Maternal TRIM28 safeguards bovine embryonic genome activation by regulating SAM-dependent methylation via lipid...

Does maternal TRIM28 coordinate lipid metabolism and epigenetic regulation during bovine preimplantation development?

Maternal TRIM28 preserves phospholipid homeostasis and S-adenosylmethionine (SAM) availability to maintain H3K9me3-dependent transcriptional repression during embryonic genome activation (EGA).

Successful preimplantation development requires tight coordination between metabolic remodeling and epigenetic reprogramming. TRIM28 is a conserved transcriptional co-repressor essential for chromatin silencing and embryonic development, but whether it integrates metabolic and epigenetic regulation during mammalian EGA remains unclear. Bovine embryos share several developmental features with human embryos, including the timing of major EGA and aspects of metabolic and epigenetic remodeling, making them a useful comparative model for investigating preimplantation development.

A mechanistic study was performed using bovine embryos generated by IVF after siRNA-mediated TRIM28 knockdown (KD) in oocytes. Embryonic development, transcriptional activity, lipid metabolism, SAM homeostasis, and epigenetic remodeling were evaluated across at least three independent biological replicates using RNA sequencing, lipidomics, immunofluorescence, ELISA assays, and metabolic rescue experiments.

TRIM28 KD embryos were generated by microinjection of siRNAs into bovine oocytes prior to IVF. Embryonic development was evaluated through the blastocyst stage. RNA sequencing, lipidomic profiling, ATP measurement, immunofluorescence staining, and ELISA assays were used to assess transcriptional regulation, lipid metabolism, SAM availability, and epigenetic modifications. Choline and betaine supplementation experiments were performed to evaluate rescue of developmental and epigenetic defects.

TRIM28 KD embryos showed impaired developmental progression around the 8-cell-to-morula transition, coinciding with major bovine EGA, and exhibited significantly reduced blastocyst formation. KD embryos exhibited widespread transcriptional dysregulation, increased global RNA synthesis, DNA damage, apoptosis, and ATP depletion. Lipidomic analyses revealed marked accumulation of triacylglycerols together with depletion of phosphatidylethanolamine (PE) and phosphatidylcholine (PC), indicating disrupted phospholipid homeostasis. TRIM28-deficient embryos also showed reduced H3K9me3 and DNA methylation levels accompanied by aberrant activation of EGA-associated genes. Mechanistically, altered phospholipid metabolism was associated with reduced intracellular SAM levels, raising the possibility that phospholipid remodeling affects the allocation of methyl donors between metabolic and chromatin methylation pathways. Importantly, supplementation with choline or betaine partially restored SAM levels, rescued H3K9me3 and DNA methylation defects, reduced DNA damage, and improved embryonic developmental competence.

The RNA-seq data generated in this study have been deposited in the Gene Expression Omnibus (GEO) database under accession number GSE330503.

The study was performed exclusively in an in vitro bovine embryo system. Therefore, the TRIM28-dependent mechanism described here should be considered experimentally established only in bovine embryos. Further studies using human stem cell-based embryo models or other ethically appropriate human experimental systems will be required to determine whether this pathway is conserved in human development.

These findings suggest that TRIM28 may contribute to the coordination of lipid metabolism, SAM availability, and epigenetic repression during bovine preimplantation development. The study also supports a possible link between methyl-donor availability and transcriptional regulation during the major EGA period. Given selected developmental similarities between bovine and human embryos, this mechanism warrants further investigation in human embryo-compatible experimental models.

This research was supported by National Key R&D Program of China (2021YFD1200400), National Natural Science Foundation of China (NSFC) (32472913), China Agriculture Research System of MOF and MARA (CARS-37).

The authors declare no competing interests.