Cross-Species Insights into In Vitro Maturation Defects of the Oocyte and Identification of Crucial Regulators for Sheep Oocyte Maturation

The poor quality of oocytes matured <i>in vitro</i> seriously hinders the application in mammalian assisted reproductive technology (ART). Exploring the regulators and mechanisms influencing oocyte maturation is critical to improve the developmental competence of <i>in vitro</i> matured oocytes and the efficiency of ART. Here, through comparative cross-species transcriptomic analyses, we reveal that impaired autocrine/paracrine signaling and disruption of ubiquitin-dependent protein catabolic process, which are often accompanied by severe endoplasmic reticulum stress, represent common potential defects during <i>in vitro</i> oocyte maturation. Moreover, we identified two previously unrecognized key factors missing in the current IVM system by ligand screening. We further determined that EFNA1 and NRXN1 alleviated the excessive accumulation of protein aggregates and endoplasmic reticulum stress by enhancing the oocyte antioxidant defense and maintaining lipid homeostasis, thereby improving the oocyte developmental potential. Our findings identified critical extrinsic regulators of oocyte developmental competence and provided a practical strategy to improve IVM efficiency in ART.