Production of juvenile masu salmon (Oncorhynchus masou) from spermatogonia-derived sperm and oogonia-derived eggs via intraperitoneal transplantation of immature germ cells.

No effective cryopreservation technique exists for fish eggs and embryos; thus, the cryopreservation of germ cells (spermatogonia or oogonia) and subsequent generation of eggs and sperm would be an alternative solution for the long-term preservation of piscine genetic resources. Nevertheless, in our previous study using rainbow trout, we showed that recipients transplanted with XY spermatogonia or XX oogonia produced unnatural sex-biased F1 offspring. To overcome these obstacles, we transplanted immature germ cells (XX oogonia or XY spermatogonia; frozen for 33 days) into the body cavities of triploid hatchlings, and the transplanted germ cells possessed a high capacity for differentiating into eggs and sperm in the ovaries and testes of recipients. Approximately 30% of triploid recipients receiving frozen germ cells generated normal salmon that displayed the donor-derived black body color phenotype, although all triploid salmon not receiving transplants were functionally sterile. Furthermore, F1 offspring obtained from insemination of the oogonia-derived eggs and spermatogonia-derived sperm show a normal sex ratio of 1:1 (female:male). Thus, this method presented a critical technique for practical conservation projects for other teleost fish species and masu salmon.

Mature oocytes derived from purified mouse fetal germ cells.

BACKGROUND: Mouse fetal germ cells have been successfully purified from fetal gonads. However, there are no published reports describing a procedure for deriving mature oocytes from isolated fetal germ cells. The purpose of this present study is to explore whether purified fetal germ cells are able to differentiate into mature oocytes through an in vivo grafting procedure. METHODS AND RESULTS: First, intact 11.5 and 12.5 days post-coitum (dpc) female gonads with or without the attached mesonephros and the reaggregated female gonad cells were transplanted into the recipient mice. The results demonstrate both the gonad accompanied by mesonephroi and the innate gonad structure are not absolutely required for 11.5 dpc and 12.5 dpc oogonia to generate mature oocytes. Next, oogonia were purified from female gonads, aggregated with different ovarian somatic cells and transplanted into the recipient mice. Purified 12.5 dpc oogonia were able to generate mature oocytes by aggregating with 12.5 dpc ovarian somatic cells, but not with 16.5 dpc or 0 days postpartum ovarian somatic cells. We also tested 12.5 dpc male germ cells but they were unable to undergo oogenesis. CONCLUSIONS: Our study demonstrates that mature oocytes can be derived from purified fetal germ cells through an aggregation and transplantation procedure. It also suggests that the synchronized interactions between oogonia and gonadal somatic cells are important to ensure normal folliculogenesis.