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.

[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.

[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.

[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.