CORTICAL GRANULES ANALYSIS IN POSTOVULATORY AGED OOCYTES

WETTEN, PA; KLINSKY LAHOZ, OG; MICHAUT, MA

Salta

Congreso; Joint LV Annual SAIB Meeting and XIV PABMB Congress; 2019

Once oocytes are ovulated, there is a time window in which they are normally fertilized. After this period of time, those non fertilized oocytes will decrease their quality leading to postovulatory aging. Postovulatory oocyte aging can occur at any age of a fertile female´s life and during oocyte manipulation in assisted fertilization treatments. Cortical granule exocytosis (CGE), also referred as cortical reaction, is a secretory process triggered by sperm-oocyte fusion during fertilization and is involved in blocking polyspermy. Although it is known that aging produces a decrease in fertilization rate and increase the polyspermy, there is no evidence about cortical granule density in postovulatory aged oocytes. Therefore, the aim of this research was to analyse cortical granules density in postovulatory aged oocytes. Two models of postovulatory aging were tested -in vitro and in vivo aged oocytes- and compared with control condition. To obtain in vitro aged oocytes, mature oocytes were collected from hormonally stimulated female mice 16 h post hCG injection (control) and were in vitro incubated for 4 and 8 hs. To obtain in vivo aged oocytes, mature oocytes were collected from hormonally stimulated female mice 20 and 24 h post hCG. Results showed that cortical granules density was decreased in both postovulatory aged oocytes when compared to control cells. Secretion of cortical granules was confirmed by staining and quantification of exudate dots. Next, because secretion of cortical granules is a calcium-dependent process, we determined calcium cytoplasmic level using Fura2-AM. We found that in both conditions of aging, the basal calcium level diminished compared to the control oocytes. Previous findings have reported that cortical granules are immersed in an actin network in the cortical region, so we explored actin localization in aged and control oocytes. Control oocytes presented a cortical actin localization whereas aged oocytes, in both conditions, showed cortical and cytoplasmic actin localization. Altogether, our results suggest that postovulatory aging affects the physiology of cortical granules in mouse oocytes.