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bioRxiv2026

ER stress-associated IRE1α signalling links impaired QPRT-dependent NAD⁺ biosynthesis to reduced oocyte competence

Oocyte quality is closely linked to metabolic and organelle homeostasis, but the mechanisms underlying naturally occurring differences in oocyte quality remain incompletely understood. Here, we identify a link between endoplasmic reticulum (ER) stress, impaired NAD biosynthesis and poor oocyte quality. Poor-grade goat oocytes exhibited profound NAD depletion, accompanied by quinolinic acid accumulation and reduced expression of quinolinate phosphoribosyltransferase (QPRT), suggesting a bottleneck in de novo NAD biosynthesis. Restoring QPRT expression or bypassing this metabolic step improved meiotic maturation. Further analyses revealed altered ER stress signalling, increased IRE1-associated activity and reduced QPRT RNA stability. Recombinant IRE1 processed QPRT RNA in vitro, suggesting a possible link between IRE1 activity and QPRT transcript regulation. Supplementation with nicotinamide mononucleotide (NMN) restored NAD levels and improved several features of poor-quality oocytes, including calcium homeostasis, oxidative stress and mitochondrial membrane potential. NMN treatment also improved early embryonic development, with its beneficial effects involving SIRT6 activity and changes in DNA methylation-associated fluorescence. Importantly, NMN supplementation improved meiotic maturation in poor-grade bovine and porcine oocytes, indicating that this metabolic intervention may have broader relevance across mammals. Analysis of published human oocyte proteomic data further revealed age-associated changes in ER proteostasis and NAD-related proteins. Together, our findings identify ER stress-associated disruption of QPRT-dependent NAD biosynthesis as a potential contributor to poor oocyte quality and suggest that restoring NAD metabolism may offer a strategy to improve the functional properties of compromised oocytes.

cell biology↗

bioRxiv2026

HIPK2-and IKKβ-dependent phosphorylation stabilizes TAp63α during the oocyte DNA damage response

TAp63, a member of the p53 family, serves as a central quality control factor in oocytes, safeguarding genomic integrity during the prolonged dictyate arrest of meiosis. In healthy oocytes, TAp63 is maintained in an inactive dimeric state; upon DNA damage, it undergoes phosphorylation-dependent tetramerization, enabling transcriptional activation of pathways that determine oocyte fate. While the upstream activation cascade of TAp63 has been well characterized, the mechanisms that regulate its stability during the DNA damage response remain incompletely understood. Here, we identify the kinases HIPK2 and IKK{beta} as key regulators of TAp63 stability. We show that TAp63 interacts with both kinases and is phosphorylated at distinct residues, T452 by HIPK2 and S4/S12 by IKK{beta} in vitro and in vivo, in addition to previously described CHK2 and CK1-mediated phosphorylation. Functionally, these phosphorylation events do not primarily contribute to activation, but instead stabilize TAp63 by limiting MDM4-dependent ubiquitination and subsequent proteasomal degradation. Mechanistically, our data support a model in which CHK2 and CK1 initiate TAp63 phosphorylation, while HIPK2 and IKK{beta} act in a complementary manner to maintain protein stability during genotoxic stress. Disruption of HIPK2 or IKK{beta} activity reduces TAp63 stability, whereas their inhibition in vivo attenuates oocyte loss following DNA damage, resulting in increased preservation of the follicle pool. Importantly, these effects are observed across multiple systems, including mouse models and ex vivo goat ovary cultures, supporting an evolutionarily conserved role for this regulatory axis. Together, our findings uncover a previously unidentified layer of TAp63 regulation, in which phosphorylation not only contributes to its activation but also enhances protein stability, thereby fine-tuning oocyte responses to DNA damage. Our results further indicate that HIPK2 and IKK{beta}-mediated phosphorylation modulates oocyte survival under genotoxic stress, highlighting this pathway as a potential target for strategies aimed at limiting oocyte loss.

cell biology↗