a b s t r a c t RNA-dependent DNA methylation (RdDM) is an important regulatory event involved in... more a b s t r a c t RNA-dependent DNA methylation (RdDM) is an important regulatory event involved in repressive epigenetic modifications that can trigger transcriptional gene silencing (TGS). The criteria we used to pick out promoter sequences targeted by RdDM in Arabidopsis thaliana were the main RdDM hallmark properties: 24nt siRNAs as inducers of DNA methylation and transposable elements (TE) as one of the major targets of RdDM. Those genes whose promoters comprised overlapping sites for 24nt siRNA hits, TE and DNA methylation (siRNA/TE/Methylation overlapping regions), were defined as candidates that might be silenced by RdDM. On this basis two gene sets were created which include abiotic and biotic stress-responsive genes whose promoters may be silenced by RdDM. The DNA methylation status of the At3g50770 (CML41) promoter e one of the selected candidates, was experimentally assayed, and it showed dependence on the RdDM-associated Polymerase IV and Polymerase V. A publicly available 24nt siRNA-centered database called starPRO was developed that allows users easily to discover whether a particular promoter sequence is related to RdDM-associated features such as 24nt siRNA-target sites, TE, tandem repeats and DNA methylation.
Background: MicroRNAs (miRNAs) are one of the most abundant groups of regulatory genes in multice... more Background: MicroRNAs (miRNAs) are one of the most abundant groups of regulatory genes in multicellular organisms, playing important roles in many fundamental cellular processes. More than four hundred miRNAs have been identified in humans and the deregulation of miRNA expression has been also shown in many cancers. Despite the postulated involvement of miRNAs in tumourigenesis, there are only a few examples where an oncogene or a tumour suppressor has been identified as a miRNA target.
Computational Biology and Chemistry / Computers & Chemistry, 2009
MicroRNAs are important negative regulators of gene expression in higher eukaryotes. The miRNA re... more MicroRNAs are important negative regulators of gene expression in higher eukaryotes. The miRNA repertoire of the closest human animal relative, the chimpanzee (Pan troglodytes), is largely unknown. In this study, we focused on computational search of novel miRNA homologs in chimpanzee. We have searched and analyzed the chimp homologs of the human pre-miRNA and mature miRNA sequences. Based on a homology search of the chimpanzee genome with human miRNA precursor sequences as queries, we identified 639 chimp miRNA genes, including 529 novel chimp miRNAs. 91.8% of chimp mature miRNAs and 60.3% of precursors are 100% identical to their human orthologs. The pre-miRNA secondary structures, miRNA families, and clusters are also highly conserved. We also found certain sequence differences in pre-miRNAs and even mature miRNAs that occurred after the divergence of the two species. Some of these differences (especially in mature miRNAs) could have caused species-specific changes in the expression levels of their target genes which in turn could have resulted in phenotypic variation between human and chimp.
Regulation of post-transcriptional gene expression by microRNAs (miRNA) has so far been validated... more Regulation of post-transcriptional gene expression by microRNAs (miRNA) has so far been validated for only a few mRNA targets. Based on the large number of miRNA genes and the possibility that one miRNA might influence gene expression of several targets simultaneously, the quantity of ribo-regulated genes is expected to be much higher. Here, we describe the web tool MicroInspector that will analyse a userdefined RNA sequence, which is typically an mRNA or a part of an mRNA, for the occurrence of binding sites for known and registered miRNAs. The program allows variation of temperature, the setting of energy values as well as the selection of different miRNA databases to identify miRNA-binding sites of different strength. MicroInspector could spot the correct sites for miRNA-interaction in known target mRNAs. Using other mRNAs, for which such an interaction has not yet been described, we discovered frequently potential miRNA binding sites of similar quality, which can now be analysed experimentally. The MicroInspector program is easy to use and does not require specific computer skills. The service can be accessed via the MicroInspector web server at http://www.imbb. forth.gr/microinspector.
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Papers by Vesselin Baev