NEDDylation maintains oocyte quality by stabilizing mitochondrial transcription

Age-related decline in oocyte quality increases the risk of infertility, miscarriage, and birth defects. Mitochondrial dysfunction is a key contributor to this decline. Here, we report that oocyte-specific deletion of Uba3, which encodes the catalytic subunit of the E1 NEDDylation-activating complex, causes sterility in mice. Fully grown, germinal vesicle-stage Uba3 conditional knockout oocytes exhibit mitochondrial dysfunction, including elevated reactive oxygen species, impaired oxidative phosphorylation, and depletion of mitochondrially encoded RNA transcripts. Proteomic analysis identified alterations in mitochondrial-associated proteins, including enrichment of mitochondrial matrix and respiratory chain components and reduced abundance of electron transport chain complexes. These defects were associated with reduced levels of the mitochondrial RNA polymerase, POLRMT [polymerase (RNA) mitochondrial DNA directed]. We further show that POLRMT is directly modified by NEDDylation, which alters its stability by antagonizing ubiquitylation and degradation. Notably, NEDD8 levels decline with age in both mouse and human oocytes. Together, these findings identify NEDDylation as a regulator of oocyte quality and connect this pathway to mitochondrial transcription in oocytes.