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Fig. S1. KI67 expression during embryonic male germ cell development. Confocal microscopy images of Oct4::GFP transgenic, E13.5 testes immunostained for KI67 and E15.5 testes immunostained for KI67 and E-cadherin: (A) E13.5 FVB, (B) E13.5 M19, (C) E15.5 FVB and (B) E15.5 M19. KI67-positive, E-cadherin-negative E15.5 germ cells are indicated (arrow). Scale bars: 75 µm.
Fig. S2. CCND1 expression is downregulated with the initiation of meiosis in female germ cells. Confocal microscopy images of Oct4::GFP transgenic E15.5 female germ cells immunostained for CCND1 and γH2A.X. (A) CCND1 and γH2A.X immunostaining are shown for the E15.5 Oct4::GFP transgenic female gonad shown in Fig. 1. Dotted lines indicate the boundary at which germ cells transition from mostly γH2A.X-positive to mostly CCND1-positive. The anterior (A) to posterior (P) axis is indicated. Scale bar: 150 µm. (B) Magnified view of CCND1 and γH2A.X staining in E15.5 female germ cells. CCND1 and γH2A.X are not expressed in the same cells. Scale bar: 75 µm.
Fig. S3. Co-expression of CCND1, NANOG and KI67 in EC cell foci at E16.5. (A) Single color panels of CCND1, NANOG, or KI67 and E-cadherin staining in serial sections of an Oct4::GFP transgenic, E16.5 M19 testis (same testis as shown in Fig. 6B). E-cadherin-positive, low GFP-expressing EC cell foci are indicated (arrows). Scale bar: 150 µm. (B) Confocal microscopy images of serial sections of an E16.5 FVB testis stained for CCND1, NANOG or KI67. Oct4::GFP transgenic germ cells are negative for both CCND1 and NANOG. Scale bar: 75 µm.
Fig. S4. SYCP3 and SYCP1 localization in germ cells. Chromosome spreads from E14.5 and E16.5 gonads were stained for DAPI and SYCP3 or SYCP1, and imaged by confocal microscopy. (A) Pre-leptotene, nucleolar localization of SYCP3 in E14.5 M19 male germ cells. Scale bar: 100 µm. (B) Pachytene distribution of SYCP1 on synapsed chromosomes in an E16.5 female germ cell. Teratoma-resistant and susceptible male germ cells were negative for SYCP1 staining (not shown). Scale bar: 10 µm.