Spermatogonial stem cell in fish: physiology, transcriptomics and biotechnological application

We have previously found several unique characters of germ cell development using rainbow trout.  These are 1) spermatogonia transplanted into peritoneal cavity of newly hatched larvae migrated towards recipient gonads, probably by chemotaxis, 2) spermatogonia transplanted into female recipients started oogenesis and finally produced functional eggs, 3) triploid trout develop and grow normally but their germ cells cannot complete gametogenesis. By combining these unique characteristics of fish germ cells, in this study, we established a xenogeneic transplantation system of spermatogonia in salmonid fish. Spermatogonia isolated from mature testes of vasa-Gfp transgenic rainbow trout were transplanted into the peritoneal cavity of triploid masu salmon hatchlings. The transplanted trout spermatogonia migrated towards the recipient salmon genital ridges with extending pseudopodia and were subsequently incorporated into them.  We further confirmed that the donor-derived spermatogonia resumed gametogenesis and produced sperm and eggs in male and female salmon recipients, respectively.  By insemination of the resulting eggs and sperm, we got only rainbow trout offspring in the F1 generation, suggesting that the triploid salmon recipients produced functional gametes derived only from donor trout.  One obvious outcome is application to bluefin tuna production.  Since broodstock of bluefin tuna is quite large (>100kg) and difficult to maintain in captivity, if we can generate surrogated mackerel that can produce tuna gametes, seed production of bluefin tuna would be much easier.  Currently, we have been working on “tuna-mackerel” experiments and application of transcriptome technology to characterize fish germ cells.  These data will also be introduced in this symposium.