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 chromatin-modifying 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.

We thank Sabine Pitzel and Angelika Schäfer for their excellent technical assistance, Bettina Schulze and Krzysztof Drabikowski for critically reading the manuscript, and Ralf Baumeister (Freiburg, Germany) and Ernst Wimmer (Göttingen, Germany) for their support of this work in their respective labs. We gratefully received the excellent anti-H3K27me3 antibody from T. Jenuwein (Vienna, Austria) and the LET-858::GFP reporter strain PD7271 from W. G. Kelly (Atlanta, GA).

Some C. elegans strains used were obtained from the Caenorhabditis Genetics Center (CGC), which is funded by the NIH National Center for Research Resources (NCRR). The his-24(ok1024) deletion mutant was provided by the C. elegans Gene Knockout Consortium, which is publicly funded. This work was supported by German National Funding Agency (DFG) grants SCHU 1033/3-4 to E. Schulze and JE 505/1-1 to M. Jedrusik.