Recent advances for spermatogonial stem cell transplantation in livestock

At the foundation of spermatogenesis are the actions of spermatogonial stem cells (SSCs), and a remarkable feature of these cells is the capacity to regenerate spermatogenesis following transplantation into testes of a recipient male that lacks endogenous germline. This ability could be exploited in livestock production as a breeding tool to enhance genetic gain. A key element to success is derivation of culture conditions that support proliferation of SSCs to provide sufficient numbers of cells for transfer into multiple recipient males. Using methodology devised for rodent cells as a foundation, advances in culturing cattle SSCs have occurred over the past few years and efforts are underway to extend this capability to pig cells. Another critical component to SSC transplantation is generation of males with germline ablation but intact somatic support cell function that can serve as surrogate sires for donor-derived spermatogenesis in a natural mating scheme. Recent advances in pigs using gene editing technologies have demonstrated that knockout of a key male germ cell-specific gene, namely NANOS2, leads to male-specific germline ablation but otherwise normal physiology, including intact seminiferous tubules. Together with recent advances in culturing spermatogonia of higher-order mammals, the now efficient means of producing germline-ablated recipient males have brought the application of SSC transplantation in livestock as a production tool closer to reality than ever before.