(62) Transcriptomic Analysis Reveals Distinct Molecular Signatures in Cumulus Cells from In Vivo Matured Equine Oocytes

Kazuki Takahashi¹, Alejandro de la Fuente¹, Jamie K. Norris¹, Stuart Meyers², Robert Foss³, Pouya Dini¹  

1. Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
2. Department of Anatomy, Physiology & Cell Biology, School of Veterinary Medicine, University of California, Davis, Davis, California, USA  
3. Equine Medical Services Inc., Columbia, Missouri, USA


Abstract Text:

Demand for the in vitro production (IVP) of equine embryos is increasing. However, one of the biggest challenges regarding the IVP of equine embryos is the low rate of in vitro maturation (IVM) of oocytes. This often leads to low developmental competency of in vitro derived embryos. Oocyte maturation involves complex interactions between the oocyte and surrounding cumulus cells, which play essential roles in providing metabolic and signaling support. This study utilized bulk RNA sequencing (RNA-seq) to compare gene expression profiles of cumulus cells derived from in vivo matured, in vitro matured (using three different media), and immature equine oocytes to identify transcriptional differences and potential markers of oocyte competence. Cumulus cells were isolated from individual oocytes following in vivo maturation, IVM with three different media, and from immature oocytes. RNA-seq was performed to assess differentially expressed genes (DEGs). Genes with a fold-change >2 and adjusted p-value < 0.05 were considered significantly expressed. Bioinformatic analyses identified significant high expression of a total of 40 DEGs. These included 16 non-coding RNAs and 24 genes in cumulus cells from in vivo matured oocytes compared to all IVM groups, regardless of the media used. Key findings include elevated levels of multiple genes such as HSD3B2 and DHCR7 indicating enhanced progesterone and estrogen biosynthesis critical for oocyte maturation. FABP5, FAM13A and SYT4 showed higher expression, suggesting improved metabolic support in vivo. Higher expression of PARG indicated more efficient DNA repair mechanisms, potentially reducing genomic stress, and enhancing oocyte competence. The high expression of DPPA2 and LARGE1, which are important for female fertility in mice, may explain the improved competence of embryos in vivo. The transcriptional profile of cumulus cells from in vivo matured equine oocytes indicates a more robust hormonal and metabolically active environment compared to those derived from IVM or immature oocytes, irrespective of the IVM medium used. Elevated expression of genes involved in steroidogenesis, metabolic dynamics, and DNA repair suggests the importance of these pathways in oocyte maturation. These findings provide insight into potential molecular targets for optimizing IVM protocols to better mimic the natural maturation environment and improve oocyte developmental potential.