The Changes In Nuclear Morphology Of Porcine Oocyte Derived From Early Antral Follicle During In Vitro Growth

Abstract

Female patients of infertility may benefit from an abundant supply of oocytes derived from early antral follicles (1-1.5mm) if provided with the appropriate culture conditions to induce growth and maturity of the oocytes at a reliable rate. Pigs are often chosen as animal models for research in reproduction due to the physiological similarities to human subjects. However, the relationship between chromatin configuration and development of follicles during the in vivo growth process has not been clear. This study aims to document the changes in chromatin configuration and oocyte diameter under natural conditions and compare the changes in chromatin configuration and diameter of oocytes cultured under in vitro growth medium against the development under in vivo conditions. The aceto-orcein staining method was used to visualize the chromatin morphology of oocytes collected from porcine follicles of various sizes (0.1mm to less than 6mm). In addition, immunostaining was used to highlight the changes in chromatin configuration of oocytes from oocytes derived from early antral follicles (1-1.5mm) and fully grown follicles (4-6mm) after IVM. The study found that the size of oocytes from early antral follicles after incubating in IVG medium for 4 days had grown to nearly the size of oocytes found in fully grown follicles (119.6mm) while the proportion of chromatin morphology at 4 stages (FC, SC, GV, spontaneous maturation) more closely resembled oocytes from 3-4mmm follicles. Once the oocytes from early antral follicles and fully grown follicles had undergone IVM, it was found that most of the oocytes from early antral follicles did not reach metaphase I, and the oocytes that were successfully formed a larger percentage in the group compared to those from fully grown follicles (19.6%>14.0%). The findings suggest the EAF-derived oocytes under in vitro culture were able to produce sufficient nutrients to achieve the size of mature oocytes but could not secrete enough growth factors to effectively gain meiotic competence. Supplementation of specific factors and the extension of culture time were suggested to increase the output of mature oocytes.