Dynamic Regulation of Histone H3 Methylation at Lysine 4 in Mammalian Spermatogenesis1

Abstract

Spermatogenesis is a highly complex cell differentiation process that is governed by unique transcriptional regulation and massive chromatin alterations, which are required for meiosis and postmeiotic maturation. The underlying mechanisms involve alterations to the epigenetic layer, including histone modifications and incorporation of testis-specific nuclear proteins, such as histone variants and protamines. Histones can undergo methylation, acetylation, and phosphorylation among other modifications at their N-terminus, and these modifications can signal changes in chromatin structure. We have identified the temporal and spatial distributions of histone H3 mono-, di-, and trimethylation at lysine 4 (K4), and the lysine-specific histone demethylase AOF2 (amine oxidase flavin-containing domain 2, previously known as LSD1) during mammalian spermatogenesis. Our results reveal tightly regulated distributions of H3-K4 methylation and AOF2, and that H3-K4 methylation is very similar between the mouse and the marmoset. The AOF2 protein levels were found to be higher in the testes than in the somatic tissues. The distribution of AOF2 matched the cell- and stage-specific patterns of H3-K4 methylation. Interaction studies revealed unique epigenetic regulatory complexes associated with H3-K4 methylation in the testis, including the association of AOF2 and methyl-CpG-binding domain protein 2 (MBD2a/b) in a complex with histone deacetylase 1 (HDAC1). These studies enhance our understanding of epigenetic modifications and their roles in chromatin organization during male germ cell differentiation in both normal and pathologic states.

Mechanisms involved in the regulation of histone lysine demethylases

“…For instance, studies in organisms ranging from fission yeast to mice support a role for the H3K4me2/1 demethylase KDM1 (LSD1) in meiosis. The mammalian KDM1/LSD1 shows relatively higher levels of expression in mouse testis and related tissues, complementing the observed lower levels of H3K4me2 in these tissues [4]. Mutations of the fly KDM1 homolog lead to sex-specific embryonic lethality and sterility in the surviving (primarily female) offspring, likely due to defects in ovary development [5].…”

SirT1 is required in the male germ cell for differentiation and fecundity in mice

“…This process involves the removal of most histones from chromatin and the eventual deposition of protamines -highly charged proteins that facilitate and maintain the condensation of the sperm DNA (Balhorn, 1982). The initiation of this process is associated with hyper-acetylation of histones, H2A and H2B monoubiquitination, as well as H3 K4 trimethylation (Baarends et al, 1999;Godmann et al, 2007;Hazzouri et al, 2000). To examine whether total histone acetylation is altered in the KO animals, we examined acid-extracted proteins from the chromatin of germ cell fractions.…”

Histone H3.3 regulates dynamic chromatin states during spermatogenesis

“…During spermatogenesis, a complex interplay of histone posttranslational modifications (PTMs) take place in the nuclei of immature germ cells as they develop into mature spermatozoon (Chen et al, 1998;Godmann et al, 2007;Lewis et al, 2003;Payne and Braun, 2006;Rathke et al, 2013;Tachibana et al, 2007;van der Heijden et al, 2006;Zheng et al, 2008). Together with such histone PTMs, histone variants play a major role in the protamine transition and chromatin reorganization process during spermatogenesis, and many histone variants of histone H1 (H1t, H1T2 HILS1), H2A and H2B (TH2A, TH2B, ssH2B, H2A.B.bd, H2BL1, H2BL2, H2AL1-H2AL3) and H3 (H3t, H3.3) become expressed in specific germ cell types or are testes-specific (Lewis et al, 2003;Rathke et al, 2013).…”