In leptotene and once formed are recognised by HR repair machinery such that by pachytene most DSBs are repaired [20]. To investigate whether the Ggn+/2 spermatocytes have impaired DSB repair, spermatocyte chromatin spreads coupled with immunostaining were used. Spermatocyte chromatin spreads were prepared from Ggn+/+ and Ggn+/2 mice and double labelled with antibodies to the synaptonemal complex, SYCP3, as a marker of paired homologous chromosomes, and RAD51, as a marker of unrepaired DSBs. If GGN was involved in DSB repair during meiosis, then one possibility was that once the breaks were induced they would not be repaired. If this were the case we would observe more unrepaired breaks during pachynema. We analysed and quantified RAD51 foci on the autosomes and XY SQ 34676 chromosomes of pachytene cells from the Ggn+/+ the Ggn+/2 mice (Figure 3C) (n = 7 mice per group, 50 pachytene cells counted per mouse, 350 cells per group). RAD51 foci per pachytene cell on the XY chromosomes were not significantly different between the Ggn+/2 (6.7860.44) and Ggn+/+ (5.7460.45) males (P = 0.06). However, we observed a statistically significant increase in autosomal RAD51 foci in the Ggn+/2 males compared to that of Ggn+/+ littermates (P = 0.04, 15.7162.08 for the Ggn+/+ males and 11.4061.12 for the Ggn+/+ males) (Figure 3D). Persistence 16402044 of RAD51 foci in Ggn+/2 pachytene spermatocytes indicated that meiotic DSB repair was impaired. Collectively these results suggest a role for GGN in DSB repair during male meiosis. Many mouse models of Fanc protein deficiency exhibit fertility defects including those for Fancl [21], Fanca [22,23], Fancc [24], Fancg [25,26] and Fancd2 [27]. Moreover, Fanca and Fancd2 knockout spermatocytes showed elevated frequency of mispaired meiotic chromosomes [23,27]. These observations highlight the critical role for the FA Erastin site pathway in the maintenance of genome integrity in both somatic and germ cells. Herein we demonstrated that GGN1 as an endogenous binding partner of FANCL, FANCD2 and BRCC36 in the testis, and provide data to support a role for GGN in DSB repair during male meiosis. In order to definitely make such claims, however, it will be necessary to produce a testis-specific Ggn knockout model. Unfortunately this was not possible using the targeting strategy we have employed.Table 1. Targeted deletion of the mouse Ggn gene resulted in pre-implantation embryonic lethality.Age of progenyLitter size Number analysed (Mean6S.D.)Genotype Number of Ggn+/+ Number of Ggn+/2 123 (70 ) 35 (73 ) 34 (71 ) 34 (76 ) 27 (55 ) Number of Ggn2/2 0 0 0 1* (2 ) 10 (20 )3 week E11.5 13.5 E7.5 8.5 E2.5 3.5 2-cell IVF embryos2/175 48 48 457.962.1 9.562.0 9.761.7 not analysed not analysed52 (30 ) 13 (27 ) 14 (29 ) 15900046 10 (22 ) 12 (25 )embryo identified at morula stage of development. *indicates a Ggn doi:10.1371/journal.pone.0056955.tGGN Regulates Embryogenesis and Meiotic DSB RepairFigure 2. Ggn2/2 embryos die prior to implantation. (A) Targeting strategy used for disruption of the mouse Ggn gene and for screening of the targeted ES clones (B) Southern blotting using 59 and 39 external probes. (C) Genotyping of pre-implantation embryos collected from Ggn+/2 timed mating. *indicates a Ggn2/2 embryo identified at morula stage of development. (D) Ggn is expressed in mouse oocytes and pre-implantation embryos. (E) Ggn is expressed at high levels within the adult testis and at a low level in the ovary and somatic tissues. All adult tissues were obtained from 10.In leptotene and once formed are recognised by HR repair machinery such that by pachytene most DSBs are repaired [20]. To investigate whether the Ggn+/2 spermatocytes have impaired DSB repair, spermatocyte chromatin spreads coupled with immunostaining were used. Spermatocyte chromatin spreads were prepared from Ggn+/+ and Ggn+/2 mice and double labelled with antibodies to the synaptonemal complex, SYCP3, as a marker of paired homologous chromosomes, and RAD51, as a marker of unrepaired DSBs. If GGN was involved in DSB repair during meiosis, then one possibility was that once the breaks were induced they would not be repaired. If this were the case we would observe more unrepaired breaks during pachynema. We analysed and quantified RAD51 foci on the autosomes and XY chromosomes of pachytene cells from the Ggn+/+ the Ggn+/2 mice (Figure 3C) (n = 7 mice per group, 50 pachytene cells counted per mouse, 350 cells per group). RAD51 foci per pachytene cell on the XY chromosomes were not significantly different between the Ggn+/2 (6.7860.44) and Ggn+/+ (5.7460.45) males (P = 0.06). However, we observed a statistically significant increase in autosomal RAD51 foci in the Ggn+/2 males compared to that of Ggn+/+ littermates (P = 0.04, 15.7162.08 for the Ggn+/+ males and 11.4061.12 for the Ggn+/+ males) (Figure 3D). Persistence 16402044 of RAD51 foci in Ggn+/2 pachytene spermatocytes indicated that meiotic DSB repair was impaired. Collectively these results suggest a role for GGN in DSB repair during male meiosis. Many mouse models of Fanc protein deficiency exhibit fertility defects including those for Fancl [21], Fanca [22,23], Fancc [24], Fancg [25,26] and Fancd2 [27]. Moreover, Fanca and Fancd2 knockout spermatocytes showed elevated frequency of mispaired meiotic chromosomes [23,27]. These observations highlight the critical role for the FA pathway in the maintenance of genome integrity in both somatic and germ cells. Herein we demonstrated that GGN1 as an endogenous binding partner of FANCL, FANCD2 and BRCC36 in the testis, and provide data to support a role for GGN in DSB repair during male meiosis. In order to definitely make such claims, however, it will be necessary to produce a testis-specific Ggn knockout model. Unfortunately this was not possible using the targeting strategy we have employed.Table 1. Targeted deletion of the mouse Ggn gene resulted in pre-implantation embryonic lethality.Age of progenyLitter size Number analysed (Mean6S.D.)Genotype Number of Ggn+/+ Number of Ggn+/2 123 (70 ) 35 (73 ) 34 (71 ) 34 (76 ) 27 (55 ) Number of Ggn2/2 0 0 0 1* (2 ) 10 (20 )3 week E11.5 13.5 E7.5 8.5 E2.5 3.5 2-cell IVF embryos2/175 48 48 457.962.1 9.562.0 9.761.7 not analysed not analysed52 (30 ) 13 (27 ) 14 (29 ) 15900046 10 (22 ) 12 (25 )embryo identified at morula stage of development. *indicates a Ggn doi:10.1371/journal.pone.0056955.tGGN Regulates Embryogenesis and Meiotic DSB RepairFigure 2. Ggn2/2 embryos die prior to implantation. (A) Targeting strategy used for disruption of the mouse Ggn gene and for screening of the targeted ES clones (B) Southern blotting using 59 and 39 external probes. (C) Genotyping of pre-implantation embryos collected from Ggn+/2 timed mating. *indicates a Ggn2/2 embryo identified at morula stage of development. (D) Ggn is expressed in mouse oocytes and pre-implantation embryos. (E) Ggn is expressed at high levels within the adult testis and at a low level in the ovary and somatic tissues. All adult tissues were obtained from 10.
