Differentiation of germ cells and gametes from stem cells

Advances in stem cell research have opened new perspectives for regenerative and reproductive medicine. Stem cells (SC) can differentiate under appropriate in vitro and in vivo conditions into different cell types. Several groups have reported their ability to differentiate SCs into germline cells, and some of them have been successful in obtaining male and female gamete-like cells by using different methodologies. This review summarizes the current knowledge in this field and emphasizes significant embryological, genetic and epigenetic aspects of germ cells and gametes in vitro differentiation in humans and other species, highlighting major obstacles that need to be overcome for successful gametogenesis in culture: studies reporting development of germ cell-like cells from murine and human embryonic (ESC) and somatic SCs are critically reviewed. Published studies indicate that germ cells can be consistently differentiated from mouse and human ESC. However, further differentiation of germ cells through gametogenesis still has important genetic and epigenetic obstacles to be efficient. Differentiation of germ cells from SCs has the potential of becoming a future source of gametes for research use, although further investigation is needed to understand and develop the appropriate niches and culture conditions. Additionally, if genetic and epigenetic methodological limitations could be solved, therapeutic opportunities could be also considered.