Salvaging Genetic Material from Endangered Species: Xenografting of Testis Tissue from Immature Bison and Deer Donors into Recipient Mice Results in Complete Spermatogenesis.

The purpose of this study was to evaluate the long-term outcome of testis tissue xenografting from bison and deer as models for closely-related rare or endangered ungulates. Testis tissue was collected post-mortem from 2 newborn bison calves (Bison bison bison) and a 2-mo-old white-tailed deer fawn (Odocoileus virginianus). Small fragments of donor testis tissue were grafted under the back skin of immunodeficient recipient mice (n = 15 mice for bison xenografts and n = 7 mice for deer xenografts; 8 fragments/mouse). Single xenograft samples were removed from representative recipient mice every 2 mo from grafting for up to 16 mo for bison xenografts, and 14 mo post-grafting for deer xenografts. The retrieved xenografts were evaluated for seminiferous tubular density (per mm2) and tubular diameter, as well as for seminiferous tubular morphology and identification of the most advanced germ cell type present in each tubule cross section. Overall, 69% of the grafted testis fragments from donor bison and 63% of those from donor deer were recovered as xenografts. The weight of bison testis tissue xenografts increased (P < 0.02) ~4-fold by 2 mo and ~10-fold by 16 mo post-grafting. In bison xenografts, gradual maturational changes were evident in the form of seminiferous tubule expansion starting at 2 mo, first appearance of spermatocytes at 6 mo, round spermatids at 12 mo, and elongated spermatids at 16 mo post-grafting. For bison grafts, a donor effect on efficiency of spermatogenesis was also observed. Testis tissue xenografts from donor white-tailed deer also showed a gradual testicular development starting with tubular expansion also by 2 mo and presence of spermatocytes by 6 mo post-grafting, but round and elongated spermatids by 8 mo, followed by fully-formed spermatozoa by 12 mo post-grafting. The timing of complete spermatogenesis roughly corresponds to the reported timing of sexual maturation in these species. This study demonstrated, for the first time, that testis tissue xenografting from neonatal/immature bison or deer donors into recipient mice can successfully result in testicular maturation and development of spermatogenesis in the grafts up to the stage of spermatozoa production. These results may therefore provide a model for salvaging genetic material from immature males of rare or endangered ungulates that die prematurely. (platform)