Reproduction Abstracts

Introduction: Testicular tumors not only facilitate analyses of tumorigenesis in testes but also are a good resource for culturing spermatogonial stem cells (SSCs) that allow us to manipulate genetic modification. In zebrafish, a hypertrophied tumorous testis happens to be found occasionally, but no method for maintenance of the individual tumorous testis has prevented systematic analyses of the characters and the practical use. We describe here the method for maintenance of testicular tumors by subcutaneous grafting into an immunodeficient mutant zebrafish.

Materials and methods: Three independent tumorous testes were isolated from different lines. The testis was dissected into five to ten small fragments that contained outer layer of the testis, and then transplanted under the abdominal skin of mutant fish. Recipient fish were reared in fish water containing antibiotics for 4 days, and then maintained normally.

Results and discussion: Almost all recipient fish survived more than 1 month, and tumorous testes grew under the abdominal skin. Some of them survived more than 1 year. After growth of tumorous testes as same as the original size, we removed them and repeated dissection and transplantation. Histological analyses revealed that two of three tumorous testes maintained SSCs and the testicular structure while one testis lost them after successive transplantations. In in vitro cultures, SSCs from the two testes grew without any abnormality. These results suggest that testicular tumors can be maintained and amplified by subcutaneous grafting in the immunodeficient mutant when an appropriate testicular tumor is selected in each transplantation step.