Trichomonas vaginalis is an extracellular flagellated protozoan responsible for trichomoniasis, one of the most prevalent nonviral sexually transmitted infections. To persist in its host, T. vaginalis employs sophisticated gene regulation mechanisms to adapt to hostile environmental conditions. Although transcriptional regulation is crucial for this adaptation, the underlying molecular mechanisms remain poorly understood. Epigenetic regulation, particularly histone modifications, has emerged as a key modulator of gene expression. A previous study demonstrated that histone modifications, H3K4me3 and H3K27ac, promote active transcription. However, the complete extent of epigenetic regulation in T. vaginalis remains unclear. The present study extended these findings by exploring the repressive role of two additional histone H3 modifications, H3K9me3 and H3K27me3. Genome-wide analysis revealed that these modifications negatively correlated with gene expression, affecting protein-coding and transposable element genes (TEGs). These findings offer new insights into the dual role of histone modifications in activating and repressing gene expression and provide a more comprehensive understanding of epigenetic regulation in T. vaginalis. This expanded knowledge may inform the development of novel therapeutic strategies targeting the epigenetic machinery of T. vaginalis. [BMB Reports 2025
58(2): 82-88].