Embryonic stem cells (ESCs) of nonhuman primate are important tools for human gametogenesis research. Generally, ESCs, embryos, and fetuses of nonhuman primates are similar to these of human. Recently, germ cell formation of mouse ESCs in vitro has been reported. In this study, we established new cynomolgus monkey ES (cyES) lines and determined germinal competency by assessing expression of mRNA markers. CyES lines were established using blastocysts produced by intracytoplasmic sperm injection (ICSI). For inducing super-ovulation, females were treated with 25 IU/kg pregnant mare serum gonadotropin (PMSG) once a day for 9 days, followed by 400 IU/kg hCG. Oocytes were collected 40 h after injection of hCG. After sperm injection, embryos were cultured in mCMRL medium to the blastocyst stage. For ES line establishment, inner cell masses (ICMs) were isolated by immunosurgery. ESC colonies emerged at about 10 days after ICM plating; three cyES cell lines were successfully obtained (3/11; 27.3%). We characterized these lines by immunocytochemistry for Oct-3/4, SSEA-3, and SSEA-4, which are diagnostic markers for primate ESCs, and by assay for alkaline phosphatase (ALP) activity. All cell lines expressed Oct-3/4, SSEA-4 and ALP activity. The previously reported SSEA-3 weak expression in cyES cells was not observed. These lines differentiated spontaneously when they were replaced in non-adherent culture (embryoid body: EB) or injected into SCID mice subcutaneously. To assess germ cell competency in vitro, we analyzed for the presence of vasa mRNA which shows a restricted expression pattern to germ cell formation, and DMC1 and SYCP1 which show specific existence on synaptonema complex in meiosis. Detection of these germ cell markers was performed by RT-PCR with total cDNA from ESCs and EBs. Nanog mRNA was detected only in ESCs. Oct-4 was detected in gonadal tissue of both sexes, ESCs, and EBs. Vasa was expressed in testis, but not in ESCs or somatic cells. Interestingly, we recognized weak expression of Vasa in Day 12-16 EBs. DMC1 and SYCP1 as meiosis markers were not detected. Because Oct-4 and Vasa mRNA are transcribed simultaneously, similar to that in the early part of gametogenesis such as the latter period of primordial germ cell (PGC) migration, PGC formation in cynomolgus EBs could occurr as in some cases of mouse or human EBs previously reported. Although detailed properties such as the functions of these Vasa-positive cells have not been confirmed, these results demonstrate that cyES cells obtained in the current study might contribute to putative germ cells in vitro by differentiating to EBs.
This study was supported by a Grant-in-Aid for the 21st Century COE Program of the Japan Mext and by a grant for the Wakayama Prefecture Collaboration of Regional Entities for the Advancement of Technology Excellence of the JST.
Drosophila argonaute-2 is required early in embryogenesis for the assembly of centric/centromeric heterochromatin, nuclear division, nuclear migration, and germ-cell formation