Epigenetic mechanisms profoundly regulate gene expression, developmental trajectories, and phenotypic variation, extending biological influence beyond DNA sequence alone. A growing body of evidence suggests that environmental exposures, including pollutants, drugs, stress, and diet, can induce germline and early embryonic epimutations that alter developmental programs with lasting consequences for neurodevelopmental and cognitive outcomes. However, the fields most relevant to these processes have largely developed independently. These include germline epigenetics, early embryonic patterning, neurodevelopment and cognitive regulation, and intergenerational or transgenerational inheritance. Each field has its own conceptual frameworks and mechanistic models. This fragmentation obscures the biological reality that these systems are tightly interconnected: environmentally induced epigenetic perturbations in gametes can reshape the epigenetic landscape of the early embryo, influence lineage allocation during gastrulation, and ultimately modify the molecular architecture of the developing central nervous system. A systems–biology perspective capable of linking germline epimutations and early embryonic epigenetic instability to later neurodevelopmental and cognitive phenotypes and their potential inheritance is therefore required. This review synthesizes current evidence across these traditionally isolated domains and proposes a coherent mechanistic framework linking germ cell epimutations and early embryonic epigenetic instability to the emergence of neurodevelopmental and cognitive phenotypes. By bridging these conceptual gaps, we aim to establish a cohesive foundation for understanding how early epigenetic disruptions generate long-lasting and in some cases heritable effects on brain development and cognitive function.

Background/Objectives: Parental environmental factors can shape developmental outcomes through epigenetic mechanisms that regulate gene expression. While maternal dietary effects on offspring epigenetics have been well characterized, the impact of paternal diet on embryonic DNA methylation remains poorly understood. Here, we investigated the effect of paternal methionine supplementation on DNA methylation patterns in preimplantation embryos in Polypay sheep. Methods: Four yearling rams (two control and two methionine-supplemented) were bred to twelve ewes following estrus synchronization and superovulation. Embryos were collected after natural mating and analyzed using whole-genome bisulfite sequencing (WGBS). Results: A total of 842 differentially methylated cytosines (DMCs) were identified in embryos derived from methionine-supplemented sires compared to controls, with 835 hypermethylated and 7 hypomethylated. The majority of DMCs were located in intergenic regions, with minimal representation in exonic regions. To assess overlap between parental dietary effects, DMCs identified in this study were compared with those previously reported in embryos derived from methionine-supplemented dams. Eight hypermethylated DMCs were shared between the two datasets, while no hypomethylated DMCs overlapped. To evaluate the functional relevance of differentially methylated genes, we performed siRNA-mediated knockdown of SSU72, a gene associated with multiple DMCs. Knockdown of SSU72 resulted in an average 18% decrease in blastocyst formation rate (p < 0.001). Conclusions: These results demonstrate that paternal methionine supplementation alters embryonic DNA methylation patterns and that affected genes may play critical roles in early embryonic development, contributing to fetal programming.

Evolutionary success in mammals requires coordinated regulation of cognitive functions and reproductive capacity. Such coordination must involve shared genes and molecular pathways between the brain and germ cells, yet direct evidence linking cognition to reproduction across species remains limited. Here, proteomic and transcriptomic analyses were performed experimentally in Ovis aries and Rattus norvegicus, while transcriptomic datasets from Mus musculus, Macaca mulatta, and Homo sapiens were analyzed in silico. We identified 8,464 protein-coding genes shared between the brain and sperm/testis and conserved across five species. In rats, 8,444 of these genes were also shared between the brain and the ovary. Functional annotation classified 3,890 genes as associated with both neurological and reproductive functions, and 1,752 as uncharacterized in these contexts, highlighting candidates for future studies on reproductive and neurological disorders. These findings reveal a deeply conserved genetic network linking neurological and reproductive systems, underscoring the evolutionary interplay that supports mammalian fitness.