’, C’’). Note that this particular α-Vasa antibody cross-reacts against the muscle sheath that surrounds each ovariole. If the sheath is not fully dissected and removed, then background staining is evident, as seen in Figure 2B′′. Control genotypes were cuff[WM]/CyO, aub[HN]/CyO, rad54[AA]/CyO. Note that aub and rad54 mutants occasionally showed p53 activation beyond region 2 of the germarium (arrow in C), quantified in Figure 3—figure supplement 1, Figure 3—source data 1. All scale bars represent 10 μm. In panels A, B, and C, the p53R-GFPcyt reporter was used.