Generating oocytes from cells derived from skin in vitro may provide a valuable model for identifying factors involved in germ cell formation and oocyte differentiation. In addition, the "oocytes" produced could potentially be useful for therapeutic cloning, and thus offer new possibilities for tissue therapy. We recently reported the differentiation of cells derived from porcine fetal skin into cells resembling germ cells and oocytes. A subpopulation of these cells expressed germ cell markers and formed aggregate like oocyte-cumulus complexes that secreted ovarian steroid hormones and responded to gonadotropin stimulation. Some of these aggregates extruded large oocyte-like cells that expressed markers appropriate to oocytes. We now show further evidence of germ cell marker expression during differentiation. We have also compared the oocyte-like cells with natural oocytes for their expression levels of Oct4, growth differentiation factor-9b (GDF9b), the deleted in azoospermia -like (DAZL) gene, vasa, zona pellucida (ZP), and the meiosis marker synaptonemal complex protein 3 (SCP3), and have revealed interesting similarities and differences.