PubMed Health⌕ Search

Biomedical subjects

V G Corces

Publications and source records attributed to V G Corces.

At least 19 recordsLinked to original sources
PubMed2001

Interactions between the Su(Hw) and Mod(mdg4) proteins required for gypsy insulator function.

The gypsy insulator is thought to play a role in nuclear organization and the establishment of higher order chromatin domains by bringing together several individual insulator sites to form rosette-like structures in the interphase nucleus. The Su(Hw) and Mod(mdg4) proteins are components of the gypsy insulator required for its effect on enhancer-promoter interactions. Using the yeast two-hybrid system, we show that the Mod(mdg4) protein can form homodimers, which can then interact with Su(Hw). The BTB domain of Mod(mdg4) is involved in homodimerization, whereas the C-terminal region of the protein is involved in interactions with the leucine zipper and adjacent regions of the Su(Hw) protein. Analyses using immunolocalization on polytene chromosomes confirm the involvement of these domains in mediating the interactions between these proteins. Studies using diploid interphase cells further suggest the contribution of these domains to the formation of rosette-like structures in the nucleus. The results provide a biochemical basis for the aggregation of multiple insulator sites and support the role of the gypsy insulator in nuclear organization.

Animals↗
PubMed2001

Protein determinants of insertional specificity for the Drosophila gypsy retrovirus.

The gypsy retrovirus invades the germ line of Drosophila females, inserting with a high frequency into the ovo locus. Gypsy insertion sites in ovo are clustered within a region in the promoter of the ovo gene that contains multiple binding sites for the OvoA and OvoB proteins. We found that a 1.3-kb DNA fragment containing this region is able to confer gypsy insertional specificity independent of its genomic location. The frequency of gypsy insertions into the ovo gene is significantly lower in wild-type females than in ovoD1 females. In addition, gypsy insertions in ovoD1 females occur during most stages of germ-line development whereas insertions in wild-type females occur only in late stages. This pattern of temporally specific insertions, as well as the higher frequency of insertion in ovoD1 females, correlates with the presence of the OvoA or OvoD1 proteins. The results suggest that gypsy insertional specificity might be determined by the binding of the OvoA repressor isoform to the promoter region of the gene.

Animals↗
PubMed2001

The gypsy insulator of Drosophila affects chromatin structure in a directional manner.

Chromatin insulators are thought to regulate gene expression by establishing higher-order domains of chromatin organization, although the specific mechanisms by which these sequences affect enhancer-promoter interactions are not well understood. Here we show that the gypsy insulator of Drosophila can affect chromatin structure. The insulator itself contains several DNase I hypersensitive sites whose occurrence is dependent on the binding of the Suppressor of Hairy-wing [Su(Hw)] protein. The presence of the insulator in the 5' region of the yellow gene increases the accessibility of the DNA to nucleases in the promoter-proximal, but not the promoter-distal, region. This increase in accessibility is not due to alterations in the primary chromatin fiber, because the number and position of the nucleosomes appears to be the same in the presence or absence of the insulator. Binding of the Su(Hw) protein to insulator DNA is not sufficient to induce changes in chromatin accessibility, and two domains of this protein, presumed to be involved in interactions with other insulator components, are essential for this effect. The presence of Modifier of mdg4 [Mod(mdg4)] protein, a second component of the gypsy insulator, is required to induce these alterations in chromatin accessibility. The results suggest that the gypsy insulator affects chromatin structure and offer insights into the mechanisms by which insulators affect enhancer-promoter interactions.

Animals↗
PubMed2001

Chromatin insulators and boundaries: effects on transcription and nuclear organization.

Chromatin boundaries and insulators are transcriptional regulatory elements that modulate interactions between enhancers and promoters and protect genes from silencing effects by the adjacent chromatin. Originally discovered in Drosophila, insulators have now been found in a variety of organisms, ranging from yeast to humans. They have been found interspersed with regulatory sequences in complex genes and at the boundaries between active and inactive chromatin. Insulators might modulate transcription by organizing the chromatin fiber within the nucleus through the establishment of higher-order domains of chromatin structure.

Animals↗
PubMed2000

Phosphorylation of histone H3 correlates with transcriptionally active loci.

Posttranslational modifications of the N-terminal tails of the core histones within the nucleosome particle are thought to act as signals from the chromatin to the cell for various processes. The experiments presented here show that the acetylation of histones H3 and H4 in polytene chromosomes does not change during heat shock. In contrast, the global level of phosphorylated H3 decreased dramatically during a heat shock, with an observed increase in H3 phosphorylation at the heat shock loci. Additional experiments confirm that this change in phosphorylated H3 distribution is dependent on functional heat shock transcription factor activity. These experiments suggest that H3 phosphorylation has an important role in the induction of transcription during the heat shock response.

Acetylation↗
PubMed2000

A chromatin insulator determines the nuclear localization of DNA.

Chromatin insulators might regulate gene expression by controlling the subnuclear organization of DNA. We found that a DNA sequence normally located inside of the nucleus moved to the periphery when the gypsy insulator was placed within the sequence. The presence of the gypsy insulator also caused two sequences, normally found in different regions of the nucleus, to come together at a single location. Alterations in this subnuclear organization imposed by the gypsy insulator correlated with changes in gene expression that took place during the heat-shock response. These global changes in transcription were accompanied by dramatic alterations in the distribution of insulator proteins and DNA. The results suggest that the nuclear organization imposed by the gypsy insulator on the chromatin fiber is important for gene expression.

Animals↗
PubMed1999

The lawc gene is a new member of the trithorax-group that affects the function of the gypsy insulator of Drosophila.

Mutations in the lawc gene result in a pleiotropic phenotype that includes homeotic transformation of the arista into leg. lawc mutations enhance the phenotype of trx-G mutations and suppress the phenotype of Pc mutations. Mutations in lawc affect homeotic gene transcription, causing ectopic expression of Antennapedia in the eye-antenna imaginal disc. These results suggest that lawc is a new member of the trithorax family. The lawc gene behaves as an enhancer of position-effect variegation and interacts genetically with mod(mdg4), which is a component of the gypsy insulator. In addition, mutations in the lawc gene cause alterations in the punctated distribution of mod(mdg4) protein within the nucleus. These results suggest that the lawc protein is involved in regulating the higher-order organization of chromatin.

Animals↗
PubMed1998

A hotspot for the Drosophila gypsy retroelement in the ovo locus.

The Drosophila retroelement gypsy has a number of unusual features including an unusual LTR terminal sequence and an apparent target sequence preference. The ovo locus is a known hotspot for gypsy insertion. We examined the target sequence preference of gypsy within ovo by isolating 26 new insertions and sequencing the gypsy/ovo junctions. Insertions were found at multiple sites within the ovo locus. The insertions clustered within an approximately 150 bp region in the non-translated region of the ovo beta transcript, with most insertions falling within the first intron. There were seven sites of insertion within this region and these mostly conform to the consensus sequence YRYRYR (where Y = pyrimidine and R = purine). However, this target sequence is at best necessary but not sufficient to specify a hotspot, as there were several other sequences conforming to this consensus in the ovo locus that were not hit. The results indicate that gypsy may have a higher degree of target specificity than most infectious LTR retroelements.

Animals↗
PubMed1998

Polycomb and trithorax group proteins mediate the function of a chromatin insulator.

Chromatin boundaries or insulator elements affect the interaction between enhancers and promoters. The gypsy insulator contains two proteins, Su(Hw) and Mod(mdg4). Both proteins colocalize on several hundred sites on polytene chromosomes and are distributed in a punctated pattern in the nuclear matrix. Mutations in mod(mdg4) have properties characteristic of a trxG gene. In addition, mutations in trxG genes enhance insulator effects on adjacent enhancers, whereas mutations in Pc have the opposite result. These alterations correlate with changes in the pattern of nuclear localization of insulator components. The results suggest a model in which PcG and TrxG proteins regulate insulator function by establishing higher order domains of chromatin organization required for the assembly of functional insulators at the nuclear matrix.

Animals↗
PubMed1997

Interaction of Wnt and a Frizzled homologue triggers G-protein-linked phosphatidylinositol signalling.

In Drosophila, members of the frizzled family of tissue-polarity genes encode proteins that are likely to function as cell-surface receptors of the type known as Wnt receptors, and to initiate signal transduction across the cell membrane, although how they do this is unclear. We show here that the rat protein Frizzled-2 causes an increase in the release of intracellular calcium which is enhanced by Xwnt-5a, a member of the Wnt family. This release of intracellular calcium is suppressed by an inhibitor of the enzyme inositol monophosphatase and hence of the phosphatidylinositol signalling pathway; this suppression can be rescued by injection of the compound myo-inositol, which overcomes the decrease in this intermediate caused by the inhibitor. Agents that inhibit specific G-protein subunits, pertussis toxin, GDP-beta-S and alpha-transducin also inhibit the calcium release triggered by Xwnt-5a and rat Frizzled-2. Our results indicate that some Wnt proteins work through specific Frizzled homologues to stimulate the phosphatidylinositol signalling pathway via heterotrimeric G-protein subunits.

Animals↗
PubMed1997

Penelope, a new family of transposable elements and its possible role in hybrid dysgenesis in Drosophila virilis.

A hybrid dysgenesis syndrome occurs in Drosophila virilis when males from an established laboratory strain are crossed to females obtained from the wild, causing the simultaneous mobilization of several different transposable elements. The insertion sequence responsible for the mutant phenotype of a dysgenic yellow allele has been characterized and named Penelope. In situ hybridization and Southern analyses reveal the presence of more than 30 copies of this element in the P-like parental strain, whereas Penelope is absent in all M-like strains tested. Penelope contains one 2.5-kb-long ORF that could encode products with homology to integrase and reverse transcriptase. Northern analysis and whole-mount in situ hybridization show strong induction of a 2.6-kb RNA in the ovaries of dysgenic females that is expressed at very low levels in the parental strains or in the progeny from the reciprocal cross. Injection of Penelope-containing plasmids into preblastoderm embryos of an M-like strain results in mutant progeny caused by insertion of Ulysses and perhaps other transposons, suggesting that Penelope expression might be responsible for the observed dysgenesis syndrome and the simultaneous mobilization of other transposable elements.

Amino Acid Sequence↗
PubMed1997

Characterization of functional domains of the su(Hw) protein that mediate the silencing effect of mod(mdg4) mutations.

The suppressor of Hairy-wing [su(Hw)] protein represses enhancer function in a unidirectional fashion: enhancers segregated from the promoter by the su(Hw) binding region are rendered inactive. whereas those in the same domain are unaffected. In the case of the gypsy-induced y2 allele, the repressive effect of su(Hw) is rendered bidirectional in mod(mdg4) mutant flies, and all enhancers of the affected gene become inactive. This silencing of enhancer elements might be due to exposure of specific domains of su(Hw) when the mod(mdg4) protein is absent. Two of three regions of su(Hw) that are located adjacent to the leucine zipper motif and are conserved across Drosophila species are necessary for both the unidirectional and bidirectional repression of transcription by su(Hw). In contrast, two acidic domains that are dispensable for the unidirectional repression of enhancer elements are critical for the bidirectional silencing of enhancer activity observed in mutants lacking functional mod(mdg4) protein.

Animals↗
PubMed1997

Insertions of hybrid P elements in the yellow gene of Drosophila cause a large variety of mutant phenotypes.

A series of yellow mutations associated with a great variety of tissue-specific phenotypes were obtained from several highly unstable Drosophila melanogaster strains carrying the gypsy-induced y2 allele. These mutations are caused by insertion of additional DNA sequences of variable size 69 bp upstream of the yellow transcription start site. These sequences are flanked by identical copies of a deleted 1.2-kb P element arranged in the same or inverted orientation. The central part of the inserted element consists of genomic sequences originating from different regions of the X chromosome. The mutant phenotype caused by these chimeric elements depends on the nature of the sequences present either in the P element or in the central part of the insertion, suggesting that these sequences are able to affect expression of the yellow gene. In addition, sequences present in the central region of the insertions strongly modify the effects of the gypsy-bound suppressor of Hairy-wing [su(Hw)] and modifier of mdg4 [mod(mdg4)] proteins on yellow transcription. Analyses of these mutations give new insights into the mechanisms by which su (Hw) and mod(mdg4) affect enhancer function.

Alleles↗
PubMed1997

Transposable element-host interactions: regulation of insertion and excision.

Transposable elements propagate by inserting into new locations in the genomes of the hosts they inhabit. Their transposition might thus negatively affect the fitness of the host, suggesting the requirement for a tight control in the regulation of transposable element mobilization. The nature of this control depends on the structure of the transposable element. DNA elements encode a transposase that is necessary, and in most cases sufficient, for mobilization. In general, regulation of these elements depends on intrinsic factors with little direct input from the host. Retrotransposons require an RNA intermediate for transposition, and their frequency of mobilization is controlled at multiple steps by the host genome by regulating both their expression levels and their insertional specificity. As a result, a symbiotic relationship has developed between transposable elements and their host. Examples are now emerging showing that transposons can contribute significantly to the well being of the organisms they populate.

Animals↗