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Histone methylation is a key epigenetic mechanism and plays a major role in regulating gene expression during oocyte maturation and early embryogenesis. This mechanism can be briefly defined as the process by which methyl groups are transferred to lysine and arginine residues of histone tails extending from nucleosomes. While methylation of the lysine residues is catalyzed by histone lysine methyltransferases (KMTs), protein arginine methyltransferases (PRMTs) add methyl groups to the arginine residues. When necessary, the added methyl groups can be reversibly removed by histone demethylases (HDMs) by a process called histone demethylation. The spatiotemporal regulation of methylation and demethylation in histones contributes to modulating the expression of genes required for proper oocyte maturation and early embryonic development. In this review, we comprehensively evaluate and discuss the functional importance of dynamic histone methylation in mammalian oocytes and early embryos, regulated by KMTs, PRMTs, and HDMs. [ABSTRACT FROM AUTHOR]

Histone methylation that regulates gene expression during spermatogenesis is the addition of methyl groups to lysine or arginine residues of histones by the action of histone methyltransferases. The histone methyltransferases SETD1B-CFP1, G9A, SETDB1, and SETD2 spatiotemporally establish the histone methylation marks, H3K4me3, H3K9me2, H3K9me3, and H3K36me3, respectively. Failures in forming these marks result in changed transcriptional activity and increased apoptosis in male germ cells, eventually in male infertility. The potential relationship between decreasing male fertility during paternal aging and the expression patterns of these histone methyltransferases and their target effects has not been evaluated in detail yet. Herein, we aimed to determine expression patterns of the SETD1B, CFP1, G9A, SETDB1, and SETD2 proteins, their methylation marks and target effects in the postnatal mouse testes. Five groups were created from Balb/C male mice as the following: early (1- and 2-week-old, n=5 from each one), prepubertal (3- and 4-week-old; n=4 from each one), pubertal (5- and 6-week-old, n=4 from each one), postpubertal (16-, 18-, and 20-week-old, n=4 from each one) and aged (48-, 50-, and 52-week-old, n=6, 5, and 6 from each one, respectively). The obtained testes were fixed by immersing in Bouin's solution at +4 oC overnight and then embedded in paraffin by using routine tissue procedures. With using immunohistochemistry, we stained β-galactosidase (as a senescence marker), the histone lysine methyltransferases, histone methylation marks and their target effects. The relative expressions were analyzed with the ImageJ software program and then evaluated using one-way ANOVA and post hoc Tukey test. The relative β-galactosidase levels gradually increased from early to aged groups (P <0.001). The SETD1B protein was mainly localized in the nuclei of the spermatogenic cells. Its expression and the target methylation H3K4me3 gradually enhanced from early to aged groups (P <0.01). In contrast, the CFP1 level decreased in the aged group compared with the early group (P <0.0001). While SETDB1 level increased from early to aged groups (P <0.05), H3K9me3 methylation showed an increase in the aged group compared to the prepubertal and pubertal groups (P <0.05). Another histone methyltransferase SETD2 had the highest expression in the aged group, as H3K36me3 did (P <0.0001). The G9A level enhanced significantly in the aged group (P <0.0001), while the target methylation mark H3K9me2 did not differ between groups. Interestingly, the transcriptional activation marker PS2 displayed no significant changes among the groups. The cleaved caspase 3 level decreased in the seminiferous tubules of pubertal, postpubertal, and aged groups (P <0.001). These findings suggest that the changed expression of the histone lysine methyltransferases and histone methylation marks in the postnatal mouse testes may contribute to decreasing spermatogenic activity during paternal aging. [ABSTRACT FROM AUTHOR]

DNA methylation plays crucial role in regulating gene expression. It involves adding methyl groups by DNA methyltransferases (DNMTs) to cytosine residues in CpG dinucleotides. DNMT3A is primarily responsible for establishing de novo DNA methylation. Basically, DNA methylation is implicated in various processes, including germ cell development, sex determination, and maintenance of spermatogenesis. DNA methylation patterns are dynamically regulated during these processes, and potential alterations can adversely affect gene expression and development. The global DNA methylation levels change with age during different stages of spermatogenesis, but its molecular details are not elucidated yet. In this study, we aimed to investigate DNA methylation dynamics in the postnatal mouse testes from early to aged periods by evaluating 5mC and DNMT3A relative levels and their localizations. Three groups were created from Balb/C male mice as following: pubertal (6-week-old, n=4), postpubertal (18-week-old; n=4), and aged (50-week-old, n=5). Obtained testes from these mice were fixed by immersing them in Bouin's solution at +4 oC overnight and then embedded in paraffin. After performing immunohistochemistry for the DNMT3A and 5mC on the paraffin sections, we analyzed their relative levels with the ImageJ software program. The data were analyzed using one-way ANOVA and post hoc Tukey test for determining statistical significance (P <0.05). In all groups, DNMT3A protein was mainly localized in the nuclei of the cells found in the seminiferous tubules. While positive immunoreactivity was detected in the nuclei of spermatogonial cells, there was no staining in the nuclei of spermatocytes, round spermatids, and Sertoli cells. Based on our analyses, there was no significant difference between the groups in the relative DNMT3A protein level. Similarly, 5mC staining was also detected in the nuclei of spermatogenic cells of seminiferous tubules. It is important to note that the relative expression of 5mC was higher in the aged group compared to the pubertal and postpubertal groups (P <0.05). Although we did not find a significant change in the DNMT3A expression among postnatal mouse testes, other DNMTs should also be analyzed in the same groups such as DNMT1 and DNMT3B, and DNA demethyltransferases (TET1, TET2, and TET3. The finding related to increasing global DNA methylation in the aged group is comparable to the increasing transcriptional activity during paternal aging. The potential relationship should be analyzed in more detailed studies on isolated spermatogenic cells from pubertal and aged mice. [ABSTRACT FROM AUTHOR]