The enhancer of trithorax and polycomb corto interacts with cyclin G in Drosophila

Background

Polycomb (PcG) and trithorax (trxG) genes encode proteins involved in the maintenance of gene expression patterns, notably Hox genes, throughout development. PcG proteins are required for long-term gene repression whereas TrxG proteins are positive regulators that counteract PcG action. PcG and TrxG proteins form large complexes that bind chromatin at overlapping sites called Polycomb and Trithorax Response Elements (PRE/TRE). A third class of proteins, so-called “Enhancers of Trithorax and Polycomb” (ETP), interacts with either complexes, behaving sometimes as repressors and sometimes as activators. The role of ETP proteins is largely unknown.

Methodology/Principal Findings

In a two-hybrid screen, we identified Cyclin G (CycG) as a partner of the Drosophila ETP Corto. Inactivation of CycG by RNA interference highlights its essential role during development. We show here that Corto and CycG directly interact and bind to each other in embryos and S2 cells. Moreover, CycG is targeted to polytene chromosomes where it co-localizes at multiple sites with Corto and with the PcG factor Polyhomeotic (PH). We observed that corto is involved in maintaining Abd-B repression outside its normal expression domain in embryos. This could be achieved by association between Corto and CycG since both proteins bind the regulatory element iab-7 PRE and the promoter of the Abd-B gene.

Conclusions/Significance

Our results suggest that CycG could regulate the activity of Corto at chromatin and thus be involved in changing Corto from an Enhancer of TrxG into an Enhancer of PcG.     

Structural analysis of point mutations in the Hairless gene and their association with the activity of the Hairless protein

The Notch signaling pathway (NSP) is an important intercellular communication mechanism that regulates embryo development and adult physiological functions. The Hairless (H) protein is a powerful antagonist of the NSP by its interaction with the Suppressor of Hairless (Su[H]) protein, recruiting the corepressors Gro and CtBP. In the present work, we examined the role of several important amino acids in different H protein domains analyzing four mutant lines of Drosophila melanogaster. The mutant alleles were evaluated by single-strand conformational polymorphism (SSCP) analysis and we located mutated regions at different positions along the sequence of the Hairless gene.     

The influence of a reduced gibberellin biosynthesis and nitrogen supply on the morphology and anatomy of leaves and roots of tomato (Solanum lycopersicum)

We investigated how the differences in growth and morphology, between fast-growing wildtype (Wt) tomato ( Solanum lycopersicum L.) plants and slow-growing gibberellin (GA) deficient W335 mutants, were reflected in cell numbers and cell sizes. We also studied whether the differences between the Wt and the low-GA mutant would persist at a growth-limiting supply of nitrate. Both a low endogenous GA concentration and a low supply of nitrate reduced the number and size of leaf cells, whereas they increased the size and number of root cortex cells. The effects of low N-supply on the size and number of leaf and root cells did not depend on endogenous GA concentrations. The mutant's higher allocation to roots seemed to be the result of the strongly reduced growth of the shoot.     

Susceptibility of the Hymenopteran Parasitoids Apoanagyrus ( = Epidinocarsis ) lopezi (Encyrtidae) and Phanerotoma sp. (Braconidae) to the Entomopathogenic Fungus Metarhizium anisopliae var. acridum (Deuteromycotina: Hyphomycetes)

Laboratory and so-called extended laboratory bioassays were conducted in Benin, West Africa, to investigate the pathogenicity and virulence of the entomopathogenic fungus Metarhizium anisopliae var. acridum , a biocontrol agent against locusts and grasshoppers, to two hymenopteran parasitoids, Apoanagyrus ( = Epidinocarsis ) lopezi and Phanerotoma sp. Treatments were carried out under simulated field conditions at standard field dose rates of 2.5 and 5.0 ×10 12 conidia ha -1 . Test organisms were continuously (3 weeks) exposed to spray residues in artificial or simulated natural environments. The standard strain IMI 330 189 of the mycopesticide Green Muscle caused a significant reduction of 24% in the longevity ( = average survival time, AST) of A. lopezi , relative to the untreated control. Mycosis was confirmed in 16% of all cadavers. AST was shorter under low relative humidity (RH) conditions, and these conditions seemed to enhance susceptibility to fungal infection. However, this effect was only marginally significant. In contrast, average longevity of untreated A. lopezi was slightly yet significantly shorter at low RH (50-60%) than at high RH (80-90%). In the extended laboratory assay, the same isolate had no significant effect on mortality, parasitoid emergence ( = beneficial capacity) and sex ratio. In a further screening test with isolates IIBC I91 609, IIBC I93 833 and IMI 330 189 (reference), no infection of A. lopezi was confirmed. Similarly, Phanerotoma sp. was not susceptible to IMI 330 189. It is concluded that mycopesticides based on the three strains tested pose a low risk to parasitic hymenopterans under field conditions.     

Generation of New Hairless Alleles by Genomic Engineering at the Hairless Locus in Drosophila melanogaster

Hairless (H) is the major antagonist within the Notch signalling pathway of Drosophila melanogaster. By binding to Suppressor of Hairless [Su(H)] and two co-repressors, H induces silencing of Notch target genes in the absence of Notch signals. We have applied genomic engineering to create several new H alleles. To this end the endogenous H locus was replaced with an attP site by homologous recombination, serving as a landing platform for subsequent site directed integration of different H constructs. This way we generated a complete H knock out allele H ^attP, reintroduced a wild type H genomic and a cDNA-construct (H ^gwt, H ^cwt) as well as two constructs encoding H proteins defective of Su(H) binding (H ^LD, H ^iD). Phenotypes regarding viability, bristle and wing development were recorded, and the expression of Notch target genes wingless and cut was analysed in mutant wing discs or in mutant cell clones. Moreover, genetic interactions with Notch (N ⁵⁴¹⁹) and Delta (Dl ^B2) mutants were addressed. Overall, phenotypes were largely as expected: both H ^LD and H ^iD were similar to the H ^attP null allele, indicating that most of H activity requires the binding of Su(H). Both rescue constructs H ^gwt and H ^cwt were homozygous viable without phenotype. Unexpectedly, the hemizygous condition uncovered that they were not identical to the wild type allele: notably H ^cwt showed a markedly reduced activity, suggesting the presence of as yet unidentified regulatory or stabilizing elements in untranslated regions of the H gene. Interestingly, H ^gwt homozygous cells expressed higher levels of H protein, perhaps unravelling gene-by-environment interactions.     

Über die Wirkung verschiedener Faktoren,insbesondere narkotisierender Substanzen auf die vitale Methylenblaufärbung bei in vitro gezüchteten Fibrocyten

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