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Di- and trimethylation of histone H4 lysine20 (H4K20) are thought to play an important role in controlling gene expression in vertebrates and in Drosophila. By inducing a null mutation in Drosophiht Suv4-20, we show that it encodes the histone H4 lysine20 di- and trimethyltransferase. In Suv4-20 mutants, the H4K20 di- and trimethyl marks are strongly reduced or absent, and the monomethyl mark is significantly increased. We find that even with this biochemical function, Suv4-20 is not required tot survival wad does not control position-effect variegation (PEV).

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.12.019 Byline: Dmitry Karachentsev, Marina Druzhinina, Ruth Steward Keywords: Histone methylation; Chromatin; Free histones; Cell cycle and mitosis; Drosophila Abstract: Methylation of specific amino acids in histone tails is responsible for packaging DNA into condensed, repressed chromatin, and into open chromatin that is accessible to the transcription machinery. Monomethylation and trimethylation of histone H4-lysine 20 (H4-K20) control the formation of repressed chromatin. Using antibodies that specifically recognize the three methyl marks of histone H4-K20, we characterized their regulation during the cell cycle and throughout development. We find free mono- and trimethylated histone H4-K20 in unfertilized Drosophila eggs and in S2 tissue culture cells. Soluble mono-. di-, and trimethylated H4-K20 are also found in HeLa cells. These soluble modified histones may represent a pool of free histones that can rapidly be incorporated into chromatin. The three methyl marks are each regulated differentially during development and their detection on western blots does not overlap with their detection on chromosomes. Monomethylated H4-K20 is detected on condensed chromosomes throughout development, while di- and trimethylated H4-K20 are detected on metaphase chromosomes at specific stages. Our results suggest that the detection of methylated H4-K20 on chromosomes may reveal chromatin packaging rather than the distribution of the methyl marks. Author Affiliation: Waksman Institute, Department of Molecular Biology and Biochemistry, Cancer Institute of New Jersey, Rutgers University, 190 Frelinghuysen Road, Piscataway, NJ 08854, USA Article History: Received 22 June 2006; Revised 23 November 2006; Accepted 8 December 2006

Abstract Background Transport of macromolecules into and out of the nucleus is a highly regulated process. The RanGTP/RanGDP gradient controls the trafficking of molecules exceeding the diffusion limit of the nuclear pore across the nuclear envelope. Results We found genetic interaction between genes establishing the Ran gradient, nuclear transport factor 2 (ntf-2), Ran GTPase activating protein (Sd), and the gene encoding Drosophila Profilin, chickadee (chic). The severe eye phenotype caused by reduction of NTF2 is suppressed by loss of function mutations in chic and gain of function mutations in Sd (RanGAP). We show that in chic mutants, as in Sd-RanGAP, nuclear export is impaired. Conclusion Our data suggest that Profilin and the organization of the actin cytoskeleton play an important role in nuclear trafficking.

We have identified a new gene, Zfrp8, as being essential for hematopoiesis in Drosophila, Zfrp8 (Zinc finger protein RP-8) is the Drosophila ortholog of the PDCD2 (programmed cell death 2) protein of unknown function, and is highly conserved in all eukaryotes. Zfrp8 mutants present a developmental delay, lethality during larval and pupal stages and hyperplasia of the hematopoietic organ, the lymph gland. This overgrowth results from an increase in proliferation of undifferentiated hemocytes throughout development and is accompanied by abnormal differentiation of hemocytes. Furthermore, the subcellular distribution of γ-Tubulin and Cyclin B is affected. Consistent with this, the phenotype of the lymph gland of Zfpr8 heterozygous mutants is dominantly enhanced by the l(1)dd4 gene encoding Dgrip91, which is involved in anchoring γ-Tubulin to the centrosome. The overgrowth phenotype is also enhanced by a mutation in Cdc27, which encodes a component of the anaphase-promoting complex (APC) that regulates the degradation of cyclins. No evidence for an apoptotic function of Zfrp8 was found. Based on the phenotype, genetic interactions and subcellular localization of Zfrp8, we propose that the protein is involved in the regulation of cell proliferation from embryonic stages onward, through the function of the centrosome, and regulates the level and localization of cell-cycle components. The overproliferation of cells in the lymph gland results in abnormal hemocyte differentiation. [ABSTRACT FROM AUTHOR]

Abstract: Despite undergoing normal development and acquiring normal morphology and motility, mutations in spe-38 or trp-3/spe-41 cause identical phenotypes in Caenorhabditis elegans—mutant sperm fail to fertilize oocytes despite direct contact. SPE-38 is a novel, four-pass transmembrane protein and TRP-3/SPE-41 is a Ca2+-permeable channel. Localization of both of these proteins is confined to the membranous organelles (MOs) in undifferentiated spermatids. In mature spermatozoa, SPE-38 is localized to the pseudopod and TRP-3/SPE-41 is localized to the whole plasma membrane. Here we show that the dynamic redistribution of TRP-3/SPE-41 from MOs to the plasma membrane is dependent on SPE-38. In spe-38 mutant spermatozoa, TRP-3/SPE-41 is trapped within the MOs and fails to reach the cell surface despite MO fusion with the plasma membrane. Split-ubiquitin yeast-two-hybrid analyses revealed that the cell surface localization of TRP-3/SPE-41 is likely regulated by SPE-38 through a direct protein–protein interaction mechanism. We have identified sequences that influence the physical interaction between SPE-38 and TRP-3/SPE-41, and show that these sequences in SPE-38 are required for fertility in transgenic animals. Despite the mislocalization of TRP-3/SPE-41 in spe-38 mutant spermatozoa, ionomycin or thapsigargin induced influx of Ca2+ remains unperturbed. This work reveals a new paradigm for the regulated surface localization of a Ca2+-permeable channel. [Copyright &y& Elsevier]