Lev G. Nikolaev

D.Sc (biological sciences)

Leading research fellow (Laboratory of human genes structure and functions)

Phone: +7 (495) 3307029

E-mail: lev@ibch.ru

Selected publications

  1. Bulanenkova S.S., Kozlova A.A., Kotova E.S., Snezhkov E.V., Azhikina T.L., Akopov S.B., Nikolaev L.G., Sverdlov E.D. (2011). Dam methylase accessibility as an instrument for analysis of mammalian chromatin structure. Epigenetics 6 (9), 1078–1084 [+]

    For a 140 kb human genome locus, an analysis of the distribution of Dam methylase accessible sites, DNase I sensitive and resistant regions, unmethylated CpG sites and acetylated histone H3 molecules was performed and compared with transcriptional activity of the genes within the locus. A direct correlation was found between the extent of Dam methylation and C5 cytosine (CpG) methylation. It was also demonstrated that promoter regions of all highly and moderately transcribed genes are highly accessible to methylation by Dam methylase. In contrast, promoters of non transcribed genes showed a very low extent of Dam methylation. Promoter regions of non transcribed genes were also highly CpG methylated, and the promoter and more distant 5'-regions of the housekeeping gene COX6B1 were substantially CpG demethylated. Some highly Dam methylase accessible regions are present in the intergenic regions of the locus suggesting that the latter contain either unidentified non-coding transcripts or extended regulatory elements like locus control regions.

  2. Didych D.A., Smirnov N.A., Kotova E.S., Akopov S.B., Nikolaev L.G., Sverdlov E.D. (2011). Functional dissection of an enhancer-like element located within the second intron of the human U2AF1L4 gene. Biochemistry Mosc. 76 (8), 951–7 [+]

    A detailed functional and evolutionary analysis of an enhancer element of the human genome (enhancer 12) located in the second intron of the U2AF1L4 gene, which we identified earlier, is presented. Overlapping fragments of the studied genome region were analyzed for enhancer activity, and the site responsible for the activity of this element was identified using transient transfections of HeLa cells. Comparison of the enhancer 12 sequence with orthologous sequences from seven primate species revealed the existence of evolutionarily conserved sequences within this element. One of the identified conservative regions is likely responsible for the enhancer activity and is able to specifically interact in vitro with proteins of HeLa cell nuclear extract. The ability of orthologous primate sequences to compete with enhancer 12 for binding with HeLa cell nuclear extract proteins and to enhance the activity of the reporter gene in transient transfection of HeLa cells is demonstrated.

  3. Nikolaev L.G., Akopov S.B., Didych D.A., Sverdlov E.D. (2009). Vertebrate Protein CTCF and its Multiple Roles in a Large-Scale Regulation of Genome Activity. Curr. Genomics 10 (5), 294–302 [+]

    The CTCF transcription factor is an 11 zinc fingers multifunctional protein that uses different zinc finger combinations to recognize and bind different sites within DNA. CTCF is thought to participate in various gene regulatory networks including transcription activation and repression, formation of independently functioning chromatin domains and regulation of imprinting. Sequencing of human and other genomes opened up a possibility to ascertain the genomic distribution of CTCF binding sites and to identify CTCF-dependent cis-regulatory elements, including insulators. In the review, we summarized recent data on genomic distribution of CTCF binding sites in the human and other genomes within a framework of the loop domain hypothesis of large-scale regulation of the genome activity. We also tried to formulate possible lines of studies on a variety of CTCF functions which probably depend on its ability to specifically bind DNA, interact with other proteins and form di- and multimers. These three fundamental properties allow CTCF to serve as a transcription factor, an insulator and a constitutive dispersed genome-wide demarcation tool able to recruit various factors that emerge in response to diverse external and internal signals, and thus to exert its signal-specific function(s).

  4. Chernov I.P., Timchenko K.A., Akopov S.B., Nikolaev L.G., Sverdlov E.D. (2007). Identification of tissue-specific DNA-protein binding sites by means of two-dimensional electrophoretic mobility shift assay display. Anal. Biochem. 364 (1), 60–6 [+]

    We developed a technique of differential electrophoretic mobility shift assay (EMSA) display allowing identification of tissue-specific protein-binding sites within long genomic sequences. Using this approach, we identified 10 cell type-specific protein-binding sites (protein target sites [PTSs]) within a 137-kb human chromosome 19 region. In general, tissue-specific binding of proteins from different nuclear extracts by individual PTSs did not follow the all-or-nothing principle. Most often, PTS-protein complexes were formed in all cases, but they were different for different nuclear extracts used.

  5. Bulanenkova S., Snezhkov E., Nikolaev L., Sverdlov E. (2007). Identification and mapping of open chromatin regions within a 140 kb polygenic locus of human chromosome 19 using E. coli Dam methylase. Genetica 130 (1), 83–92 [+]

    Using transient expression of the E. coli Dam methylase gene and analysis of the distribution of methylated GATC sites, we studied the distribution of open chromatin regions within a 140 kb long human genome segment in HEK-293 cells. Dam methylated sites were found in gene introns, exons, and intergenic regions, and their distribution along DNA was uneven. There were regions of high and low density of Dam methylated GATC sites, presumably corresponding to "open" and "closed" chromatin regions, respectively, and to the functional profile of the genomic locus under study. The Dam methylation profile was also generally in agreement with transcriptional activity of genes in the locus. Moreover, DNA regions accessible to Dam methylase apparently coincided with those hypersensitive to DNase I.

  6. Shaposhnikov S.A., Akopov S.B., Chernov I.P., Thomsen P.D., Joergensen C., Collins A.R., Frengen E., Nikolaev L.G. (2007). A map of nuclear matrix attachment regions within the breast cancer loss-of-heterozygosity region on human chromosome 16q22.1. Genomics 89 (3), 354–61 [+]

    There is abundant evidence that the DNA in eukaryotic cells is organized into loop domains that represent basic structural and functional units of chromatin packaging. To explore the DNA domain organization of the breast cancer loss-of-heterozygosity region on human chromosome 16q22.1, we have identified a significant portion of the scaffold/matrix attachment regions (S/MARs) within this region. Forty independent putative S/MAR elements were assigned within the 16q22.1 locus. More than 90% of these S/MARs are AT rich, with GC contents as low as 27% in 2 cases. Thirty-nine (98%) of the S/MARs are located within genes and 36 (90%) in gene introns, of which 15 are in first introns of different genes. The clear tendency of S/MARs from this region to be located within the introns suggests their regulatory role. The S/MAR resource constructed may contribute to an understanding of how the genes in the region are regulated and of how the structural architecture and functional organization of the DNA are related.

  7. Akopov S.B., Ruda V.M., Batrak V.V., Vetchinova A.S., Chernov I.P., Nikolaev L.G., Bode J., Sverdlov E.D. (2006). Identification, genome mapping, and CTCF binding of potential insulators within the FXYD5-COX7A1 locus of human chromosome 19q13.12. Mamm. Genome 17 (10), 1042–9 [+]

    Identification of insulators is one of the most difficult problems in functional mapping of genomes. For this reason, up to now only a few insulators have been described. In this article we suggest an approach that allows direct isolation of insulators by a simple positive-negative selection based on blocking enhancer effects by insulators. The approach allows selection of fragments capable of blocking enhancers from mixtures of genomic fragments prepared from up to 1-Mb genomic regions. Using this approach, a 1-Mb human genome locus was analyzed and eight potential insulators were selected. Five of the eight sequences were positioned in intergenic regions and two were within introns. The genes of the alpha-polypeptide H+/K+ exchanging ATPase (ATP4A) and amyloid beta (A4) precursor-like protein 1 (APLP1) within the locus studied were found to be flanked by insulators on both sides. Both genes are characterized by distinct tissue-specific expression that differs from the tissue specificity of the surrounding genes. The data obtained are consistent with the conception that insulators subdivide genomic DNA into loop domains that comprise genes characterized by similar expression profiles. Using chromatin immunoprecipitation assay, we demonstrated also that at least six of the putative insulators revealed in this work could bind the CTCF transcription factor in vivo. We believe that the proposed approach could be a useful instrument for functional analysis of genomes.

  8. Vetchinova A.S., Akopov S.B., Chernov I.P., Nikolaev L.G., Sverdlov E.D. (2006). Two-dimensional electrophoretic mobility shift assay: identification and mapping of transcription factor CTCF target sequences within an FXYD5-COX7A1 region of human chromosome 19. Anal. Biochem. 354 (1), 85–93 [+]

    An approach for fast identification and mapping of transcription factor binding sites within long genomic sequences is proposed. Using this approach, 10 CCCTC-binding factor (CTCF) binding sites were identified within a 1-Mb FXYD5-COX7A1 human chromosome 19 region. In vivo binding of CTCF to these sites was verified by chromatin immunoprecipitation assay. CTCF binding sites were mapped within gene introns and intergenic regions, and some of them contained Alu-like repeated elements.

  9. Chernov I.P., Akopov S.B., Nikolaev L.G., Sverdlov E.D. (2006). Identification and mapping of DNA binding proteins target sequences in long genomic regions by two-dimensional EMSA. BioTechniques 41 (1), 91–6 [+]

    Specific binding of nuclear proteins, in particular transcription factors, to target DNA sequences is a major mechanism of genome functioning and gene expression regulation in eukaryotes. Therefore, identification and mapping specific protein target sites (PTS) is necessary for understanding genomic regulation. Here we used a novel two-dimensional electrophoretic mobility shift assay (2D-EMSA) procedure for identification and mapping of 52 PTS within a 563-kb human genome region located between the FXYD5 and TZFP genes. The PTS occurred with approximately equal frequency within unique and repetitive genomic regions. PTS belonging to unique sequences tended to group together within gene introns and close to their 5' and 3' ends, whereas PTS located within repeats were evenly distributed between transcribed and intragenic regions.