Impact of Interactions between Su(Hw)-Dependent Insulators on the Transvection Effect in Drosophila melanogaster.

Transvection is a phenomenon of interallelic communication in which enhancers can activate a specific promoter located on a homologous chromosome. Insulators play a significant role in ensuring functional interactions between enhancers and promoters. In the presented work, we created a model where two or three copies of the insulator are located next to enhancers and promoters localized on homologous chromosomes. Using the Su(Hw) insulator as a model, we showed that the functional interaction between a pair of insulators promotes enhancer-promoter trans-interactions. The interaction between the three insulators, on the contrary, can lead to the formation of chromatin loops that sterically hinder the full enhancer-promoter interaction. The results of the work suggest the participation of insulators in the regulation of homologous chromosome pairing and in communication between distant genomic loci.

The BEAF-32 Protein Directly Interacts with Z4/putzig and Chriz/Chromator Proteins in Drosophila melanogaster.

In Drosophila, the BEAF-32, Z4/putzig, and Chriz/Chromator proteins colocalize in the interbands of polytene chromosomes. It was assumed that these proteins can form a complex that affects the structure of chromatin. However, the mechanism of the formation of such a complex has not been studied. We have proved for the first time that the BEAF-32, Z4/putzig, and Chriz/Chromator proteins interact directly with each other and localized the protein domains that provide multiple protein-protein interactions. Based on the data obtained, we developed a model of the mechanism of the formation the BEAF/Z4/Chriz complex and its recruitment to chromatin.

The Chriz Protein Promotes the Recruitment of the Z4 Protein to the STAT-Dependent Promoters.

Proteins Z4/putzig and Chriz/Chromator are involved in the chromatin organization on the promoters of the majority of Drosophila genes. It was shown that the Chriz protein region from aa 273 to 503 is required for the interaction with the Z4 protein. Deletion of this sequence leads to derepression of a number of STAT-dependent genes and development of melanotic tumors in flies. The results of this study suggest that the Chriz protein promotes the recruitment of the Z4 protein to chromatin.

The Functions and Mechanisms of Action of Insulators in the Genomes of Higher Eukaryotes.

The mechanisms underlying long-range interactions between chromatin regions and the principles of chromosomal architecture formation are currently under extensive scrutiny. A special class of regulatory elements known as insulators is believed to be involved in the regulation of specific long-range interactions between enhancers and promoters. This review focuses on the insulators of Drosophila and mammals, and it also briefly characterizes the proteins responsible for their functional activity. It was initially believed that the main properties of insulators are blocking of enhancers and the formation of independent transcription domains. We present experimental data proving that the chromatin loops formed by insulators play only an auxiliary role in enhancer blocking. The review also discusses the mechanisms involved in the formation of topologically associating domains and their role in the formation of the chromosomal architecture and regulation of gene transcription.

Activation of Su(Hw)-Controlled Genes Is Associated with Increase in GAF Binding.

The interaction of the GAF protein with the promoters of neuron-specific genes during activation and repression of transcription was studied. We showed that, while the Su(Hw) protein remains stably associated with the promoters of these genes at different transcriptional state, the GAF protein level is significantly higher when transcription is activated.

Studying Interactions between the Mod(mdg4)-67.2 Protein and Other Mod(mdg4) Isoforms in the Embryonic Cells of Drosophila melanogaster.

It is found that, in embryonic D. melanogaster cells, Mod(mdg4) protein isoforms can interact with each other through BTB domains. However, this nonspecific interaction is destroyed as a result of recruitment of protein complexes to the chromatin sites.

The Role of GC-Rich Sequences from the Promoter Region of the Drosophila melanogaster yellow Gene in the Enhancer- Dependent Activation of Transcription.

It is shown that mutations in two GC-rich sequences (GC-boxes) from the promoter region of the yellow gene during enhancer-dependent transcription activation do not affect the basal level of the yellow gene transcription but destabilize the interaction between the enhancers and the promoter.

LTR sequence of the MDG4 retrotransposon contains the MAD protein binding site that affects the east-dependent repression.

Earlier, we showed in a model system of the yellow gene of D. melanogaster that an increase in the EAST protein concentration leads to repression in bristles, the mechanism of which remained obscure. In this study, an inverted repeat was localized by genetic methods in the long terminal repeat (LTR) sequence of the MDG4 retrotransposon. This repeat includes the binding site for the Mad protein-the key component of the of TGF-ß/BMP signaling cascade. The results of this work suggest that the Mad protein recruits to chromatin a regulatory complex that functionally interacts with the EAST protein. This complex either itself suppresses the yellow gene expression in bristles or moves the transgene to the nuclear regions with a high concentration of transcription repression factors.

Zinc finger domain of Su(Hw) protein is required for the formation of functional Su(Hw)-dependent insulator complex.

This study is devoted to clarifying the role of Mod(mdg4)-67.2 and Su(Hw) proteins in the interaction between Su(Hw)-dependent insulator complexes and identifying the specific domains of the Su(Hw) protein required for insulation or mutual neutralization of insulators. Using genetic techniques and experiments in yeast two-hybrid system, we have demonstrated that the zinc finger domain of the Su(Hw) protein is involved in forming a functional insulator complex and cannot be replaced with the DNA-binding domain of the GAL4 protein.

Mod(mdg4)-58.8, isoform of mod(mdg4) loci, directly interacts with MTACP1A and MTACP1B proteins of Drosophila melanogaster.

As a result of experiments in yeast two-hybrid system, coimmunoprecipitation of proteins from D. melanogaster embryo cell lysate, and immunostaining, it was shown for the first time that Mod(mdg4)-58.8 protein (isoform P), a product of mod(mdg4) locus, directly interacts with mtACP1A and mtACP1B proteins. These proteins are involved in de novo biosynthesis of fatty acids in mitochondria and are required for normal gametogenesis in males and females and, possibly, for the trachea development. This result expands the understanding of the role of mod(mdg4) locus products in the regulation of life activity of the eukaryotic cell.

[The Role of Su(Hw) Protein in Transcription Regulation in Drosophila melanogaster].

Insulators are regulatory DNA elements that modulate the effect of enhancers and silencers on gene transcription. However, the role of the insulator complex proteins in the expression of specific genes remains scarcely studied. In the present study, we examined the role of the Su(Hw)-dependent insulator complex in transcription of the rap, CG32810, and RpS15Aa genes. It was demonstrated that the interaction of Su(Hw) and Mod(mdg4)-67.2 insulator proteins with the terminator regions of the selected genes was dependent on the Su(Hw) factor. At the same time, the CP190 protein also interacts with the promoter and terminator regions in the absence of Su(Hw). In addition, the Su(Hw) protein does not affect the level of transcription and silencing efficiency of the gene models. A possible explanation for these results is the existence of another transcription factor, a protein that is able to recruit CP190 and functionally compensate for the lack of the Su(Hw) protein.

[The nuclear matrix protein EAST affects the transcription of Drosophila melanogaster genes irrespective of the presence of retrotransposon MDG4 sequences].

Our recent study demonstrated that alteration of expression of the east gene affects the transcription of the yellow gene of Drosophila melanogaster. Furthermore, this influence was shown to be associated with the presence of retrotransposon MDG4 sequences in the pre-promoter gene region. In the present study, we analyzed the effects of different concentrations of EAST protein on the expression of different genes of Drosophila. In addition, it was analyzed whether this effect was associated with the presence of MDG4 in the allelic gene variant of interest. It was demonstrated that the effect of EAST protein on the expression of different genes was not always directly associated with the presence of MDG4 sequences. For instance, an increase in the EAST concentration had no effect on the expression of mutant alleles of the achaete-scute complex, some of which contained the MDG4 sequences. Moreover, enhancement of the east expression resulted in the alteration of the phenotypic manifestation of the mutant allele of the cut locus irrespective of the presence of MDG4. Finally, the alteration of the EAST concentrations had no substantial effect on transgene repression if they were inserted either in heterochromatin or in telomeric regions of chromosome 4, as well as on the repression induced by Polycomb group proteins. The data obtained suggested that EAST protein belonged to a new regulatory system, which was common to most of the genes, and repressed transcription of the genes located in the euchromatin regions of the chromosomes.