Linker Histone HIS-24 (H1.1) Cytoplasmic Retention Promotes Germ Line Development and Influences Histone H3 Methylation in Caenorhabditis elegans

Abstract

RNA interference with one of the eight Caenorhabditis elegans linker histone genes triggers desilencing of a repetitive transgene and developmental defects in the hermaphrodite germ line. These characteristics are similar to the phenotype of the C. elegans Polycomb group genes mes-2, mes-3, mes-4, and mes-6 (M. A. Jedrusik and E. Schulze, Development 128:1069-1080, 2001; I. Korf, Y. Fan, and S. Strome, Development 125:2469-2478, 1998). These Polycomb group proteins contribute to germ line-specific chromatin modifications. Using a his-24 deletion mutant and an isoform-specific antibody, we characterized the role of his-24 in C. elegans germ line development. We describe an unexpected cytoplasmic retention of HIS-24 in peculiar granular structures. This phenomenon is confined to the developing germ lines of both sexes. It is strictly dependent on the activities of the chromatinmodifying genes mes-2, mes-3, mes-4, and mes-6, as well as on the C. elegans sirtuin gene sir-2.1. A temperature shift experiment with a mes-3(ts) mutant revealed that mes gene activity is required in a time window ranging from L3 to the early L4 stage before the onset of meiosis. We find that the his-24(ok1024) mutant germ line is characterized by an increased level of the activating H3K4 methylation mark concomitant with a decrease of the repressive H3K9 methylation. In the germ line of his-24(ok1024) mes-3(bn35) double mutant animals, the repressive H3K27 methylation is more reduced than in the respective mes single mutant. These observations distinguish his-24 as an unusual element in the developmental regulation of germ line chromatin structure in C. elegans.Linker histones are highly abundant chromatin proteins that bind to the elementary structural unit of the chromatin, the nucleosome. Our previous work (9) characterized the Caenorhabditis elegans linker histone variant gene his-24 (H1.1) as a gene involved in the control of hermaphrodite germ line development. Using RNA interference (RNAi), desilencing of a repetitive transgene in the germ lines of both sexes had been shown. Additionally a low-penetrant cytological gonad phenotype occurred, where the germ line substantially lacked proliferation and differentiation. This cytological phenotype was observed in hermaphrodites but not in males. The combination of both observations related his-24 to the phenotype of the C. elegans Polycomb group genes, mes-2, mes-3, mes-4, and mes-6 (18; for reviews, see references 25 and 27). The precise gonadal expression pattern of HIS-24, its general mode of action, and its specific functional relationship to the mes genes remained unclear. No germ line phenotype of a linker histone mutant has been reported for mammals so far, although the mouse linker histone complement has recently been recognized as essential for embryogenesis (6). The present view on linker histones in general describes them as highly dynamic chromatin components. They are considered to be dispensable in single-cell eukaryotes (4, 16).The C. elegans SET domain histone methyl trans...

Novel Roles of Caenorhabditis elegans Heterochromatin Protein HP1 and Linker Histone in the Regulation of Innate Immune Gene Expression

“…Wild-type worms and his-24(ok1024) mutant worms were fixed with 1.85% paraformaldehyde and stained as previously described (26). The dissected gonads and worms were stained with the specific antibody raised against HIS-24K14me1 diluted 1:500 or 1:100.…”

“…C. elegans lysates were prepared and analyzed by Western blotting as previously described (26,27). For dot blots synthetic HIS-24 peptides monomethylated at K14 (residues 2 to 22) or unmethylated (residues 2 to 22) were used.…”

Less is more: specification of the germline by transcriptional repression

“…When the last germline blastomere P 4 divides into the PGCs Z2 and Z3, PIE-1 is degraded, the histone linker H1.1 (his-24) and the 'active' chromatin modifications H3meK4 and H4acK8 disappear, and Z2 and Z3 take on a unique condensed chromatin appearance (Jedrusik and Schulze, 2007;Schaner et al, 2003) (H. Furuhashi and W. Kelly, personal communication). During these events, Z2 and Z3 become transiently positive for pSer2, probably owing to the abrupt loss of PIE-1, but by mid-embryogenesis, pSer2 is once again strikingly reduced (H. Furuhashi and W. Kelly, personal communication).…”

The sirtuin SIRT6 regulates stress granules formation in C. elegans and in mammals

“…Worms from wild-type strain were fixed in 1% PFA (for staining using anti PGL-1/-3) or with methanol and acetone (for anti-GLH-1.2 staining) and stained, as previously described (Jedrusik and Schulze, 2007).…”