Cultivating a Support Network: Granulosa Cells and

Maintaining and restore the full developmental competence of either mature or immature oocytes after cryopreservation processes to preserve women fertility is a goal in assisted reproductive technologies (ART). This goal arises from the need of some patients to preserve their oocytes before arriving to a reproductively mature age, such as patients who need to undergo chemotherapy. Although in vitro fertilization (IVF) can be performed to store embryos for future use with cumulative pregnancy rates >60% [1], this may not be an option for single women or patients without time to complete ovarian stimulation prior to cancer therapy. For those patients, oocyte cryopreservation can be considered instead [1-4]. Data from 21 peer-reviewed journals show that mean survival rate of frozenthawed mature oocytes is 47%, while mean fertilization rate is 52.5% with a mean pregnancy rate for thawed oocytes of only 1.52% [1]. It has been suggested that immature oocytes may be more resistant to cryodamage due to lower cell volume and lack of metaphase spindle. Even though high rates of nuclear maturation have been reported with cryopreserved immature oocytes instead [1,3], the developmental capacity has been generally low [1]. The processes involved in oocyte maturation includes resumption of meiosis form prophase I, when the oocyte is in Germinal Vesicle stage (GV), to the extrusion of the first polar body, in Metaphase II (MII); the expansion of somatic cells surrounding the oocyte and the maturation of the cytoplasm to support fertilization and early embryonic development [5]. Whether the maturation happens in vivo or in vitro, the environment to which the oocyte and its surrounding cells are exposed, affects the developmental competence of the oocyte and subsequent embryonic development [5]. Oocytes within the ovarian follicle are surrounded by mural and cumulus granulosa cells, which perform both endocrine and developmental functions, respectively. The coordinate function of both granulosa cell types is necessary to fulfill oocyte requirements. A critical difference between cryopreserving MII or GV stage oocytes centers on the importance of the intercellular contacts between germinal and somatic cells. MII-stage oocytes do not rely on support from surrounding somatic cells, while cryopreservation of GV-stage oocytes requires maintenance of their communication with viable somatic cells to preserve a mutual interaction [4]. In both cases, being able to reproduce the