The regions of spermatogenesis were apparent in mated males following 3 weeks of mating activity in control testis tubules (A and B) and the evidence of both mitotic division in spermatogonia in region II (B, arrowhead) and the band of meiotic divisions in region III was clear from anti-phosphohistone H3 staining. In Dnmt1 knockdown males at low magnification (C), the anterior tip, region II, of the testis tubule looked relatively normal. However, region III containing both the primary and secondary spermatocytes was disorganized. Spermatocyst structure was broken down, and the nuclei of the primary and secondary spermatocytes had lost their characteristic structure (Ewen-Campen et al., 2013). Finally, there were fewer mature spermatids in the posterior end of the testis tubule. At higher magnification (D), it was apparent that nuclear structure in the anterior tip was also affected by the knockdown, both in the spermatogonia and spermatocytes. Spermatogonia nuclei in the Dnmt1 knockdown testis tubules (D) were more condensed than in the control testis tubules (B), although they still seemed to be organized into spermatocysts. Spermatocyte nuclei, however, were fewer in number than in controls, did not have their characteristic shape (Ewen-Campen et al., 2013; Economopoulos and Gordon, 1971), and were not organized in spermatocytes. A and C:10× magnification, B and D: 20× magnification.