(A) PAS histology in P56 testis sections. Scale bar, 50 µm. On the right are stylized depictions of the 100X panels. SG, spermatogonium; SC, spermatocyte; ST, spermatid, Lum, lumen; Ser, Sertoli cell cytoplasm. (B) FACS analysis of germ cells in WT and mutant testes. Testes were dissociated and FACS was used to quantify the number of mito-Dendra2-positive germ cells. Dendra fluorescence (x-axis) is shown in arbitrary units (au). The histograms were normalized by plotting the same number of somatic (mito-Dendra2-negative) cells between S8::Control and S8::Dm samples. (C) Quantification of the results from (B). N = 5. (D) Immunolabeling of the major germ cell types in WT and mutant animals. Scale bar, 20 µm. (E) Doughnut graphs indicating germ cell types in seminiferous tubule cross sections. Each seminiferous tubule cross section was scored for its most advanced germ cell type. Note that in WT tubules, all seminiferous tubules contain spermatids. For p-values, see Figure 4—figure supplement 1. N = 4. (F) Quantification of germ cell types per tubule cross section. Mutant values are plotted relative to control, which is set to 100% and indicated by the gray bar. N = 4. (G) Immunolabeling of stem-like spermatogonia. PLZF marks all undifferentiated spermatogonia and GFRα1 marks stem-like spermatogonia. Note that all GFRα1 spermatogonia express PLZF, but not vice versa. Scale bar, 20 µm. (H) Immunolabeling of the proliferation marker Ki-67 in GFRα1-expressing spermatogonia in testis section. Scale bar, 20 µm. (I) Percent of GFRα1-expressing spermatogonia that are positive for the proliferation marker Ki67. N = 4. (J) Schematic of normal spermatogenesis (left) and the defect in P56 S8::Dm mice (right). SPZ, spermatozoon; ST, spermatid; MPI; Meiotic Prophase I; SC, spermatocyte; P/D, pachytene/diplotene; L/Z, leptotene/zygotene; SG, spermatogonium. Ac, acrosome, XY, sex body; PM, plasma membrane; Nuc, nucleus. N ≥ 4, unless otherwise indicated. Data are represented as mean ± SEM. ****p≤0.0001; ***p≤0.001. For statistical tests used, see the Materials and methods section.