Potential and challenges of testis tissue xenografting from diverse ruminant species

In 2002, we reported that small fragments of testis tissue from immature mouse, pig or goat donors grafted in recipient mice undergo development, maturation and complete spermatogenesis, including the generation of fertilisation-competent murine, porcine or caprine sperm. Testis tissue xenografting (TTX) was then successfully applied using a range of donor species including laboratory/domestic/non-domestic animals and primates. This system offers a novel in vivo model for the study of testis function, and a previously unavailable opportunity to produce sperm in the grafts from immature donors of diverse species. The TTX model also provides easier access for experimental manipulation of the grafted testis tissue or its environment in the recipient mouse; something that is not feasible in many donor species. This application will allow analysis of, for instance, the effects of new hormone regimens, drugs or toxicants on testis function, without experimentation in the target species. Grafting of fresh or preserved testis tissue also can be used as an invaluable tool for the conservation of fertility from immature individuals of valuable or endangered animals. Reviewed here are an overview of the contributions by the author and colleagues and a critical examination of the salient literature on TTX especially using ruminant donors, as well as examples of its variety of current and potential applications for research in male reproductive biology and technologies using ruminant models. The challenges facing optimisation of TTX model as well as its field/experimental uses, along with insights and suggested remedies, are also discussed.