Integrated molecular analysis of granulosa cells and follicular fluid extracellular vesicles reveals predictive biomarkers of oocyte maturation in the southern white rhinoceros

Abstract

Introduction Assisted reproductive technologies (ARTs) are an imperative conservation tool to rescue species from extinction. An essential step towards technological advancements and ARTs’ successes is identifying optimal in vitro culture conditions to mature oocytes, carry out fertilization, and culture embryos for future transfer. The role of follicular fluid-derived extracellular vesicles (FF-EVs) and granulosa cells (GC) in follicular development, oocyte maturation, and fertilization has been extensively studied for decades in human and domestic species models. Methods This study aimed to identify transcriptomic differences in GC mRNA and miRNA expression, as well as miRNA cargo in FF-EVs in the southern white rhinoceros (SWR), and to integrate these datasets to uncover coordinated regulatory networks associated with oocytes that matured (with polarbody, PB) compared to those that failed to mature (without polar body, NoPB) following in vitro maturation. Results Overall, in GCs, 1,117 transcripts (including both annotated and unannotated) were differentially expressed between groups. In GC-derived miRNAs, 11 were differentially expressed, all of which were upregulated in the PB group. In FF- EV samples, 15 miRNAs were identified as differentially expressed between the two groups. Comparison of predicted miRNA targets with the differentially expressed genes revealed multiple overlapping genes, suggesting a coordinated post-transcriptional regulation mechanism. Discussion These miRNA-mRNA interactions are potential targets for further investigation, both as potential modulators to improve in vitro maturation outcomes and as biomarkers for predicting oocyte maturation potential in the SWR. In conclusion, the EV–mediated mRNA-miRNA signaling occurring during folliculogenesis in the SWR may offer critical insights into physiological reproductive conditions that contribute to oocyte maturation, ultimately informing the development of novel reproductive strategies to enhance ART outcomes in this species and others.