TRANSCRIPTOME LANDSCAPE OF EARLY FOLLICULOGENESIS IN MAMMALS: UNLOCKING THE INTERPLAY MECHANISMS TO ENHANCE ART EFFICIENCY IN FERTILITY PRESERVATION

Assisted reproductive technologies (ARTs) are fundamental in fertility preservation. However, current ART procedures rely only on a limited portion of the female gamete reserve, specifically the antral follicles. In contrast, the preantral follicle population, which represents 99% of the reserve, remains unexploited. To date, no established culture system has been successfully adopted to replicate folliculogenesis in vitro, as existing approaches remain experimental due to an incomplete understanding of the mechanisms involved, thus limiting the success of mimicking the complete folliculogenesis process in vitro. Folliculogenesis is a highly regulated process. From the formation of primordial follicles, several pathways intervene to control their different fates: they can remain dormant, activate, or undergo programmed cell death. Morphological and functional changes occur within the follicles, which interact with the ovarian stromal environment, particularly the ovarian cortex. The ovarian cortex surrounds the preantral follicles and mediates dialogue through paracrine biochemical signaling pathways to sustain the development of primordial, primary, and secondary follicles. The current research highlighted the significance of a strategic framework to exploit the ovarian preantral follicle population in the bovine species as a model, beginning with developing an isolation protocol for preantral follicles based on tissue quantity and age. This tool paved the way for isolating follicles suitable for downstream analysis to unravel key regulators and pathways involved in the follicle stage differentiation. Profiling the transcriptome of primordial, primary, and secondary follicles provided tools to identify stage-specific mechanisms that characterize follicle development. Moreover, examining the interplay between the germinal and somatic follicle compartments introduced key elements to clarify the intimate crosstalk within each differentiation stage. Finally, appropriately tailoring a culture system requires a comprehensive understanding of the surrounding microenvironment and its interactions with the follicles. With this in mind, we explored metanalysis approaches to dissect the pathways involved in the interactions between the follicular parenchymal and stroma. This thesis examines fertility preservation from multiple perspectives: a qualitative and quantitative approach to describing follicular classes and maximizing the exploitation of the ovarian reserve based on tissue volume and age. Furthermore, the study places significant emphasis on a mechanistic approach to identifying the pathways leading to each follicular stage to enable the development of a culture system tailored to the specific needs of individual follicles. This will boost the efficiency of fertility restoration in ART applications in clinical settings, animal breeding, and biodiversity preservation efforts for endangered species.