Time-Mated Breeding to Acquire Rhesus Macaque Embryos at Carnegie Stage 23
(A) Strategy for rhesus macaque time-mated breeding using estrogen to monitor ovulation. Day 1 of embryo development (fertilization) was estimated to occur 72 hr after the estrogen peak.
(B) Estradiol measurements (pg/mL) in the serum of females (animal identification number is shown, n = 10 animals).
(C) Embryo crown rump length (mm) of Carnegie stage 23 embryos (n = 10 embryos).
(D) Embryo weight (g) of Carnegie stage 23 embryos (n = 10 embryos).
(E) A pair of embryonic testicles (T) isolated from a day 47 embryo, and associated mesonephros (m), indicated by the arrow.
(F) H&E stain of a testis at embryonic day 49 and associated mesonephros (m) with glomeruli. Scale bar, 200 μm.
(G) H&E stain of testis cords at embryonic day 49 (arrow points to cords). Scale bar, 50 μm.
(H) Immunofluorescence of embryonic testis at day 49 showing that cKIT-positive PGCs are depleted in 5mC (n = 1 embryonic testis, n = 2 technical duplicates). Scale bar, 10 μm.
(I) Immunofluorescence of embryonic testis at day 49 showing cKIT/OCT4 double-positive PGCs (n = 1 embryonic testis, n = 2 technical duplicate). Scale bar, 20 μm.

Rhesus PGCs Express PGC Transcription Factors and Are Localized in Testis Cords
(A) Immunofluorescence of embryonic testes at day 49 showing OCT4-positive PGCs within LAMININ-positive cords. Scale bar, 10 μm.
(B) Immunofluorescence for cKIT and VASA showing all cKIT-positive cells are VASA positive and localized in the cortex of the embryonic testes. Scale bar, 100 μm.
(C) Immunofluorescence for cKIT and VASA showing co-localization.
(D) Immunofluorescence for PRDM1 and OCT4 showing co-localization.
(E) Immunofluorescence for TFAP2C and OCT4 showing co-localization.
(F) Immunofluorescence for cKIT and SOX17 showing co-localization.
All experiments were performed on n = 1 embryonic testis at day 49 in technical duplicate. Scale bars, 20 μm unless otherwise stated.

Sorting Rhesus PGCs from Carnegie Stage 23 Gonads using cKIT
(A) FACS plot showing APC-conjugated cKIT antibody binding in rhesus fibroblasts (negative) and rhesus iPSCs (negative).
(B) Representative FACS plot showing APC-conjugated cKIT antibody binding in rhesus embryonic gonads at Carnegie stage 23.
(C) The percentage cKIT-positive rhesus PGCs in embryonic gonads. Each shape corresponds to cKIT-positive cells from the gonads of one embryo (n = 5 embryos total).
(D) Total number of cKIT-positive rhesus PGCs sorted from a pair of testes (n = 3 embryos) and a pair or ovaries (n = 1 embryo, pink arrow) at Carnegie stage 23.
(E) Single-cell analysis of 28 cKIT-APC sorted rhesus PGCs analyzed in technical triplicate for pluripotency and germline genes including OCT4, PRDM1, NANOS3, DAZL, and VASA. A standard curve was established using 1,000, 100, 10, and 0 cells. Yellow, high expression levels; black, background expression levels.
(F) Immunofluorescence for PRDM1 and VASA showing that the majority of VASA-positive cells are PRDM1-positive; however, a minor number of VASA-positive PRDM1-negative cells can be identified (arrow) (n = 1 day 49 embryonic testis, n = 2 technical duplicates). Scale bar, 20 μm.

Rhesus PGCs in Carnegie Stage 23 Are Equivalent to Human PGCs at 8–10 Weeks
(A) RNA-seq heatmap of cKIT-sorted PGCs from the gonads of n = 4 embryos. This includes the cKIT-positive population sorted from pairs of testes (n = 3 male embryos), and pairs of ovaries (n = 1 female embryo) with embryonic liver from the same embryos as a somatic cell control (n = 4 embryos). The age of the embryo is shown in days (d). The age shown in pink refers to the female samples. The ages shown in black are male samples. The numbers refer to the sample number. See also .
(B) RPKM (reads per kilobase of transcript per million mapped read) of selected genes enriched in rhesus PGCs relative to rhesus embryonic liver cells. Data are shown as average of n=4 embryos with mean and SD.
(C) RPKM of selected genes encoding receptors. Data are shown as average of n=4 embryos with mean and SD.
(D) RPKM values of selected genes enriched in PGCs that are also involved in chromatin regulation. Data are shown as average of n=4 embryos with mean and SD.
(E) Immunofluorescence of histone H3 lysine 9 dimethylation (H3K9me2) in VASA-positive PGCs (circled in white). Most PGCs are dim to negative for H3K9me2 (white arrow) (n = 1 embryonic testis at day 49, n = 2 technical replicates). Scale bar, 10 μm.
(F) Identification of overlapping and distinct genes enriched or depleted >3-fold in rhesus or human PGCs relative to undifferentiated hESCs or riPSCs. See also and .
(G) Heatmap of diagnostic genes that discriminate PGCs as being early, late, or advanced, as well as genes that are found in primate spermatogonial stem cells (SSCs) or PSCs. See text for additional details.

Rhesus and Human PGCs Are Transplantable
(A) Xenotransplantation of Carnegie stage 23 rhesus testis cells leads to colonies in the seminiferous tubules (n = 4 pairs of embryonic testis).
(B) Quantification of typical colonies following rhesus embryonic testis xenotransplantation. Error bars show the average of technical replicates and SEM.
(C) Morphology of typical rhesus colonies stained with the anti-NhP antibody, Scale bar, 50 μm.
(D) Quantification of atypical events following xenotransplantation of rhesus embryonic testes. Error bars show the average of technical replicates and SEM.
(E) Morphology of an atypical rhesus event stained with the anti-NhP antibody. Scale bar, 50 μm.
(F) Dissociated tubules from a busulfan-treated nude mouse testis that was xenotransplanted with donor embryonic testes. Scale bar, 1 mm.
(G) Dissociated tubules from a busulfan-treated nude mouse testis that was unmanipulated. Scale bar,= 1 mm.
(H) Xenotransplantation of human embryonic testes results in the identification of colonies (n = 3 pairs of embryonic human testes).
(I) Quantification of typical human colonies stained with the anti-NhP antibody. Error bars show average of technical replicates for n = 2 (day 74) or n = 1 (day 78) and SEM.
(J) Morphology of a typical human colony stained with the anti-NhP antibody. Scale bar, 50 μm.
(K) Quantification of atypical events stained with the ani-NHP antibody. Error bars show average of technical replicates for n = 2 (day 74) or n = 1 (day 78) and SEM.
(L) Morphology of an atypical human event stained with the anti-NhP antibody. Scale bar, 50 μm. Error bars show average of technical replicates and SEM.