Lysine methylation of histones is recognized as an important component of an epigenetic indexing system demarcating transcriptionally active and inactive chromatin domains. Trimethylation of histone H3 lysine 4 (H3K4me3) marks transcription start sites of virtually all active genes. Recently, we reported that the WD40-repeat protein WDR5 is important for global levels of H3K4me3 and control of HOX gene expression. Here we show that a plant homeodomain (PHD) finger of nucleosome remodelling factor (NURF), an ISWI-containing ATP-dependent chromatin-remodelling complex, mediates a direct preferential association with H3K4me3 tails. Depletion of H3K4me3 causes partial release of the NURF subunit, BPTF (bromodomain and PHD finger transcription factor), from chromatin and defective recruitment of the associated ATPase, SNF2L (also known as ISWI and SMARCA1), to the HOXC8 promoter. Loss of BPTF in Xenopus embryos mimics WDR5 loss-of-function phenotypes, and compromises spatial control of Hox gene expression. These results strongly suggest that WDR5 and NURF function in a common biological pathway in vivo, and that NURF-mediated ATP-dependent chromatin remodelling is directly coupled to H3K4 trimethylation to maintain Hox gene expression patterns during development. We also identify a previously unknown function for the PHD finger as a highly specialized methyl-lysine-binding domain.

Selenium has been implicated in cancer prevention, but the mechanism and possible involvement of selenoproteins in this process are not understood. To elucidate whether the 15-kDa selenoprotein may play a role in cancer etiology, the complete sequence of the human 15-kDa protein gene was determined, and various characteristics associated with expression of the protein were examined in normal and malignant cells and tissues. The 51-kilobase pair gene for the 15-kDa selenoprotein consisted of five exons and four introns and was localized on chromosome 1p31, a genetic locus commonly mutated or deleted in human cancers. Two stemloop structures resembling selenocysteine insertion sequence elements were identified in the 3-untranslated region of the gene, and only one of these was functional. Two alleles in the human 15-kDa protein gene were identified that differed by two single nucleotide polymorphic sites that occurred within the selenocysteine insertion sequence-like structures. These 3-untranslated region polymorphisms resulted in changes in selenocysteine incorporation into protein and responded differently to selenium supplementation. Human and mouse 15-kDa selenoprotein genes manifested the highest level of expression in prostate, liver, kidney, testis, and brain, and the level of the selenoprotein was reduced substantially in a malignant prostate cell line and in hepatocarcinoma. The expression pattern of the 15-kDa protein in normal and malignant tissues, the occurrence of polymorphisms associated with protein expression, the role of selenium in differential regulation of polymorphisms, and the chromosomal location of the gene may be relevant to a role of this protein in cancer.The essential trace element selenium occurs in several proteins found in bacteria (1), archaea (2), and eukaryotes (1, 3). All of the known selenoproteins described to date incorporate selenium into protein co-translationally as the amino acid selenocysteine (Sec) 1 in response to the UGA codon (1, 3, 4), with the exception of several bacterial molybdenum-containing enzymes such as Clostridium barkeri nicotinic acid hydroxylase that contains an active center dissociable selenium species (5-7). Among the selenoproteins thus far identified in mammals are four glutathione peroxidases, three thioredoxin reductases, three thyroid hormone deiodinases, selenophosphate synthetase, selenoprotein P, selenoprotein W, selenoprotein T, selenoprotein R (also called selenoprotein X), selenoprotein N, and a 15-kDa selenoprotein (1, 3, 8 -10).The 15-kDa selenoprotein was initially identified as a strongly labeled protein that was detected when human T cells were grown in the presence of [75 Se]selenite (11). The open reading frame within the human 15-kDa protein cDNA coded for 162 residues and contained an in-frame TGA codon that would result in the incorporation of Sec at codon position 93. A putative stem-loop structure, designated the Sec insertion sequence (SECIS) element, was predicted in the 3Ј-untranslated region (3Ј-UTR). SECIS elements are ...

Drosophila NURF is an ISWI-containing ATP-dependent chromatin remodeling complex that regulates transcription by catalyzing nucleosome sliding. To determine in vivo gene targets of NURF, we performed whole genome expression analysis on mutants lacking the NURF-specific subunit NURF301. Strikingly, a large set of ecdysone-responsive targets is included among several hundred NURF-regulated genes. Null Nurf301 mutants do not undergo larval to pupal metamorphosis, and also enhance dominant-negative mutations in ecdysone receptor. Moreover, purified NURF binds EcR in an ecdysone-dependent manner, suggesting it is a direct effector of nuclear receptor activity. The conservation of NURF in mammals has broad implications for steroid signaling.Supplemental material is available at http://www.genesdev.org.

The Drosophila nucleosome remodeling factor (NURF) is an ISWI-containing chromatin remodeling complex that catalyzes ATP-dependent nucleosome sliding. By sliding nucleosomes, NURF has the ability to alter chromatin structure and regulate transcription. Previous studies have shown that mutation of Drosophila NURF induces melanotic tumors, implicating NURF in innate immune function. Here, we show that NURF mutants exhibit identical innate immune responses to gain-of-function mutants in the Drosophila JAK/STAT pathway. Using microarrays, we identify a common set of target genes that are activated in both mutants. In silico analysis of promoter sequences of these defines a consensus regulatory element comprising a STAT-binding sequence overlapped by a binding-site for the transcriptional repressor Ken. NURF interacts physically and genetically with Ken. Chromatin immunoprecipitation (ChIP) localizes NURF to Ken-binding sites in hemocytes, suggesting that Ken recruits NURF to repress STAT responders. Loss of NURF leads to precocious activation of STAT target genes.

Leukocyte-like cells called hemocytes have key functions in Drosophila innate immunity. Three hemocyte types occur: plasmatocytes, crystal cells, and lamellocytes. In the absence of qimmune challenge, plasmatocytes are the predominant hemocyte type detected, while crystal cells and lamellocytes are rare. However, upon infestation by parasitic wasps, or in melanotic mutant strains, large numbers of lamellocytes differentiate and encapsulate material recognized as “non-self”. Current models speculate that lamellocytes, plasmatocytes and crystal cells are distinct lineages that arise from a common prohemocyte progenitor. We show here that over-expression of the CoREST-interacting transcription factor Chn in plasmatocytes induces lamellocyte differentiation, both in circulation and in lymph glands. Lamellocyte increases are accompanied by the extinction of plasmatocyte markers suggesting that plasmatocytes are transformed into lamellocytes. Consistent with this, timed induction of Chn over-expression induces rapid lamellocyte differentiation within 18 hours. We detect double-positive intermediates between plasmatocytes and lamellocytes, and show that isolated plasmatocytes can be triggered to differentiate into lamellocytes in vitro, either in response to Chn over-expression, or following activation of the JAK/STAT pathway. Finally, we have marked plasmatocytes and show by lineage tracing that these differentiate into lamellocytes in response to the Drosophila parasite model Leptopilina boulardi. Taken together, our data suggest that lamellocytes arise from plasmatocytes and that plasmatocytes may be inherently plastic, possessing the ability to differentiate further into lamellocytes upon appropriate challenge.