49 Transcript profiles of blastocysts produced from oocytes matured in fluid from preovulatory follicles of varied maturity

Reproductive success is multi-faceted; however, the oocyte’s competency to develop into a quality embryo is necessary for pregnancy. Appropriate preparation of the oocyte to support early embryo development is heavily influenced by intercellular communication between the maturing oocyte and preovulatory follicle. Variations in preovulatory follicle maturity, as indicated by follicle estradiol production or size, have been linked to profound differences in pregnancy success, follicular fluid metabolite milieu, cumulus–oocyte metabolism, and oocyte competency for embryo development. Such relationships indicate metabolic and developmental programming of the oocyte based on follicle maturity, but the impact of preovulatory follicle maturity on the molecular signature of resulting blastocysts has not been examined. We hypothesized that supplementing IVM oocytes with follicular fluid originating from preovulatory follicles of Greater or Lesser physiological maturity would influence the transcriptome of resulting blastocysts. The objective was to investigate the impact of follicle maturity on metabolic preparation of the oocyte by examining alterations in the functional genome of resulting blastocysts. Follicular fluid was collected 18 h after a gonadotrophin releasing hormone (GnRH)-induced LH surge. Serum estradiol concentrations at GnRH administration were used to categorize follicle maturity into Greater (9.5–15.4 pg mL⁻¹) or Lesser (1.9–4.9 pg mL⁻¹) treatments. In vitro maturing oocytes were supplemented with 20% follicular fluid collected from preovulatory follicles categorized as Greater or Lesser follicle maturity. In vitro fertilization and embryo culture were performed identically between treatments, and RNA-sequencing was performed on pools of two blastocysts from each treatment (Greater, n = 12; Lesser, n = 15). One hundred thirteen transcripts differed in abundance between blastocysts of Greater and Lesser follicle maturity treatments. Differentially abundant transcripts indicated improved Wnt/β-catenin signaling, metabolism, and protection from oxidative stress in blastocysts resulting from oocytes matured in the presence of follicular fluid of preovulatory follicles of Greater maturity. Alternatively, demonstration of unregulated cell growth presented in blastocysts from oocytes of the Lesser follicle maturity treatment. Follicular fluid milieu from preovulatory follicles of Greater physiological maturity may better prepare maturing oocytes for early embryo development. Oocytes matured in follicular fluid of Lesser mature follicles appeared to overcompensate for lack of nutrients during oocyte maturation, thus leading to uncontrolled cellular growth, poorer Wnt signaling, less efficient metabolism, and increased oxidative stress.

This project was supported by Agriculture and Food Research Initiative Competitive Grant no. 2023-67015-39454 from the US Department of Food and Agriculture.