Parthenogenetic Embryo-Like Structures in the Human Ovarian Surface Epithelium Cell Culture in Postmenopausal Women with No Naturally Present Follicles and Oocytes

Little is known about parthenogenesis in the human ovary. What is known is related to patients with teratoma in their medical history. Ovarian surface epithelium (OSE) was often proposed as a source of ovarian stem cells with an embryonic character in the past, and was also termed "germinal epithelium." The aim of this study was to isolate putative stem cells from OSE scrapings, to set up an OSE cell culture, to follow the in vitro oogenesis and possible formation of parthenogenetic embryos in 21 postmenopausal women with no naturally present follicles and oocytes. Small round cells with a bubble-like structure and with a diameter from 2 to 4 mu m were isolated from the material obtained by OSE scrapings in all women. They expressed early embryonic developmental markers such as stage- specific embryonic antigen-4 (SSEA-4) surface antigen and Oct-4, Nanog, Sox-2, and c-kit transcription factors. These cells were separated by density gradient centrifugation and grown in vitro, where they proliferated and formed embryoid body-like structures. Their markers of pluripotency such as telomerase activity were decreased during in vitro culture and they did not form teratoma after the injection into SCID mice. Some of them grew intensively and reached a diameter of approximately 20 mu m after 5-7 days of culture. In the OSE cell culture, oocyte-like cells developed among them, which reached a diameter up to 95 mu m, and expressed Oct-4, c-kit, VASA, and ZP2 transcription markers after 20 days of culture. Some of them expressed a zona pellucida-like structure and rarely germinal vesicle- and polar body-like structures. At the same time, parthenogenetic blastocyst-like structures developed, which expressed transcription markers Oct-4, Sox-2, and Nanog and were normal for chromosomes X, Y, 13, 16, 18, 21, and 22. In conclusion, the discovered cells expressed embryonic stem cell markers, gave rise to embryoid body-, oocyte-, and blastocyst-like structures, and might be involved in the human reproduction and formation of ovarian tumors.