Stem cells and the reproductive system: historical perspective and future directions

Recent findings in stem cell biology have presented new perspectives and opportunities for the treatment of reproductive disease. In a departure from the long held dogma of embryologically fixed numbers of oocytes, current literature suggests that human ovaries contain stem cells which form new oocytes even in adulthood and that these stem cells can be cultured in vitro to develop into mature oocytes. These findings have provided new hope and broader options for fertility preservation. Evidence of endometrial regeneration by bone marrow stem cells in endometrial tissue of women who received bone marrow transplant highlight potential for the novel treatments of uterine disorders and supports new theories for the etiology of endometriosis - ectopic transdifferentiation of stem cells. Further, endometrial derived stem cells have been demonstrated to be useful in the treatment of several chronic and often debilitating diseases, including Parkinson's Disease and Diabetes. Other cells that may present future therapeutic benefits for a myriad of disease states include placental and fetal cells which enter maternal circulation during pregnancy and can later promote parenchymal regeneration in maternal tissue. These findings highlight novel functions of the uterus and ovaries. They demonstrate that the uterus is a dynamic organ permeable to fetal stem cells capable of transdifferentiation as well as a renewable source of multipotent stem cells. While we still have much to understand about stem cells, their potential applications in reproductive biology and medicine are countless.