<p>Estrogen receptors (ESR1 and ESR2) play crucial roles in various processes during spermatogenesis. To elucidate individual roles of ESRs in male fertility, we developed <i>in vivo</i> selective ESR agonist administration models. Adult male rats treated with ESR1 and ESR2 agonist for 60 days show spermatogenic defects leading to reduced sperm counts and fertility. While studying epigenetic changes in the male germ line that could have affected fertility, we earlier observed a decrease in DNA methylation and its machinery upon ESR2 agonist treatment. Here, we explored the effects on histone modifications, which could contribute to decreased male fertility upon ESR agonist administration. ESR1 agonist treatment affected testicular levels of histone modifications associated with active and repressed chromatin states, along with heterochromatin marks. This was concomitant with deregulation of corresponding histone modifying enzymes in the testis. In addition, there was increased retention of histones along with protamine deficiency in the caudal spermatozoa after ESR1 agonist treatment. This could be due to the observed decrease in several chromatin remodeling proteins implicated in mediating histone-to-protamine exchange during spermiogenesis. The activating and repressing histone marks in spermatozoa, which play a critical role in early embryo development, were deregulated after both the ESR agonist treatments. Together, these epigenetic defects in the male germ line could affect the spermatozoa quality and lead to the observed decrease in fertility. Our results thus highlight the importance of ESRs in regulating different epigenetic processes during spermatogenesis, which are crucial for male fertility.</p
