Recent progress in embryonic stem cell research and its application in domestic species.

Many reports described cell lines derived in domestic species, which presented several important features typical of embryonic stem cells (ESCs). Such features unfortunately did not include the capacity to generate germ-line chimeras, therefore limiting the possibility to use these cells as tools for the genetic manipulation. However, farm animal ESCs may still be useful for the generation of transgenic animals as usually have a self-renewal capacity more prolonged than normal primary cultures thus increasing the possibility to transform and select cells to be used as nucleus donors in cloning procedures. Farm animal ESCs may also be an excellent experimental model in pre-clinical trials, assessing the feasibility of cell therapy because of the close morphological and physiological resemblance to humans of species like the pig. However, the persistent lack of standard methods for the derivation, maintenance and characterization of ESCs in domestic species stimulated the search for alternatives. Embryonic germ cells may represent such an alternative. Indeed, these cells showed a higher plasticity than ESCs as contributed to embryonic development forming chimeric newborns but, as for ESCs, standardization is still far away and efficiency is very low. Recent results indicated spermatogonial stem cells as possible tools for germ-line genetic modifications with some proof of principle results already achieved. But, a real break through could arrive from the multipotent germ-line stem cells, virtually equivalent to ESC, derived from newborn and adult mouse testis.