Selection of competent oocytes for assisted reproductive technologies

Oocyte competence or quality have defined as the ability of oocyte to resume meiosis, cleave following fertilization, develop and differentiate into blastocyst stage, induce pregnancy and finally bring healthy offspring. Oocyte maturation is one of the most important processes of oogenesis, since it leads to the generation of “competent fertilizable oocytes”. Oocyte maturation include nuclear maturation, cytoplasmic maturation, and Epigenetic maturation which is precisely regulated by molecular factors. Invasive and noninvasive methods are commonly used to select developmentally competent oocytes that can improve the take‐home baby rates in assisted reproductive technology (ART) centers. One of the noninvasive methods conventionally utilized to determine competent oocytes is the morphological analysis of cumulus complex, first polar body, zona pellucida, perivitelline space, meiotic spindle, and ooplasm. however, all morphological criteria that are currently used for the grading and screening of oocytes are not able to eliminate the subjectivity. Despite recent studies of the molecular factors related to oocyte quality, it is technically difficult to develop an index based on these factors, and new indices that reflect intracellular conditions are necessary. The numerous transcriptomics, proteomic and metabolomic studies have been conducted in the follicular fluid and follicular cells (granulosa and cumulus cells) in order to find non-invasive biomarkers of oocyte quality. Recent studies have uncovered the presence of cell-secreted vesicles in follicular fluid. Moreover, these cell-secreted vesicles contain small non-coding regulatory RNAs called microRNAs, which can be shuttled between maturing gametes and surrounding somatic cells. In humans, it is known that extracellular microRNAs of follicular fluid are associated with fertilization ability and early embryo quality. Recently, oocyte condition can be evaluated noninvasively using a temperature imaging system. The dynamic changes in the cytoskeleton and mitochondrial activity are considered to contribute to intracellular thermal variations. Intracellular temperature in mature oocytes was higher in fresh oocytes immediately after PB۱ extrusion, and the temperature decreased with time after polar body release. The differences in oocyte intracellular temperature can correlate with developmental competence. Fresh oocytes had high‐temperature regions localized around the cell membrane and around the spindle. Further studies should evaluate the link between temperature and cellular phenomena to establish its use as an indicator of quality.

کلیدواژه ها:

Oocyte quality ، oocyte maturation ، follicular fluid ، microRNA ، temperature