[Aryl-hydrocarbon receptor as a potential target for anticancer therapy]

Aryl-hydrocarbon receptor (Aryl Hydrocarbon Receptor, AHR) is a ligand-dependent transcription factor, whose functions are related to xenobiotic detoxification, response to inflammation, and maintenance of tissue homeostasis. Recent investigations suggest that AHR also plays an important role in the processes of carcinogenesis. Increased expression of AHR is observed in several types of tumors and tumor cell lines. In addition, it turned out that the composition of pharmaceutical drugs used in oncotherapy includes some ligands AHR. These facts allow us to consider an aryl-hydrocarbon receptor as a potential target for anticancer therapy, especially for the treatment of severe cancers whose treatment options are very limited or do not exist at all. In this review the examples of AHR ligands' effect on tumor cell cultures and on model mice lines with AHR-dependent response are discussed.

[Overlapping genes and antisense transcription in eukaryotes]

Numerous studies showed that overlapping genes are fairly common elements of genome organization, not only in viruses and prokaryotes but also in eukaryotes. At the same time, the regulatory mechanisms of overlapping gene expression, as well as the functional relevance of antisense transcription, are still relatively unknown. This review describes the history of the discovery of regulatory antisense RNAs, the types of gene overlap, and the putative mechanisms of their functioning. In conclusion, the critical views of different authors on the problem of detecting overlapping genes and an evaluation of the level of antisense transcription are presented.

[Effect of mutations in lawc/Trf2 gene on development of chromocenter and chromosome disjunction in Drosophila melanogaster]

In Drosophila, one of the genes of the lawc/Trf2 (leg-arista-wing complex/TBP-related factor 2) complex encodes an alternative basic transcription factor homologous to the TRF2 protein in vertebrates and human and belongs to a conservative Tbp (TATA box-binding protein) gene family. In the present study, reasons for the high frequency of chromosome nondisjunction were studied among descendants of mutants from 18 lines with a decreased expression of the TRF2 protein. It was determined that the suppression of the TRF2 expression violates the development of a compact chromocenter and the correct approach of homologous chromosomes (in germinative and somatic cells). The possibility of the participation of TRF2 in the evolutionary genetically programmed process of sex-ratio violation, which is typical of a number of animal species, is discussed.

[Influence of hairpin RNA, specific to the gene lawc, on expression of overlapping genes of the lawc/Trf2 complex in D. melanogaster]

We used a genetic system of the gene complex leg-arista-wing complex/TBP related factor 2 (lawc/Trf2) as a suitable model for in vivo study of operational characteristics of divergent overlapping genes. We established lines of transgenic fruit flies carrying constructs capable of expressing hairpin RNA directed at post-transcriptional suppression of the mRNA gene lawc by way of RNA-interference. The attempt to artificially suppress lawc-transcripts caused a rise in the level of expression of the gene lawc by several times. It is shown that change in the concentration of lawc-transcripts can affect the concentration of Trf2 transcripts. Possible mechanisms of regulation of expression of the overlapping genes studied are discussed.

[D4 family genes in vertebrates: genomic organization and expression]

A family of closely related genes, named the d4 family, has been previously identified in mammals. It comprises three genes encoding structurally related proteins. The hallmark of the family is d4 domain--a double-paired finger motifthat consists of two tandemly arranged PHD finger domains. These genes are expressed in various tissues and at various developmental stages. Two of those, neuro-d4 and cer-d4, are strictly neurospecific and their expression is developmentally regulated. Another gene, ubi-d4/Requiem is ubiquitously expressed in all embryonic and adult tissues at the same levels. d4 family genes are evolutionary conserved. Human, mouse, rat, and chicken d4 genes have been cloned. The only d4-like gene was found in the genome of nematode C. elegans. The sole member of d4 family was identified also in the genome of D. melanogaster. However, d4 genes are not believed to be present in the genomes of prokaryotes and yeast. This review describes genomic organization and expression ofd4family genes in different organisms.

[Recovery of genomic regions affecting lawc/Trf2 expression during Drosophila melanogaster development]

Leg-arista-wing complex (lawc) mutations affect the expression of D. melanogaster proteins homologous to a human basic transcription factor, TBP (TATA-box binding protein) Related Factor 2 (TRF2), specifically involved in development. The paper for the first time reports the application of genetic screens for various genomic regions to recover genetic interactions between the lawc/Trf2 gene and other genes and genetic loci by using Deficiency Kit lines with small deletions in total providing maximal coverage of the genome. The deletion mapping allowed us to recover 26 genomic regions that, when deleted, are lethal or modify the mutant phenotype due to a decreased TRF2 expression level. These deletions could be useful in identifying both novel TRF2 targets and its positive and negative regulators. There is evidence that TRF2 can be a component of high molecular DNA Replication-related Element Factor (DREF)- and Nucleosome Remodeling Factor (NURF)-containing complexes. The present study for the first time reports new genetic interactions of lawc/Trf2 with genes that encode basic and specific transcription factors. In most cases, if mutated, those genes caused developmental defects or death of progeny. However, in the case of the e(y) 1 gene, coding for the Taf9 transcription factor, only the male reproductive system is impaired when the lawc/Trf2 phenotype is associated with a e(y)l gene mutation. Mutant lawc(p1)e(y)1(u1) males become infertile due to primary spermatocyte maturation arrest and impaired premeiotic chromosome condensation in germ cells.

[Gene expression modulation is an evolutionary resource of adaptive alterations in the morphogenesis of insect limbs]

Hypomorphic mutations have been investigated of the genes spineless (ss), Distal-less (Dll), leg-arista-wing complex/TBP-related factor 2(lawc/Trf2), CG5017, and hsp 70 in order to explore the effects of their expression level on the formation of distal structures of antenna and legs of Drosophila melanogaster. We demonstrated the effect of the CG5017, hsp 70, Dll, and lawc gene transcription level on phenotypic manifestation of the ss gene mutation and the involvement of these genes into morphogenesis regulation of Drosophila melanogaster limbs. The total decrease in the level of the CG5017, hsp 70, Dll, and laws gene expression level was shown to promote a loss of the segmented pattern of distal structures of legs and antennae and a reversion of Drosophila limb morphogenesis to the evolutionarily earlier progenitors of insects. A hypothesis is proposed considering limb morphogenesis of insects as an evolutionary ancient process of formation of amorphous-crystal chitin structures with catalytically modifying participation of gene expression products.

[Interaction of the ss and CG5017 genes in the regulation of morphogensis of limbs in Drosophila melanogaster]

The influence of the P-element built into the area of the CG5017 gene on the mutation of the spineless (ss) gene was studied. It was shown that the insertion of the P-element decreased the level of transcription of CG5017 approximately twofold. Modulation of the level of transcription of the CG5017 gene helped demonstrate, for the first time, its influence on the phenotypic manifestation of the mutation of the ss gene, which shows their interaction in the process of regulation of morphogenesis of limbs in Drosophila melanogaster.

[Morphogenetic movement of cells in embryogenesis of Drosophila melanogaster: mechanism and genetic control]

Morphogenetic movement of cells is of significant importance in embryogenesis. It is necessary to identify the final position and configuration of the embryoTs tissues and share the positional information in differentiation. The healing of tissular injuries happens in the adult organism due to the cell layers' movement, and the directed macrophages migration to the nidus of infection assists the neutralization of inflammatory processes. Owing to the good level of knowledge, the fruit fly D. melanogaster is a perfect model object for the study of morphogenetic events in embryogenesis in connection with the cells movement. The description of Drosophila embryogenesis, mechanisms of ventral furrow formation, elongation of the germ band, and its contraction accompanied by dorsal closure was given. During these processes the movement of epithelial cells and the entire epithelial strata happens. The information about the genetic regulation of morphogenetic movement of D. melanogaster taking into consideration the scale of evolutionary conservatism of the cascades of the main signal, which control these processes in vertebrates, is presented.

[Source of asymmetry in ontogeny: early polarization of the germline cyst and oocyte in Drosophila]

One or more body axes are already formed in the egg in many vertebrates and invertebrates. In Drosophila, the anteroposterior and dorsoventral axes are determined during oogenesis owing to the asymmetric localization of the bicoid, oskar, and gurken mRNAs in the oocyte (prospective egg). The localization of these transcripts depends on the polarized organization of the oocyte cytoskeleton and, consequently, the oocyte polarity. Initial asymmetry, leading to the oocyte polarity, is established in early ontogeny, during oocyte determination. The review considers the steps of early polarization and oocyte differentiation in Drosophila, the genetic control of these processes, and the findings that suggest an early oocyte polarity for vertebrates.

[Overexpression of a novel gene toothrin in Drosophila]

A newly found locus of the Drosophila melanogaster genome, named toothrin (tth) has been used to study the role of the conserved domain 2/3 of genes from the d4 family. In contrast to the 2/3 domain of all vertebrates studied (including humans), which is always accompanied by the d4 domain, the tth gene contains the sequence encoding the 2/3 domain but lacks that encoding the d4 domain. The tth gene overexpression has been studied using the two-component system UAS-GAL4. It has been demonstrated that the tth overexpression at the third-instar larval (prepupal) stage decreases survival rate, simultaneously causing a substantial deceleration of development in Drosophila. It is known that the change of developmental stages in Drosophila is controlled by the rates of the expression of ecdysteroid and juvenile hormones (JHs). It is supposed that the overexpression of the tth gene causes either a shift in the ecdysterone-to-JH ratio (through a decreased JH decay rate or a delayed initiation of ecdysone synthesis) or a deceleration of the release of ecdysterones synthesized.

[Use of a genetic system of the chimeric protein P-Ph in the repression of gene transcription of the leg-arista-wing complex in Drosophila]

Preliminary analysis of the leg-arista-wing complex (lawc) gene region in the corresponding mutants revealed P element insertion in the transcribed region of this locus. To demonstrate the main role of P element insertion in the complex pleiotropic phenotypic manifestation of the lawc gene, a system using P-Ph chimeric protein and based on the P-mediated repression of the lawc in vivo transcription was applied. As a result, extreme lawc-mutant phenotypes were obtained and examined. The P-Ph-mediated decrease of the level of the lawc gene transcription was also demonstrated.

Cerd4, third member of the d4 gene family: expression and organization of genomic locus

Two members of the d4 family of presumptive transcription modulators, neuro-d4 (Neud4) and ubi-d4/Requiem (Req), have been characterized previously. We cloned and characterized the third member of this gene family, cer-d4 (Cerd4), from chicken and mouse cDNA libraries. The expression patterns of Cerd4 gene in both species are similar and more restricted than expression patterns of other two d4 genes. The main sites of Cerd4 expression are retina and cerebellum, where multiple transcripts could be detected. Two major types of Cerd4 proteins are a full-length isoform possessing all domains characteristic to the d4 family and truncated XZ isoform without C-terminal tandem of PHD fingers. The developmental kinetics of expression of these isoforms is different. The intron/exon structure of human Cerd4 gene is similar to that of neuro-d4 and ubi-d4/Requiem genes, but most introns of Cerd4 gene are much larger than the corresponding introns of the other two genes.

[Study of the olfactory response in the Drosophila homeotic mutant leg-aristae-wing complex gene]

Antennae are known to be olfactory organs in Drosophila. The leg-aristae-wing complex (lawc) mutation causes a homeotic transformation of the arista (the fifth element of antenna) into tarsal elements. To test how the homeotic transformation of the arista into the tarsus can affect behavior, we studied the olfactory response in the lawc mutants. The data were carefully processed by statistical methods. In spite of a low penetrance of the trait of arista transformation, the mutant flies were found to be approximately half as perceptible to attractant odors than the wild-type flies.

[A novel trans-regulatory locus in Drosophila]

A new trans-regulatory gene, leg-arista-wing complex (lawc), was earlier identified in a system of prolonged genetic instability induced by transpositions of structurally different mobile genetic elements, the P element and MDG Stalker. Mutations of this gene alter expression of many loci, including the achaete and scute proneural genes and the cut locus coding for a homeobox-containing protein. A product of lawc is involved in regulating expression of white. This role is played in cooperation with the product of Zeste which provides for a contact between the white promoter and enhancer. A possible role of the new locus in organogenesis, neurogenesis, and embryonic development is discussed on the basis of experimental findings.

[Taste sensitivity in homeotic mutants of the drosophila leg-arista-wing complex]

It is well established that taste chemoreceptors in Drosophila are located on the tarsi of the first leg pair. In order to investigate the influence of the novel homeotic arista-tarsus transformation on behavior, an analysis of taste perception in the lawc-mutants, characterized by the transformation of the arista into tarsus elements, was carried out. The data were subjected to thorough statistical treatment. It was shown that elements of an additional leg that appeared as a result of homeotic transformation of the arista were sensitive to gustatory stimuli. Analysis of the innervation of the homeotic organs by means of cobalt staining of afferent projections showed that the afferents starting from the homeotic leg reached the thoracic ganglion.

[Genomic organization of the murine neuro-d4 gene]

As the first step toward obtaining the null mutation or knock out of the neuro-d4 gene, we isolated phages containing fragments of the gene from a mouse genomic library. The nucleotide sequence of a region of the gene more than 10 kb in size was determined.

hobo-induced rearrangements are responsible for mutation bursts at the yellow locus in a natural population of Drosophila melanogaster

In 1981 recurrent local bursts of mutability of the yellow gene were observed in a natural population of Drosophila melanogaster from Uman' (Ukraine). A series of y2-like mutations in the yellow gene were recovered during the period 1982 to 1991. Most of the mutants display the y2-phenotype, i.e. mutant yellow color of wings and body cuticle. Ninety-nine y2 mutants were shown to be generated by an inversion that occurred between two hobo elements, one located 129 bp from the start site of yellow transcription, and the other in the distal telomere region. The y2 phenotype was caused by the separation of the body and wing enhancers from the transcription unit. Many of the y2-like alleles were highly unstable and reverted to y+, which again, gave rise to y2-like mutants. We found that the y2-->y+-->y2 transitions were generated by repeated inversions between the two hobo elements mentioned. The y2 and y+ alleles lost their instability after deletion of the hobo element present at the tip of the X chromosome.

[Role of the lawc(p1) mutation in the regulation of the white locus expression in Drosophila]

The lawcp1 mutation of the leg-arista-wing complex (lawc) gene alters expression of three proneural loci: achaete, scute, and cut. In combination with the product of the zeste (z) gene, the product of the lawc gene regulates expression of the white (w) gene. The -w B3 mutation was genetically analyzed in compounds with various z and w mutations and dominant mutations modifying the z-w interaction. The results showed that lawcp1 can enhance the transvection effect. The lawc gene was assumed to regulate expression of the white locus at the level of chromatin condensation.

[Genetic analysis of the lawc(p1) mutation in combination with different alleles of AS-C genes in Drosophila]

Phenotypic expression of mutations within the leg-aristal-wing complex (lawc) locus involves alteration of the number and location of macrochaetae. In Drosophila, development of macrochaetae depends on products of the two proneural genes, achaete (ac) and scute (sc), constituents of the approximately 90-kb ac-sc gene complex (AS-C). Untranscribed regions of AS-C involve enhancer-like cis-elements that are responsible for the local combination of some factors specifically determining expression of the ac-sc genes in larval imaginal discs of Drosophila. In the present work, the frequency of appearance of additional macrochaetae was tested to analyze phenotypic exhibition of the temperature-sensitive lawcp1 allele. This mutation was also genetically analyzed in combination with various AS-C alleles involving alterations of transcribed or cis-regulatory regions of this gene complex. A hypothesis that the lawc gene encodes a factor determining the specific expression of the ac-sc genes is discussed.

[Differential characteristics of the temperature-sensitive period of the lawcp1 mutation on the basis of macrochaetae overexpression in Drosophila]

Temperature-sensitive periods (TSPs) of lawcpl mutations were studied via the frequencies of arising of extras macrochaetae for each macrochaetae type separately. TSPs for the formation of extras macrochaetae of original classes were unevenly distributed within larval instars II and III. It was found that macrochaetae of different types differed from one another in their temperature sensitivity. The TSP of development of macrochaetae belonging to new ectopic classes was multiphase, with the first phase at larval instar II, and the second phase, at the prepupal to early pupal stage. It is assumed that in Drosophila, the products of the lawc gene participate, along with other genes, in the development of the nervous system through regulation of ac-sc expression, both in proneural clusters and outside them.

[Determination of a temperature-sensitive period of the new mutation lawc(P1) in Drosophila melanogaster]

Determination of the period of temperature sensitivity in the temperature-sensitive allele of the regulatory lawc(P1) mutation was performed. Homeotic transformation of arista into tarsus, frequency of leg deformation, and bristle superexpression were examined. The sensitive periods were detected using reciprocal changes of cultivation temperature from 28 to 17 degrees C and from 17 to 28 degrees C. The temperature-sensitive period (TSP) for arista transformation was shown to manifest polyphasic expression and sexual dimorphism. In females, it occurred in late third instar larvae (the first phase) and prepupae (the second stage); in males, it includes the whole period from the late third instar larva upto and including prepupa. TSP for the frequency of deformed legs was polyphasic and took place during the third larval instar (the first phase) and prepupa stage (the second one). TSP for bristle superexpression occurred during a single interval from the late third larval instar until the early prepupa stage. The products of the lawc gene are assumed to play a role both in the cell proliferation in the legs of antennal and imaginal discs and in the control of bristle expression at the final stages of Drosophila ontogeny.

Intragenic suppression: Stalker, a retrovirus-like transposable element, can compensate for a deficiency at the cut locus of Drosophila melanogaster

A number of mutations at the cut locus were induced by non-precise excision of a silent P-element insertion which resulted in deletions at the regulatory region of the locus. Unexpectedly, a reversion of one of these mutations was found, which appears as a result of insertion of Stalker (a retrovirus-like mobile element) near the 1.3 kb deletion. Thus an insertion of a retrovirus-like mobile element can suppress the deficiency at the regulatory region of a gene.

[A new allele variant of ssa and its participation in regulating the proliferation of the stem elements of the leg and antenna imaginal disks in Drosophila melanogaster]

Using a highly mutable FM/w oc system, we have established a new allele of ssa40aSc mutation whose phenotype is identical to ssa40aNs compound described in the literature. The following features are characteristic of the ssa40aSc flies phenotype: (1) the increased number of sex comb teeth, (2) complete fusion of tarsal segments, and (3) the decreased bristle size corresponding to that of ss flies. The first two features are evidence for the impaired stem cell proliferation in the antennal and leg imaginal discs which are determined to form distal structures. This assumption was experimentally confirmed when we transplanted leg imaginal discs from III instar larvae of different age into prepupae. The observed phenomenon is probably due to the defects of the Antp and Pc translation products binding site in the ss locus.

A novel transposition system in Drosophila melanogaster depending on the Stalker mobile genetic element

Crosses between the Drosophila melanogaster y2sc1waG strain or some of its derivatives and the FM4 strain yielded insertional mutagenesis with a frequency of 10(-3)-10(-4). The system differs in several respects from the known cases of hybrid dysgenesis: (i) it does not depend on the direction of a cross; (ii) destabilization continues for a long time after initial crosses; (iii) mutations may occur at different stages of development. The mutation in the yellow locus has been cloned and found to depend on insertion into the coding region of the gene of a novel mobile genetic element designated as Stalker. The sequencing of Stalker termini reveals 405 bp direct repeats (LTRs) and a target 3 bp duplication, as well as some other sequences typical of retrovirus-like retrotransposons. The number of Stalker copies per genome and chromosomal localization vary among D. melanogaster strains. Before crosses, the location of Stalker on chromosomes is fairly stable in a particular strain but thereafter numerous changes in Stalker distribution take place. Most novel substrains are internally heterogenous which is indicative of the continuing Stalker transposition. Other mobile elements tested do not move. Possibly, only Stalker is mobilized in the system. Many known and novel mutations have been obtained. Comparison of their genetic localization with Stalker distribution suggests that the majority of them have been induced by the Stalker insertion.

Mobile genetic elements in Drosophila melanogaster (recent experiments)

Recent data obtained in the authors' laboratories concerning the behaviour of mobile genetic elements of Drosophila melanogaster are reviewed. It was found that the mobile element jockey represents the typical LINE element. It is efficiently transcribed in D. melanogaster cells in flies and in culture. Transcription is initiated from the +1 nucleotide of jockey and depends on an internal promoter. This is the first case of an internal promoter being used by RNA polymerase II. Several events which take place during the transposition bursts in ctMR2 family of strains were described. Among them are the removal of mobile dispersed genetics (mdg) elements (with solo long terminal repeat (LTR) remaining at the site of excision), complete removal of an mdg element, and reinsertion of the same mdg to the same place either in the presence or in absence of solo LTR sequence. Finally, the formation of deletions was observed. A 462-bp deletion destroying the white locus can be further repaired (w+ reversion). Thus, transposition bursts include many different genetic events. A novel system of prolonged genome destabilization was described. It depends on mobilization of a new mobile element called Stalker. After certain crosses Stalker actively moves for dozens of generations giving rise to large numbers of insertion mutations. Several novel genes were detected using mobilized Stalker. They include a modifier of mdg4 and six enhancers of yellow mutations.