A heat-shock-activated cDNA encoding GAGA factor rescues some lethal mutations in the Drosophila melanogaster Trithorax-like gene

GAGA factor is an important chromosomal protein involved in establishing specific nucleosome arrays and in regulating gene transcription in Drosophila melanogaster. We developed a transgenic system for controlled heat-shock-dependent overexpression of the GAGA factor 519 amino acid isoform (GAGA-519) in vivo. Efficient production of stable protein from these transgenes provided genetic rescue of a hypomorphic Trithorax-like (Trl) lethal allele to adulthood. Nevertheless, supplemental GAGA-519 did not suppress position effect variegation (PEV), a phenomenon commonly used to measure dosage effects of chromosomal proteins, nor did it rescue other lethal alleles of Trl. The results suggest requirements for the additional isoforms of GAGA factor, of for more precise regulation of synthesis, to carry out the diverse functions of this protein

Chromatin: Ga-ga over GAGA factor

AbstractRecent results suggest that the Drosophila transcriptional activator known as GAGA factor functions by influencing chromatin structure

Clostridium septicum Empyema in an Immunocompetent Woman

We report a case of a Clostridium septicum empyema in an immunocompetent woman following operation for an incarcerated internal hernia. The patient was successfully treated with pleural decortication and an extended course of postoperative antibiotics. This is the first report of such an infection in the medical literature

dSAP18 and dHDAC1 contribute to the functional regulation of the Drosophila Fab-7 element

It was described earlier that the Drosophila GAGA factor [Trithorax-like (Trl)] interacts with dSAP18, which, in mammals, was reported to be a component of the Sin3–HDAC co-repressor complex. GAGA–dSAP18 interaction was proposed to contribute to the functional regulation of the bithorax complex (BX-C). Here, we show that mutant alleles of Trl, dsap18 and drpd3/hdac1 enhance A6-to-A5 transformation indicating a contribution to the regulation of Abd-B expression at A6. In A6, expression of Abd-B is driven by the iab-6 enhancer, which is insulated from iab-7 by the Fab-7 element. Here, we report that GAGA, dSAP18 and dRPD3/HDAC1 co-localize to ectopic Fab-7 sites in polytene chromosomes and that mutant Trl, dsap18 and drpd3/hdac1 alleles affect Fab-7-dependent silencing. Consistent with these findings, chromatin immunoprecipitation analysis shows that, in Drosophila embryos, the endogenous Fab-7 element is hypoacetylated at histones H3 and H4. These results indicate a contribution of GAGA, dSAP18 and dRPD3/HDAC1 to the regulation of Fab-7 function

Distinct Cytoplasmic and Nuclear Fractions of Drosophila Heterochromatin Protein 1: Their Phosphorylation Levels and Associations with Origin Recognition Complex Proteins

The distinct structural properties of heterochromatin accommodate a diverse group of vital chromosome functions, yet we have only rudimentary molecular details of its structure. A powerful tool in the analyses of its structure in Drosophila has been a group of mutations that reverse the repressive effect of heterochromatin on the expression of a gene placed next to it ectopically. Several genes from this group are known to encode proteins enriched in heterochromatin. The best characterized of these is the heterochromatin-associated protein, HP1. HP1 has no known DNA-binding activity, hence its incorporation into heterochromatin is likely to be dependent upon other proteins. To examine HP1 interacting proteins, we isolated three distinct oligomeric species of HP1 from the cytoplasm of early Drosophila embryos and analyzed their compositions. The two larger oligomers share two properties with the fraction of HP1 that is most tightly associated with the chromatin of interphase nuclei: an underphosphorylated HP1 isoform profile and an association with subunits of the origin recognition complex (ORC). We also found that HP1 localization into heterochromatin is disrupted in mutants for the ORC2 subunit. These findings support a role for the ORC-containing oligomers in localizing HP1 into Drosophila heterochromatin that is strikingly similar to the role of ORC in recruiting the Sir1 protein to silencing nucleation sites in Saccharomyces cerevisiae

Impact of Orthologous Gene Replacement on the Circuitry Governing Pilus Gene Transcription in Streptococci

The evolutionary history of several genes of the bacterial pathogen Streptococcus pyogenes strongly suggests an origin in another species, acquired via replacement of the counterpart gene (ortholog) following a recombination event. An example of orthologous gene replacement is provided by the nra/rofA locus, which encodes a key regulator of pilus gene transcription. Of biological importance is the previous finding that the presence of the nra- and rofA-lineage alleles, which are approximately 35% divergent, correlates strongly with genetic markers for streptococcal infection at different tissue sites in the human host (skin, throat).In this report, the impact of orthologous gene replacement targeting the nra/rofA locus is experimentally addressed. Replacement of the native nra-lineage allele with a rofA-lineage allele, plus their respective upstream regions, preserved the polarity of Nra effects on pilus gene transcription (i.e., activation) in the skin strain Alab49. Increased pilus gene transcription in the rofA chimera correlated with a higher rate of bacterial growth at the skin. The transcriptional regulator MsmR, which represses nra and pilus gene transcription in the Alab49 parent strain, has a slight activating effect on pilus gene expression in the rofA chimera construct.Data show that exchange of orthologous forms of a regulatory gene is stable and robust, and pathogenicity is preserved. Yet, new phenotypes may also be introduced by altering the circuitry within a complex transcriptional regulatory network. It is proposed that orthologous gene replacement via interspecies exchange is an important mechanism in the evolution of highly recombining bacteria such as S. pyogenes

The Torso signaling pathway modulates a dual transcriptional switch to regulate tailless expression

The Torso (Tor) signaling pathway activates tailless (tll) expression by relieving tll repression. None of the repressors identified so far, such as Capicuo, Groucho and Tramtrack69 (Ttk69), bind to the tor response element (tor-RE) or fully elucidate tll repression. In this study, an expanded tll expression pattern was shown in embryos with reduced heat shock factor (hsf) and Trithorax-like (Trl) activities. The GAGA factor, GAF encoded by Trl, bound weakly to the tor-RE, and this binding was enhanced by both Hsf and Ttk69. A similar extent of expansion of tll expression was observed in embryos with simultaneous knockdown of hsf, Trl and ttk69 activities, and in embryos with constitutively active Tor. Hsf is a substrate of mitogen-activated protein kinase and S378 is the major phosphorylation site. Phosphorylation converts Hsf from a repressor to an activator that works with GAF to activate tll expression. In conclusion, the GAF/Hsf/Ttk69 complex binding to the tor-RE remodels local chromatin structure to repress tll expression and the Tor signaling pathway activate tll expression by modulating a dual transcriptional switch

Environmental Acidification Drives S. pyogenes Pilus Expression and Microcolony Formation on Epithelial Cells in a FCT-Dependent Manner

Group A Streptococcus (GAS, Streptococcus pyogenes) is a Gram-positive human pathogen responsible for a diverse variety of diseases, including pharyngitis, skin infections, invasive necrotizing fasciitis and autoimmune sequelae. We have recently shown that GAS cell adhesion and biofilm formation is associated with the presence of pili on the surface of these bacteria. GAS pilus proteins are encoded in the FCT (Fibronectin- Collagen-T antigen) genomic region, of which nine different variants have been identified so far. In the present study we undertook a global analysis of GAS isolates representing the majority of FCT-variants to investigate the effect of environmental growth conditions on their capacity to form multicellular communities. For FCT-types 2, 3, 5 and 6 and a subset of FCT-4 strains, we observed that acidification resulting from fermentative sugar metabolism leads to an increased ability of the bacteria to form biofilm on abiotic surfaces and microcolonies on epithelial cells. The higher biofilm forming capacity at low environmental pH was directly associated with an enhanced expression of the genes encoding the pilus components and of their transcription regulators. The data indicate that environmental pH affects the expression of most pilus types and thereby the formation of multicellular cell-adhering communities that assist the initial steps of GAS infection