RNA-binding proteins of the NXF (nuclear export factor) family and their connection with the cytoskeleton.

The mutual relationship between mRNA and the cytoskeleton can be seen from two points of view. On the one hand, the cytoskeleton is necessary for mRNA trafficking and anchoring to subcellular domains. On the other hand, cytoskeletal growth and rearrangement require the translation of mRNAs that are connected to the cytoskeleton. ß-actin mRNA localization may influence dynamic changes in the actin cytoskeleton. In the cytoplasm, long-lived mRNAs exist in the form of RNP (ribonucleoprotein) complexes, where they interact with RNA-binding proteins, including NXF (Nuclear eXport Factor). Dm NXF1 is an evolutionarily conserved protein in Drosophila melanogaster that has orthologs in different animals. The universal function of nxf1 genes is the nuclear export of different mRNAs in various organisms. In this mini-review, we briefly discuss the evidence demonstrating that Dm NXF1 fulfils not only universal but also specialized cytoplasmic functions. This protein is detected not only in the nucleus but also in the cytoplasm. It is a component of neuronal granules. Dm NXF1 marks nuclear division spindles during early embryogenesis and the dense body on one side of the elongated spermatid nuclei. The characteristic features of sbr mutants (sbr10 and sbr5 ) are impairment of chromosome segregation and spindle formation anomalies during female meiosis. sbr12 mutant sterile males with immobile spermatozoa exhibit disturbances in the axoneme, mitochondrial derivatives and cytokinesis. These data allow us to propose that the Dm NXF1 proteins transport certain mRNAs in neurites and interact with localized mRNAs that are necessary for dynamic changes of the cytoskeleton.

[Morphogenetic Networks which Determine the Spatial Expression of Zygotic Genes in Early Drosophila Embryo].

This review deals with the recent studies expanding the idea of positional information in the early embryogenesis of Drosophila melanogaster. Previous studies showed that, in the course of segment determination in Drosophila, information created by gradients of products of maternal coordinate genes is not "read" statically, being interpreted by their zygotic target genes via regulatory interactions. This leads to spatial shifts in the expression of target genes relative to the original positions as well as to dynamic reduction in the zygotic expression variability. However, according to recent data, interpretation of positional information includes the interaction between not only zygotic target genes but also the maternal coordinate genes themselves. Different systems of maternal coordinate genes (maternal systems)­the posterior-anterior, terminal, and dorsoventral­ can interact with each other. This is usually expressed in the regulation of zygotic target genes of one maternal system by other maternal systems. The concept of a "morphogenetic network" was introduced to define the interaction of maternal systems during determination of spatial gene expression in the early Drosophila embryo.

[THE ROLE OF sbr/Dm nxf1 GENE DURING SYNCYTIAL PERIODS OF DEVELOPMENT IN DROSOPHILA MELANOGASTER].

The syncytial development is a feature of early embryogenesis and spermatogenesis in Drosophila melanogaster. All elements of syncytium are interconnected by single cytoskeletal network that enables equal conditions and provides synchronic development. The cytoskeleton is essential for the formation and functioning of the mitotic spindle, cytoskeletal elements are the main structural component of cilia and flagella. Intra- and intercellular transport, morphogenesis processes depend from cytoskeleton on both within a single cell, and at the level of the whole organism. The sbr (small bristles) gene of D. melanogaster belongs to the NXF (nuclear export factor) evolutionarily conservative proteins family. Gene Dm nxf1 (sbr), as well as its orthologs in other organisms, controls the export of poly(A)-containing RNA from the nucleus to the cytoplasm, and the corresponding proteins are usually localized in the nucleus or in the nuclear envelope. For SBR protein we have shown the localization not only in the nucleus, but in the cytoplasm marking of characteristic cytoplasmic structures. A breach of the cytoskeleton in the sbr (Dm nxf1) mutant in D. melanogaster shown by us and cytoplasmic localization of the protein SBR allow us to link the specific functions of this protein with the dynamics of the cytoskeleton.

[Spermatogenesis in Drosophila melanogaster: the role of the basic transport receptor of the mRNA (Dm NXF1)].

Specificity of regulation of genes expression at the transcriptional and posttranscriptional levels is typical for spermatogenesis in Drosophila and mammals, including humans. It becomes apparent in the existence of testis specific NXF (nuclear export factor). We have shown that the Dm NXF1 (SBR) protein is present in considerable amounts at all stages of the spermatogenesis. Using the antibody for the C-terminal part of the Dm NXF1 protein we have shown the cytoplasmic localization of the Dm NXF1 protein at early stages of the spermatogenesis. This protein is localized in the nuclear envelope at the stage of rounded spermatid. During the period of elongation, the Dm NXF1 protein has a polar localization, and is located only along one side of the extended spermatid nucleus. At the stage of spermatid individualization, this protein in the form of large cytoplasmic granules moves to the tail of the spermatozoon.

[Centrosome as "a brain" of an animal cell].

Centrosomes are the major centre of microtubule nucleation and microtubule minus-ends concentration in animal cells. Microtubule plus-ends are directed to a nucleus and chromosomes or to a cell cortex. The crossing of signal transduction pathways and the network of interactions between signal molecules controlling cell cycle are revealed in centrosomes. The ability of centrosomes for reduplication suggests the existence of hypothetic template elements. It is attractive to suggest the essential role of specific centrosome-associated RNAs in biogenesis of centrosomes. Untranslated RNAs playing a structural role and mRNAs that are localized in centrosomes to regulate protein synthesis in close proximity to mitotic apparatus may be present among these RNAs. Centrosomes positioning plays the important role in determining of cell polarity. Centrosomes are critical for the formation and support of cilia and flagella having motility or sensory functions.

[Hyperthermia of male Drosophila melanogaster meiocytes induces abnormalities in both paternal and maternal sex chromosome sets of the offspring].

Nondisjunction and loss of sex chromosomes caused by exposure of male Drosophila melanogaster to heat shock (HS) (37 degrees C for 1 h) has been studied to determine the role of mutation l(1)ts403 (sbr10) in the control of chromosome segregation during cell division. Hyperthermia of males at the pupal stage has been demonstrated to increase the number of offspring with abnormalities of not only paternal, but also maternal sex chromosome sets. According to the criterion used, there is a temperature-sensitive period of spermatogenesis, which presumably coincides with meiosis. Phenotypes of some individuals correspond to the presence of two sex chromosomes of obtained from the same parent. The frequency of abnormal chromosome sets in the offspring of male carriers of the sbr10 mutation is about two times higher than in the offspring of males without this mutation.

[The relationship between nuclear-cytoplasmic transport and chromosome segregation].

Chromosomes/chromatids transport to cell division poles (chromosome segregation) and nuclear-cytoplasmic transport give way to each other during cell cycle. Disassembly and reassembly of the nuclear envelope during input or output mitosis are the critical time periods for changing one kind of transport system for the other one. The interest in the problem of relationships between nuclear-cytoplasmic transport and chromosome segregation came into view after revealing some factors involved in both transport systems. Among these factors are GTPase Ran, nuclear transport receptors and associated molecules, kinetochore proteins and proteins of nuclear pore complexes (nucleoprin, for example), spindle microtubules, microtubule motor proteins, and signal molecules. The role of all of these factors in the transport systems is not known. A decision of this problem will make it possible to determine mechanisms of both transport systems and to understand the character of evolutionary relationships between these systems.

[Genetic nature of abnormal larval development in the progeny of l(1)ts403(sbr10) females of Drosophila melanogaster].

In Drosophila melanogaster the small bristles (sbr) gene is vital and evolutionary conservative and controls nuclear export of mRNA. Sbr mutant alleles had a broad pleiotropic effect. High frequency of abnormal larva dying (up to 18 %) at the first instar stage in progeny of heat shock (37 degrees C, 1 h) treated mutant females is one of the most interesting l(l)ts403(sbr10) allele effects. Abnormal larvae display characteristic phenotype that involves the Malpighian tubules defect. Using interphase FISH method (fluorescence in situ hybridization), we showed that abnormal larvae had monosomy on chromosomes 2 and 3. DNA content in neuroblast interphase nuclei of abnormal larvae is 2.1 times less than in normal larvae. We suggest that abnormal larvae could be full or mosaic haploids that appeared as a result of maternal genome loss during fertilization or the mitotic division. Larvae with the same abnormalities appear in a progeny of females with different genotypes mating with males carrying compound chromosomes 2 or 3. FISH analysis showed that such larvae had monosomy only on a chromosome that is compound in paternal strain. Thus, monosomy on large autosomes may cause aspecial phenotype of abnormal larvae in D. melanogaster.

[Sterilizing effect of the mutant allele sbr10 (l(1)ts403) in compound with null alleles in Drosophila melanogaster females]. / Sterilizuiushchii éffekt mutantnogo allelia sbr10 (l(1)ts403) v kompaunde s nulevym allelem u samok Drosophila melanogaster.

In females of Df(1)v-L4/+(0/+) genotype, the presence of the wild-type allele of small bristles (sbr) gene in a single dose has no significant effect on their fecundity, whereas a reduced dose of the temperature-sensitive allele sbr10(l(1)ts403) causes a strong sterilizing effect in females Df(1)v-L4/sbr10 (0/sbr10) at permissive temperature. We studied the contribution to this effects of the following factors: resorption of egg chambers, decreased oviposition, offspring death at the embryonic and larval stages, and reduced fecundity in females 0/sbr10. Sterilizing effect of the mutant sbr10 allele proved to be primarily caused by offspring lethality at the embryonic and first-instar larval stages. In 0/+ females, the majority of undeveloped eggs contained embryos that perished at the late developmental stages, whereas in females 0/sbr10, at least 50% of undeveloped egg showed no visible signs of development or the embryo development was arrested at early stages of embryogenesis. The results obtained suggest insufficiency of the temperature-sensitive allele sbr10 in haploid state to ensure the reproductive functions of Drosophila melanogaster females.

[Genetic control of development of the Malpighian vessels in Drosophila melanogaster]. / Geneticheskii kontrol' razvitiia mal'pigievykh sosudov u Drosophila melanogaster.

Malpighian tubules of insects are a functional analog of mammalian kidneys and serve as a classical model for studying the structure and functions of transport epithelium. The review contains the data on structural organization, functioning, and formation of the Malpighian tubules during embryogenesis in Drosophila melanogaster. Various systems of genes are described that control the program of development of the renal (Malpighian) tubules in D. melanogaster. A special attention is paid to the ways of signal transduction and factors involved in cell differentiation, proliferation, and morphological transformation during development of the Malpighian tubules. Evolutionarily conservative genetic systems are considered that are involved in the control of development of both the renal epithelium of Drosophila and mammalian kidneys. A relationship was noted between the disturbed balance of genetic material and congenital defects of the human excretory system.

[Semidominant effect of the l(1)ts403 (sbr10) mutation on nondisjunction of sex chromosomes in meiosis in Drosophila melanogaster females exposed to heat]. / Poludominantnoe vliianie mutatsii l(1)ts403 (sbr10) na neraskhozhdenie polovykh khromosom v meioze u samok Drosophila melanogaster pri teplovom vozdeistvii.

The sbr gene of Drosophila melanogaster belongs to the NXF (nuclear export factor) family responsible for the mRNA transport from nucleus to cytoplasm. We have shown that in the heat-exposed (37 degrees C, 1 h) females, the l(1)ts403 (sbr10) mutation leads, in particular, to the high-frequency nondisjunction and loss of sex chromosomes in meiosis. For this trait, the incomplete dominance of the sbr10 mutation is observed. At the same time, the sbr10 mutation is recessive for many other traits of the heat-exposed flies: reduced viability, low fertility, impaired synthesis of the heat shock proteins, etc. The females heterozygous for the null allele (Df(1)vL4, a deletion eliminating gene srb) do not differ from females homozygous for the wild-type allele in frequency of the heat shock-induced nondisjunction and loss of sex chromosomes in meiosis. Because of this, the sbr10 mutation can be assigned to the gain-of-function alleles (those gaining the dominance function). Expression of the mutant sbr10 allele against the background of the wild-type allele suggests that in the heat shock-exposed females, the heat-modified product of this ts allele has a strong effect on sex chromosome disjunction in meiosis.

[The sbr gene product in Drosophila melanogaster and its orthologs in yeast (Mex67p) and human (TAP)]. / Produkty gena sbr u Drosophila melanogaster i ego ortologi u drozhzhei (Mex67p) i cheloveka (TAP).

A DNA sequence from the 9F region of Drosophila melanogaster polytene chromosomes was cloned. Sequencing the cloned region and its comparison with the known sequences of the D. melanogaster genome showed that the cloned DNA part contains gene sbr and adjacent sequences. The literature data on the structure and functions of genes TAP in humans and Mex67 in yeast are discussed. These genes are orthologous to the sbr gene of Drosophila and control mRNA export from the nucleus to the cytoplasm. The literature evidence is consistent with the recessive expression of mutation l(1)ts403 (sbr10) upon heat treatment that is manifested as impaired HSP synthesis at the posttranscriptional level. However, it fails to explain the semidominant effect of the mutation manifested in high frequency of meiotic sex-chromosome nondisjunction in heat-treated females. A comparison of amino-acid sequences corresponding to the products of the three orthologous genes, TAP, Mex67, and sbr, showed that the sbr gene product of Drosophila is more similar to the human TAP factor than to the Mex67 factor in yeast.

[Maternal and paternal effects on the specific mutation l(1)ts403 of thermosensitivity of early Drosophila melanogaster embryos]. / Vliianie materinskogo i otsovskogo organizmov na opredeliaemuiu mutatsiei l(1)ts403 teplochuvstvitel'nost' rannykh émbrionov Drosophila melanogaster.

High thermosensitivity of early embryos controlled by mutation l(1)ts403 with disturbed heat-shock response was studied. Thermosensitivity was examined in early (0-1 h) and late (3.5-4.5 h) embryos obtained by reciprocal crosses and backcrosses. It was shown that mutation l(1)ts403 lacks maternal effect. In progeny of reciprocal crosses, early embryonic thermosensitivity was intermediate with regard to that of progeny obtained by interlinear crosses. In early embryos of Drosophila, zygotic genes are not expressed and synthesis heat-shock protein synthesis is not induced. Based on this, it was proposed that the product of gene l(1)ts403, which affects early embryonic thermosensitivity, is transmitted both paternally and maternally and shows dosage effect.

[Development of thermotolerance in Drosophila melanogaster line l(1) ts403 with a defect in heat shock protein synthesis]. / Formirovanie termotolerantnosti u linii Drosophila melanogaster l(1) ts403 s narushennym sintezom belkov teplovogo shoka.

To elucidate the role of heat shock proteins (HSP) in the formation of resistance to extreme factors and in the development of organismic and cell response to these factors, thermotolerance in a Drosophila melanogaster line with defective HSP synthesis was studied with regard to several criteria: (1) survival of adult-females; (2) damage to egg chambers in ovarioles; (3) dynamics of oviposition; (4) frequency of loss and nondisjunction of sex chromosomes in meiosis of females exposed to a heat shock (HS). According to all these criteria, the l(l)ts403 females were more sensitive to a HS 37 degrees C, the exposure at 37 degrees C for 1 h (HS37) than the females of the wild-type line Canton S. Only the data on the first three aforementioned parameters were indicative of thermotolerance development. In files exposed to HS35 followed by HS37, a decrease in nondisjunction and loss of sex chromosomes in the 3- and 4-day ovipositions was observed as compared to the flies exposed to HS37 only. This can be explained by the differences in oviposition dynamics and, consequently, in the realization rate of the oogenesis stages in these two experimental variants. The pleiotropic effect of the l(l)ts403 mutation that led to a disturbance in HSP gene expression at the posttranscriptional level and to an increase in the frequency of sex chromosome nondisjunction in the meiosis of females exposed to HS37 suggests that these processes were connected. As no thermotolerance was revealed by studying the sex chromosome nondisjunction, but thermotolerance was found by estimating the other parameters, we suggest that the product of the gene studied is involved in a signal system operating at a stage that precedes the HS-induced changes in the translation and division apparatuses of a cell.

[Consequences of exposure to extreme conditions in somatic cells of Drosophila melanogaster under conditions of disturbed synthesis of heat shock proteins]. / Posledstviia ékstremal'nykh vozdeistvii na somaticheskie kletki Drosophila melanogaster v usloviiakh narushennogo sinteza belkov teplovogo shoka.

Restoration of cell proliferation and repair of chromosome damage (chromatin agglutination, pulverization, or aggregation) in conditions of disturbed synthesis of heat shock proteins (HSPs) was studied in nerve ganglia of Drosophila melanogaster larvae. Two approaches were used to suppress the heat shock response: (1) anaerobic heating of wild-type Canton S larvae at 37 degrees C for 13 min, which temporarily blocked HSP gene expression at the transcriptional level [1], and (2) aerobic heating of mutant l(1)ts403 larvae at 37 degrees C for 30 min, which disturbed HSP gene expression at the posttranscriptional level [2]. The duration of heat treatment was selected according to the period of regression of heat shock puffs [3]. In both experimental systems, the period of HSP synthesis and the delay in resuming cell proliferation and recovering from mitotic chromosome stickiness increased similarly, compared to corresponding positive control. This suggests the involvement of HSPs in repairing chromatin protein damage leading to chromosome stickiness and in resuming cell proliferation. An increase in the number of cells with morphologically abnormal (pulverized or aggregated) chromatin was observed only after heat treatment for 30 min (rather than for 13 min). However, the patterns of changes in the number of such cells in Canton S and l(1)ts403 larvae recovering from 30-min heat treatment differed from one another. Different mechanisms responsible for induction of chromosome abnormalities (premature condensation of interphase chromosomes or disturbed condensation of mitotic chromosomes) and different roles of HSP in these processes are discussed.

[The regression time of heat-shock puffs in the polytene chromosomes of Drosophila melanogaster as a criterion for assessing the effect of different stress exposures]. / Vremia regressii puffov teplovogo shoka v politennykh khromosomakh drozofily Drosophila melanogaster kak kriterii dlia ostenki éffekta razlichnykh stressovykh vozdeistvii.

The time of regression of heat shock puffs was studied in the polytene chromosomes of Drosophila melanogaster larvae of mutant stock (1(1)ts403, defective in heat shock protein (HSP) system, and of the wild type stock Canton S after heat shock (37 degrees C), after placing of larvae to anaerobic conditions (dipping into physiological solution), and after combination of these treatments. It is shown that the time of regression of heat shock puffs depends on the specificity of the treatment (heat shock or anaerobic conditions), its duration (13 or 30 min), or on the peculiarity of functioning of HSP system in the cells of different stock larvae. Our results are in accordance with the idea of the HSP genes expression autoregulation, and allow to use the heat shock puff regression time as a criterion for estimation of damaging effects of stress factors.

[Mechanisms ensuring the resistance of the genetic material of the cell to stress exposures]. / Mekhanizmy, obespechivaiushchie ustoichivost' geneticheskogo materiala kletki k stressovym vozdeistviiam.

A brief review of studies performed in the Department of Genetics of St. Petersburg University by M.E. Lobashev and his disciples is presented. The results of these studies prove that the formation of a mutation is a multistage process involving many cell and organism systems (including repair systems, systems that determine sexual dimorphism, etc.), which are affected by environmental factors (e.g., extreme temperatures). They can hinder or accelerate the mutational process, in this way providing both a superadditive effect and adaptive response. Recent studies deal with a universal system of heat shock proteins, which is involved in the maintenance of resistance of genetic material and genetic processes in the cell.

[Role of heat-shock proteins in recovery of cell proliferation following high temperature treatment of Drosophila melanogaster larvae]. / Rol' belkov teplovogo shoka v vosstanovlenii kletochnoi proliferatsii posle vozdeistviia vysokoi temperaturoi na lichinok Drosophila melanogaster.

The processes of the recovery of proliferation activity of nervous ganglion cells following heat-shock (37 degrees C, 30 min) were compared in two strains of Drosophila melanogaster (Canton S--the wild-type strain and 1(1)ts403--the mutant with the defect in the heat-shock protein system). The ts-mutant is characterized by the delay n reaching the maximum level in the HSP's synthesis and by more prolonged synthesis of these proteins after heat shock as compared with the wild-type strain. The block in cell proliferation after heat-shock is also more prolonged in the ts mutant's nervous ganglion in comparison with the wild-type strain. These results are n accordance with the hypothesis about the role of HSP's in cell proliferation.

[Role of heat-shock proteins in the recovery of mitotic chromosome damage induced by high temperature in Drosophila melanogaster]. / Rol' belkov teplovogo shoka v vosstanovlenii industirovannykh vysokoi temperaturoi povrezhdenii mitoticheskikh khromosom u Drosophila melanogaster.

The synthesis of the heat-shock proteins (HSP) and the frequency of the mitotic chromosome damages (pulverizations, chromosome, chromatid stickiness, etc.) was studied in the cells of larva nervous ganglion in the process of recovery after heat shock (37 degrees C, 30 min). Analysis was performed in two strains of Drosophila melanogaster (Canton S-the wild type and the mutant l(1)ts403 with the defect in the HSP system). Correlation between the dynamics of HSP synthesis and the alteration of the chromosome pulverization and stickiness frequency was shown for both Drosophila strains under study. These results, in accord with the data on HSPs' binding to chromosomes following heat shock and their role as molecular chaperones, allowed to suggest that HSPs took part in chromosome condensation and in the recovery of heat shock induced damages leading to chromosome and chromatid stickiness.

[Temperature modification of the mutation process and heat shock proteins]. / Temperaturnaia modifikatsiia mutatsionnogo protsessa i belki teplovogo shoka.

Heat shock protein synthesis and mutagenesis (X-chromosome losses induced by radiation and high temperature) were studied in different. Drosophila melanogaster strains. Two models (strain l(1)ts403 with the defect in heat shock protein synthesis and the heat-resistant T strain with a specific reaction to the extreme temperature differing from the wild type strains) were used. The correlation between heat shock protein synthesis and the effect of synergism in the action of radiation and heat shock was revealed. It was concluded that HSPs are one of the components in mutagenic processes.