Fig. 4. Secondary spermatogonia can undergo an extra round of mitosis in myt1 mutants. (A,B) Testes stained with anti-BamC (green) and anti-PH3 (red) antibodies. In the controls, cysts of dividing secondary spermatogonia do not contain more than eight cells (A, white arrows), whereas the myt1 mutant also contains a 16-cell cyst (B, white arrow), indicating an extra cell division. There were also many scattered PH3-positive cells not co-stained with BamC but intermingled with BamC-positive cells, in the myt1 mutants. These were probably ectopically dividing somatic cells (see Fig. 5, for explanation). (C-G) Phase-contrast and (C'-G') fluorescence (Hoechst 33258) images of cysts of: (C,C') control 16-cell primary spermatocytes, (D,D') unusual 32-cell spermatocyte cysts seen in myt1 mutants, (E,E') control 64-cell spermatid cysts, and aberrant-looking 64-cell (F,F') and 128-cell (G,G') spermatid cysts from myt1 mutants. Scale bars: in A, 20 µm for A,B; in D', 50 µm for C,D'; in G', 50 µm for E-G'.