Histone methyltransferase PRDM9 is not essential for meiosis in male mice

Similar meiotic arrest in B6 and PWD females lacking functional Prdm9. (A) Reduced adult ovary weight in both B6^tm/tm and PWD^tm/tm females indicative of arrested meiosis. There is no significant difference between B6^tm/tm and PWD^tm/tm. Black dots with bars symbolize mean ± SD; color dots depict individuals. Tukey's box-and-whisker plots show median values and quartiles. H/E-stained sections of paraffin-embedded ovaries of adult (B) and 2 d after birth (dpp) (C) mice. Arrows point to oocytes present in the controls but mostly absent in both PWD^tm/tm and B6^tm/tm. (D) Oocytes from newborn ovaries immunostained with anti-MSY2 (YBX2) antibody Abcam (ab33164) and DAPI. The number of oocytes was comparable in all tested females at birth (D), but decreased in both types of Prdm9-deficient mice compared to littermate controls 2 d after birth (C), suggesting pachytene arrest attributable to oocyte attrition. (E) Reduced homologous chromosome synapsis in PWD^tm/tm oocytes (∼18 d post coitum). Colors distinguish oocytes derived from individual embryos (2 PWD^wt/wt, 4 PWD^wt/tm, and 6 PWD^tm/tm). Black dots represent mean values, and bars represent SDs. (F) Representative spread nuclei from the PWD^tm/tm and PWD^wt/tm oocytes in E. Nuclei were immunostained for the synaptonemal complex lateral element (SYCP3), central element (SYCP1; yellow color indicates synapsis), and gamma H2AFX (a chromatin marker of DNA damage). (G) Decreased chromosomal synapsis in both PWD and B6 newborn oocytes lacking functional PRDM9. (H) Representative nuclei from the PWD^tm/tm and PWD^wt/tm oocytes in G immunostained for the synaptonemal complex central element (SYCP1; green indicates synapsis), recombination nodules (MLH1), and centromeres (CENT). See Supplemental Fig. S4 for nuclei from B6^tm/tm and B6^wt/wt.