Vitrification preserves follicular transcriptomic dynamics during ex vivo ovulation
Vitrification is a method for long-term biological sample cryopreservation without causing intra- and extra-cellular ice formation. We recently established a novel closed vitrification system to cryopreserve mouse ovarian follicles. Using the 3D alginate hydrogel encapsulated in vitro follicle growth (eIVFG) method, we have demonstrated that compared to freshly-harvested follicles, vitrified follicles have normal follicle and oocyte reproductive outcomes. Our recent study further demonstrated the faithful preservation of molecular signatures of follicle-stimulating hormone (FSH)-stimulated follicle maturation in vitrified follicles. However, it is unknown whether ovulation, another crucial gonadotropin-dependent follicular event, and involved ovulatory gene regulatory pathways are well conserved in vitrified follicles. Fresh and vitrified follicles grown for 8 days by eIVFG were collected at 0, 1, 4 and 8-hour post human chorionic gonadotropin (hCG) treatment for the single-follicle RNA sequencing. Principal component analysis (PCA) and Pearson's correlation analysis revealed that vitrified follicles have similar transcriptomic profiles to fresh follicles. Furthermore, the expression of several genes essential for ovulation were comparable between vitrified and fresh follicles. In summary, these results demonstrate that our closed vitrification system preserves follicular transcriptomic dynamics during ex vivo ovulation. Together with our previous findings that vitrification preserves FSH-stimulated follicle maturation, the integration of vitrification of immature follicles and eIVFG has a great potential to serve as an additional fertilization preservation approach for young cancer patients and endangerers species. Moreover, follicle vitrification enables a high-content ovarian follicle biobank, which can greatly improve the throughput of eIVFG for studying ovulation biology, anovulatory disease, toxicology, and novel contraceptive drug development targeting ovulation. Overall design: Fresh and vitrified follicles grown for 8 days by eIVFG were collected at 0, 1, 4 and 8-hour post human chorionic gonadotropin (hCG) treatment for the single-follicle RNA sequencing