Alsu Saifitdinova

[NSI+]: a novel non-Mendelian nonsense suppressor determinant in Saccharomyces cerevisiae

Non-Mendelian determinants that control heritable traits in yeast are subdivided into two major groups—one that includes DNA- or RNA-based elements and another that comprises protein-based factors that are analogous to mammalian prion. All yeast non-Mendelian determinants show dominant inheritance, and some of them demonstrate cytoplasmic infectivity. Only prions, however, harbor-specific features, such as high frequency of induction following overproduction of prion-encoding protein, loss of the protein’s normal function, and reversible curability. Here, we describe a novel nonchromosomal determinant that, in addition to [PSI+] and [ISP+], is involved in epigenetic control of nonsense suppression. This determinant, which we have designated [NSI+], causes nonsense suppression in the strains bearing the N-terminal-deleted or -modified SUP35 gene, but has no manifestation in the strains with the intact copy of SUP35. [NSI+] shows dominant non-Mendelian inheritance, reversible curability and may be transmitted by cytoduction, albeit with low frequency. Similar to yeast prions, this determinant can be cured by deletion or mutational inactivation of Hsp104. We have shown that [NSI+] does not correspond to the already identified yeast prions. Based on the data obtained, we hypothesize that [NSI+] is a novel prion factor involved in epigenetic control of nonsense suppression.

Lampbrush chromosomes of the chaffinch (Fringilla coelebs L.).

The seven macrochromosomes of the chaffinch (Fringilla coelebs L.) are described in their lampbrush form. The relative lengths of bivalents, the positions and arrangements of chromosomal regions with lateral loops of similar length and appearance, as well as the positions of protein bodies and loops of peculiar morphology have been defined and mapped, so that each of the seven lampbrush macrobivalents may be identified in oocytes from every individual of the species. This morphological analysis has been supplemented by determining the positions of certain loci and objects that are specifically and consistently labelled after immunostaining or fluorescence in-situ hybridization with defined molecular probes.

Homoploid hybrid speciation and genome evolution via chromosome sorting

Genomes of numerous diploid plant and animal species possess traces of interspecific crosses, and many researches consider them as support for homoploid hybrid speciation (HHS), a process by which a new reproductively isolated species arises through hybridization and combination of parts of the parental genomes, but without an increase in ploidy. However, convincing evidence for a creative role of hybridization in the origin of reproductive isolation between hybrid and parental forms is extremely limited. Here, through studying Agrodiaetus butterflies, we provide proof of a previously unknown mode of HHS based on the formation of post-zygotic reproductive isolation via hybridization of chromosomally divergent parental species and subsequent fixation of a novel combination of chromosome fusions/fissions in hybrid descendants. We show that meiotic segregation, operating in the hybrid lineage, resulted in the formation of a new diploid genome, drastically rearranged in terms of chromosome number. We also demonstrate that during the heterozygous stage of the hybrid species formation, recombination was limited between rearranged chromosomes of different parental origin, representing evidence that the reproductive isolation was a direct consequence of hybridization.

Identification of genes encoding potentially amyloidogenic proteins that take part in the regulation of nonsense suppression in yeast Saccharomyces cerevisiae

Previously, we demonstrated that SUP35 N-terminal deletion creates a specific genetic back-ground permitting the identification of novel genes and epigenetic determinants controlling nonsense suppression. In the present study, using a genomic screen, we found three genes encoding potentially amyloidogenic proteins, whose overexpression affects nonsense suppression in the strain producing chimeric Aβ-Sup35MC protein on the background of SUP35 deletion encoding releasing factor eRF3. These genes, NAB2, NAB3, and VTS1, were found to participate in the regulation of nonsense suppression in yeast S. cerevisiae.

Yeast chaperone Hsp104 controls gene expression at the posttranscriptional level

Yeast chaperone Hsp104 is known as a protein responsible for dissociation of aggregates of heat-damaged proteins and prion aggregates into smaller pieces or monomers. The effects of Hsp104 on PrP-GFP and GFP were analyzed. PrP-GFP forms high-molecular-weight aggregates, whereas GFP is unable to aggregate in yeast cells. Hsp104 proved to regulate the amount of PrP-GFP and GFP in yeast cells, and the direction of chaperone action depended on the promoters controlling the production of these proteins. Overproduction of Hsp104 increased the levels of PrP-GFP and GFP when their genes were controlled by the CUP1 promoter. In contrast, overproduction of Hsp104 decreased the levels of PrP-GFP and GFP in the case of their expression under the control of the GPD promoter. The effects of Hsp104 were not related to any changes in the contents of mRNAs of the genes under investigation nor to the ability of the proteins to form aggregates. Thus, the Hsp104 functions were not confined to dissociation of protein aggregates. Hsp104 was assumed to regulate gene expression at the posttranscriptional level.

Cytological maps of lampbrush chromosomes of European water frogs (Pelophylax esculentus complex) from the Eastern Ukraine

BackgroundHybridogenesis (hemiclonal inheritance) is a kind of clonal reproduction in which hybrids between parental species are reproduced by crossing with one of the parental species. European water frogs (Pelophylax esculentus complex) represent an appropriate model for studying interspecies hybridization, processes of hemiclonal inheritance and polyploidization. P. esculentus complex consists of two parental species, P. ridibundus (the lake frog) and P. lessonae (the pool frog), and their hybridogenetic hybrid – P. esculentus (the edible frog). Parental and hybrid frogs can reproduce syntopically and form hemiclonal population systems. For studying mechanisms underlying the maintenance of water frog population systems it is required to characterize the karyotypes transmitted in gametes of parental and different hybrid animals of both sexes.ResultsIn order to obtain an instrument for characterization of oocyte karyotypes in hybrid female frogs, we constructed cytological maps of lampbrush chromosomes from oocytes of both parental species originating in Eastern Ukraine. We further identified certain molecular components of chromosomal marker structures and mapped coilin-rich spheres and granules, chromosome associated nucleoli and special loops accumulating splicing factors. We recorded the dissimilarities between P. ridibundus and P. lessonae lampbrush chromosomes in the length of orthologous chromosomes, number and location of marker structures and interstitial (TTAGGG)n-repeat sites as well as activity of nucleolus organizer. Satellite repeat RrS1 was mapped in centromere regions of lampbrush chromosomes of the both species. Additionally, we discovered transcripts of RrS1 repeat in oocytes of P. ridibundus and P. lessonae. Moreover, G-rich transcripts of telomere repeat were revealed in association with terminal regions of P. ridibundus and P. lessonae lampbrush chromosomes.ConclusionsThe constructed cytological maps of lampbrush chromosomes of P. ridibundus and P. lessonae provide basis to define the type of genome transmitted within individual oocytes of P. esculentus females with different ploidy and from various population systems.

Precise identification of chicken chromosomes in the lampbrush form using chromosome painting probes

Chromosome painting probes specific for macrochromosomes 1, 2, 3, 4, 5, and Z were applied to both mitotic and lampbrush chromosomes of the chicken (Gallus gallus domesticus). Five autosomal macrobivalents and sex chromosome Z in the lampbrush phase were identified and their correspondence to the target chromosomes in the metaphase of mitosis was shown. Nascent transcripts on lateral loops of the target lampbrush chromosome were intensively labelled when the hybridization was performed without RNase A treatment according to the DNA/(DNA+RNA) hybridization protocol.

Optional Endoreplication and Selective Elimination of Parental Genomes during Oogenesis in Diploid and Triploid Hybrid European Water Frogs.

Incompatibilities between parental genomes decrease viability of interspecific hybrids; however, deviations from canonical gametogenesis such as genome endoreplication and elimination can rescue hybrid organisms. To evaluate frequency and regularity of genome elimination and endoreplication during gametogenesis in hybrid animals with different ploidy, we examined genome composition in oocytes of di- and triploid hybrid frogs of the Pelophylax esculentus complex. Obtained results allowed us to suggest that during oogenesis the endoreplication involves all genomes occurring before the selective genome elimination. We accepted the hypothesis that only elimination of one copied genome occurs premeiotically in most of triploid hybrid females. At the same time, we rejected the hypothesis stating that the genome of parental species hybrid frogs co-exist with is always eliminated during oogenesis in diploid hybrids. Diploid hybrid frogs demonstrate an enlarged frequency of deviations in oogenesis comparatively to triploid hybrids. Typical for hybrid frogs deviations in gametogenesis increase variability of produced gametes and provide a mechanism for appearance of different forms of hybrids.

Chicken rRNA Gene Cluster Structure

Ribosomal RNA (rRNA) genes, whose activity results in nucleolus formation, constitute an extremely important part of genome. Despite the extensive exploration into avian genomes, no complete description of avian rRNA gene primary structure has been offered so far. We publish a complete chicken rRNA gene cluster sequence here, including 5’ETS (1836 bp), 18S rRNA gene (1823 bp), ITS1 (2530 bp), 5.8S rRNA gene (157 bp), ITS2 (733 bp), 28S rRNA gene (4441 bp) and 3’ETS (343 bp). The rRNA gene cluster sequence of 11863 bp was assembled from raw reads and deposited to GenBank under KT445934 accession number. The assembly was validated through in situ fluorescent hybridization analysis on chicken metaphase chromosomes using computed and synthesized specific probes, as well as through the reference assembly against de novo assembled rRNA gene cluster sequence using sequenced fragments of BAC-clone containing chicken NOR (nucleolus organizer region). The results have confirmed the chicken rRNA gene cluster validity.

Karyosystematics and molecular taxonomy of the anomalous blue butterflies (Lepidoptera, Lycaenidae) from the Balkan Peninsula.

Abstract The Balkan Peninsula represents one of the hottest biodiversity spots in Europe. However, the invertebrate fauna of this region is still insufficiently investigated, even in respect of such well-studied organisms as Lepidoptera. Here we use a combination of chromosomal, molecular and morphological markers to rearrange the group of so-called anomalous blue butterflies (also known as ‘brown complex’ of the subgenus Agrodiaetus Hübner, [1822] and as the Polyommatus (Agrodiaetus) admetus (Esper, 1783) species group) and to reveal its cryptic taxonomic structure. We demonstrate that Polyommatus aroaniensis (Brown, 1976) is not as widespread in the Balkans as was previously thought. In fact, it has a dot-like distribution range restricted to the Peloponnese Peninsula in South Greece. Polyommatus orphicus Kolev, 2005 is not as closely related to the Turkish species Polyommatus dantchenkoi (Lukhtanov & Wiemers, 2003) as was supposed earlier. Instead, it is a Balkan endemic represented by two subspecies: Polyommatus orphicus orphicus (Bulgaria) and Polyommatus orphicus eleniae Coutsis & De Prins, 2005 (Northern Greece). Polyommatus ripartii (Freyer, 1830) is represented in the Balkans by an endemic subspecies Polyommatus ripartii pelopi. The traditionally recognized Polyommatus admetus (Esper, 1783) is shown to be a heterogeneous complex and is divided into Polyommatus admetus sensu stricto (the Balkans and west Turkey) and Polyommatus yeranyani (Dantchenko & Lukhtanov, 2005) (east Turkey, Armenia, Azerbaijan and Iran). Polyommatus nephohiptamenos (Brown & Coutsis, 1978) is confirmed to be a species with a dot-like distribution range in Northern Greece. Finally, from Central Greece (Timfristos and Parnassos mountains) we describe Polyommatus timfristos Lukhtanov, Vishnevskaya & Shapoval, sp. n. which differs by its haploid chromosome number (n=38) from the closely related and morphologically similar Polyommatus aroaniensis (n=47-48) and Polyommatus orphicus (n=41-42). We provide chromosomal evidence for three separate south Balkan Pleistocene refugia (Peloponnesse, Central Greece and Northern Greece/South Bulgaria) and stress the biogeographic importance of Central Greece as a place of diversification. Then we argue that the data obtained have direct implications for butterfly karyology, taxonomy, biogeography and conservation.