Phosphorylation of histone H4 Ser1 regulates sporulation in yeast and is conserved in fly and mouse spermatogenesis

Abstract

Sporulation in Saccharomyces cerevisiae is a highly regulated process wherein a diploid cell gives rise to four haploid gametes. In this study we show that histone H4 Ser1 is phosphorylated (H4 S1ph) during sporulation, starting from mid-sporulation and persisting to germination, and is temporally distinct from earlier meiosis-linked H3 S10ph involved in chromosome condensation. A histone H4 S1A substitution mutant forms aberrant spores and has reduced sporulation efficiency. Deletion of sporulation-specific yeast Sps1, a member of the Ste20 family of kinases, nearly abolishes the sporulation-associated H4 S1ph modification. H4 S1ph may promote chromatin compaction, since deletion of SPS1 increases accessibility to antibody immunoprecipitation; furthermore, either deletion of Sps1 or an H4 S1A substitution results in increased DNA volume in nuclei within spores. We find H4 S1ph present during Drosophila melanogaster and mouse spermatogenesis, and similar to yeast, this modification extends late into sperm differentiation relative to H3 S10ph. Thus, H4 S1ph may be an evolutionarily ancient histone modification to mark the genome for gamete-associated packaging.[Keywords: Saccharomyces cerevisiae; fly and mouse spermatogenesis; genome compaction; histone H4 phosphorylation; kinase; yeast sporulation] Genetic and epigenetic information is transferred to a new cell generation through the gametogenesis process. Dramatic changes in chromatin structure occur during both metazoan spermatogenesis and yeast sporulation involving DNA compaction. In addition, spermatogenesis requires removal of most canonical histones and substitution with histone variants and histone replacement proteins (Govin et al. 2004; Kimmins and SassoneCorsi 2005).The nucleosome is the fundamental repeating unit of chromatin and harbors an octamer of basic histone proteins (two copies of dimeric H3/H4 and H2A/H2B) wrapped by ∼147 base pairs (bp) of DNA (Luger et al. 1997). Nucleosomes pack into higher-order chromatin structures, whose precise architectures are not understood. Post-translational modifications (PTMs) of histones (including acetylation, phosphorylation, methylation, and ubiquitylation) regulate chromatin function and contribute to its folding. PTMs occur in distinct patterns and in diverse cellular pathways. For example, H3 S10ph correlates with both mitotic/meiotic chromosome condensation and transcriptional activation (Nowak and Corces 2004). Chromosome condensation includes a large number of possibly redundant histone phosphorylation marks, including S10 (Hendzel et al. 1997), T3 (Polioudaki et al. 2004), T11 (Preuss et al. 2003, S28 (Goto et al. 1999S28 (Goto et al. , 2002 within H3, S1 within H4 (Barber et al. 2004), S1 within H2A (Barber et al. 2004), and S10 in H2B (Ahn et al. 2005b). Phosphorylation at H3 S10 has been causally linked to mitotic

Packing for the germy: the role of histone H4 Ser1 phosphorylation in chromatin compaction and germ cell development: Figure 1.

“…The products of these genes are involved in the control or mechanics of meiotic division, including chromatin compaction. Genes encoding two Ser/Thr protein kinases, Smk1 and Sps1, are among these middle sporulation genes, and Krishnamoorthy et al (2006) wondered whether these protein kinases are required for H4 S1 phosphorylation. They elegantly demonstrated SPS1 but not SMK1 is required for phosphorylation of H4 S1during sporulation.…”

“…It is significant that this histone modification is evolutionarily conserved, from Drosophila to mammals. H4 S1 is phosphorylated during sporulation, and unlike H3 S10ph, appears to be a stable modification Krishnamoorthy et al (2006) report a strong increase in H4 S1ph abundance 8-12 h into the sporulation program. However, the phosphorylation pattern for H3 S10 and H4 S1 appears to be temporally distinct during sporulation: Within 4 h of starvation, H3 S10 phosphorylation peaks during the early stage of sporulation and then declines; H4 S1ph appears nearing the completion of meiosis I and II and persists thereafter.…”

“…In this issue of Genes and Development, Krishnamoorthy et al (2006) have elegantly demonstrated that a conserved histone modification, phosphorylation of Ser1 on histone 4 (H4 S1ph) is involved in chromatin compaction during sporulation in yeast, and that it is an evolutionarily conserved mark found during Drosophila melanogaster and mouse germ cell development.…”

“…In this issue of Genes and Development, Krishnamoorthy et al (2006) re-examined the function of the previously described phosphorylation of S1 of histone H4 in chromatin compaction during sporulation. They found H4Ser1ph to be required for proper chromatin compaction during sporulation, and also for gametogenesis.…”

“…Therefore, Krishnamoorthy et al (2006) sought to determine whether an H4 S1A mutation demonstrates defects in sporulation. Diploid cells possessing a substitution of alanine for Ser1 have defects in sporulation.…”