Postnatal oogenesis in humans: a review of recent findings

Abstract

In spite of generally accepted dogma that the total number of follicles and oocytes is established in human ovaries during the fetal period of life rather than forming de novo in adult ovaries, some new evidence in the field challenges this understanding. Several studies have shown that different populations of stem cells, such as germinal stem cells and small round stem cells with diameters of 2 to 4 μm, that resembled very small embryonic-like stem cells and expressed several genes related to primordial germ cells, pluripotency, and germinal lineage are present in adult human ovaries and originate in ovarian surface epithelium. These small stem cells were pushed into the germinal direction of development and formed primitive oocyte-like cells in vitro. Moreover, oocyte-like cells were also formed in vitro from embryonic stem cells and induced pluripotent stem cells. This indicates that postnatal oogenesis is not excluded. It is further supported by the occurrence of mesenchymal stem cells that can restore the function of sterilized ovaries and lead to the formation of new follicles and oocytes in animal models. Both oogenesis in vitro and transplantation of stem cell-derived “oocytes” into the ovarian niche to direct their natural maturation represent a big challenge for reproductive biomedicine in the treatment of female infertility in the future and needs to be explored and interpreted with caution, but it is still very important for clinical practice in the field of reproductive medicine.

In Vitro Generation of Oocytes from Ovarian Stem Cells (OSCs): In Search of Major Evidence

“…Two distinctive opinions concerning oogenesis were raised in the last 50 years, first by Waldeyer and his group who claimed that before and after birth, oocytes originate from ovarian germinal epithelium [1], whereas Beard and coworkers proposed that all oocytes are generated during the embryonic time before the birth and thus are exhaustively utilized until menopause [2]. Subsequently, other investigators described the existence of OSCs in the adult mammalian ovary that are expected to undergo neo-oogenesis and differentiate into OLCs either spontaneously or under proper culture conditions [3,4].…”

The Effect of Folic Acid Supplementation in the Ovary and Upon Embryo Development

“…The primary oocyte does not complete meiosis I, but stops at the first meiotic prophase division; this stage is referred to as the germinal vesicle. However, it is not until puberty when primary follicles will continue to grow and be recruited during each cycle (a term known as primordial follicle recruitment), and only one oocyte (in human) from the dominant follicle matures and will be ovulated (Virant-Klun, 2015).…”

Descriptive and functional definition of nucleolus – a pathway to cancer therapy

“…Jezgrica sadrži kompetentne i nekompetentne nukleolarne organizatore. Kompetentni su NOR-i koji su aktivni u profazi 102,103 . Broj ribosomalnih gena svojstvo je koje se nasljeđuje.…”