Drosophila ISWI, a highly conserved member of the SWI2/SNF2 family of ATPases, is the catalytic subunit of three chromatin-remodeling complexes: NURF, CHRAC, and ACF. To clarify the biological functions of ISWI, we generated and characterized null and dominant-negative ISWI mutations. We found that ISWI mutations affect both cell viability and gene expression during Drosophila development. ISWI mutations also cause striking alterations in the structure of the male X chromosome. The ISWI protein does not colocalize with RNA Pol II on salivary gland polytene chromosomes, suggesting a possible role for ISWI in transcriptional repression. These findings reveal novel functions for the ISWI ATPase and underscore its importance in chromatin remodeling in vivo.

Polycomb group response elements (PREs) mediate the mitotic inheritance of gene expression programs and thus maintain determined cell fates. By default, PREs silence associated genes via the targeting of Polycomb group (PcG) complexes. Upon an activating signal, however, PREs recruit counteracting trithorax group (trxG) proteins, which in turn maintain target genes in a transcriptionally active state. Using a transgenic reporter system, we show that the switch from the silenced to the activated state of a PRE requires noncoding transcription. Continuous transcription through the PRE induced by an actin promoter prevents the establishment of PcG-mediated silencing. The maintenance of epigenetic activation requires transcription through the PRE to proceed at least until embryogenesis is completed. At the homeotic bithorax complex of Drosophila, intergenic PRE transcripts can be detected not only during embryogenesis, but also at late larval stages, suggesting that transcription through endogenous PREs is required continuously as an anti-silencing mechanism to prevent the access of repressive PcG complexes to the chromatin. Furthermore, all other PREs outside the homeotic complex we tested were found to be transcribed in the same tissue as the mRNA of the corresponding target gene, suggesting that anti-silencing by transcription is a fundamental aspect of the cellular memory system. Chromosomal elements termed PREs (Polycomb group response elements) mediate the mitotic inheritance of transcriptional programs, thus ensuring the stable propagation of cell fates throughout development. In the repressed state, PREs act as silencers by recruiting Polycomb group (PcG) complexes to chromatin. When in the activated mode, however, PREs are controlled by the counteracting trithorax group (trxG) proteins, which in turn promote the formation of a transcriptionally competent chromatin structure (for review, see . Besides the well studied homeotic genes in the Drosophila bithorax complex (BX-C), PREs have been shown to be associated with a number of target genes (Kassis 1994;Maurange and Paro 2002;Bloyer et al. 2003;Ringrose et al. 2003). However, despite extensive analyses of the dynamics of PcG and trxG protein association with a PRE and requirements during the establishment of either the silenced or the activated state (Orlando et al. 1998;Poux et al. 2001;Mohd-Sarip et al. 2002;Déjardin and Cavalli 2004), it is not known how the decision between the recruitment of either repressive PcG or activating trxG complexes to a PRE is taken.There is accumulating evidence that silencing represents the default state of these elements, whereas the conversion of a PRE into the active chromatin mode is triggered by the embryonic activation of the target gene promoter (Busturia and Bienz 1993;Chan et al. 1994;Paro 1998, 1999;Klymenko and Müller 2004;Sengupta et al. 2004). However, it is not clear how this transcriptional activity is communicated to a PRE and, as a consequence, which mechanism regulates the epigenetic switch of a PRE into t...

A set of circulating microRNAs (miR-125a-5p, miR-125b-5p, and miR-143-3p) associates with acute IS and might have clinical utility as an early diagnostic marker.

Old age is associated with a progressive decline of mitochondrial function and changes in nuclear chromatin. However, little is known about how metabolic activity and epigenetic modifications change as organisms reach their midlife. Here, we assessed how cellular metabolism and protein acetylation change during early aging in Drosophila melanogaster. Contrary to common assumptions, we find that flies increase oxygen consumption and become less sensitive to histone deacetylase inhibitors as they reach midlife. Further, midlife flies show changes in the metabolome, elevated acetyl-CoA levels, alterations in protein-notably histone-acetylation, as well as associated transcriptome changes. Based on these observations, we decreased the activity of the acetyl-CoA-synthesizing enzyme ATP citrate lyase (ATPCL) or the levels of the histone H4 K12-specific acetyltransferase Chameau. We find that these targeted interventions both alleviate the observed aging-associated changes and promote longevity. Our findings reveal a pathway that couples changes of intermediate metabolism during aging with the chromatin-mediated regulation of transcription and changes in the activity of associated enzymes that modulate organismal life span.

The proteins of the trithorax and Polycomb groups maintain the differential expression pattern of homeotic genes established by the early embryonic patterning system during development. These proteins generate stable and heritable chromatin structures by acting via particular chromosomal memory elements. We established a transgenic assay system showing that the Polycomb group response elements bxd and Mcp confer epigenetic inheritance throughout development. With previously published data for the Fab7 cellular memory module, we confirmed the cellular memory function of Polycomb group response elements. In Drosophila melanogaster, several of these memory elements are located in the large intergenic regulatory regions of the homeotic bithorax complex. Using a transgene assay, we showed that transcription through a memory element correlated with the relief of silencing imposed by the Polycomb group proteins and established an epigenetically heritable active chromatin mode. A memory element remodeled by the process of transcription was able to maintain active expression of a reporter gene throughout development. Thus, transcription appears to reset and change epigenetic marks at chromosomal memory elements regulated by the Polycomb and trithorax proteins. Interestingly, in the bithorax complex of D. melanogaster, the segment-specific expression of noncoding intergenic transcripts during embryogenesis seems to fulfill this switching role for memory elements regulating the homeotic genes.Developmental decisions resulting in differential gene expression patterns need to be maintained over many rounds of cell divisions. The proteins of the Polycomb group (PcG) and trithorax group (trxG) lock determined gene expression states by generating higher-order chromatin structures which are stable and heritable. The members of the PcG protein family form silencing complexes and maintain the repressed state, whereas the conversely acting trxG proteins promote transcription and maintain the active and open chromatin mode (for a recent review, see reference 13).Well-known targets for this type of regulation, termed cellular memory, are the homeotic gene clusters whose products determine axial cellular identities in multicellular organisms. In Drosophila melanogaster, the bithorax complex (BX-C) contains the three homeotic genes Ultrabithorax (Ubx), abdominal-A (abd-A), and Abdominal-B (Abd-B). Parasegment-specific cell identity of parts of the thorax and abdomen is achieved by differential and tightly controlled expression of each homeotic gene along the anterior-posterior axis of the developing fly (21,35).The bithorax complex is organized into nine large cis regulatory units (abx/bx, bxd/pbx, and iab-2 to iab-8), which are responsible for the correct parasegment-specific expression patterns of the three homeotic genes. Embryonically acting maternal and segmentation genes set the parasegment-specific expression pattern of homeotic genes. In the cis regulatory sequences, chromosomal elements such as bithoraxoid (bxd),