Kovalchuk, Igor

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https://opus.uleth.ca/handle/10133/3488

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Browsing Kovalchuk, Igor by Author "Byeon, Boseon"

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    Genomic and epigenomic changes in the progeny of cold-stressed Arabidopsis thaliana plants
    (MDPI, 2024) Rahman, Ashif; Yadav, Narendra Singh; Byeon, Boseon; Ilnytskyy, Yaroslav; Kovalchuk, Igor
    Plants are continuously exposed to various environmental stresses. Because they can not escape stress, they have to develop mechanisms of remembering stress exposures somatically and passing it to the progeny. We studied the Arabidopsis thaliana ecotype Columbia plants exposed to cold stress for 25 continuous generations. Our study revealed that multigenerational exposure to cold stress resulted in the changes in the genome and epigenome (DNA methylation) across generations. Main changes in the progeny were due to the high frequency of genetic mutations rather than epigenetic changes; the difference was primarily in single nucleotide substitutions and deletions. The progeny of cold-stressed plants exhibited the higher rate of missense non-synonymous mutations as compared to the progeny of control plants. At the same time, epigenetic changes were more common in the CHG (C = cytosine, H = cytosine, adenine or thymine, G = guanine) and CHH contexts and favored hypomethylation. There was an increase in the frequency of C to T (thymine) transitions at the CHH positions in the progeny of cold stressed plants; because this type of mutations is often due to the deamination of the methylated cytosines, it can be hypothesized that environment-induced changes in methylation contribute to mutagenesis and may be to microevolution processes and that RNA-dependent DNA methylation plays a crucial role. Our work supports the existence of heritable stress response in plants and demonstrates that genetic changes prevail.
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    Non-coding RNAs match the deleted genomic regions in humans
    (Nature Research, 2016) Byeon, Boseon; Kovalchuk, Igor
    RNA is transcribed from DNA, and therefore, there should be no RNA transcript from the deleted DNA region. Our study attempted to analyse whether any RNA cache that maps the deleted regions is present in human cells. Using data from the 1000 genome project, we selected 41 CEPH (CEU) and 38 Yoruba (YRI) samples that included the data for the entire genome sequence and ncRNA and mRNA sequences. Aligning the ncRNA reads against the genomic DNA in individual samples has revealed that 229 out of 1114 homozygous deletions have ncRNA reads that map to them. Further analysis has revealed that ncRNA reads that map the deleted regions are enriched around the deletion ends and at genic regions of the genome. The read enrichment at deletion ends suggests that these ncRNAs are likely some form of double-strand break induced RNAs. Our analysis suggests that human cells may contain a residual ncRNA cache that is possibly propagated across generations.
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    Pattern recognition on read positioning in next generation sequencing
    (Public Library of Science, 2016) Byeon, Boseon; Kovalchuk, Igor
    The usefulness and the utility of the next generation sequencing (NGS) technology are based on the assumption that the DNA or cDNA cleavage required to generate short sequence reads is random. Several previous reports suggest the existence of sequencing bias of NGS reads. To address this question in greater detail, we analyze NGS data from four organisms with different GC content, Plasmodium falciparum (19.39%), Arabidopsis thaliana (36.03%), Homo sapiens (40.91%) and Streptomyces coelicolor (72.00%). Using machine learning techniques, we recognize the pattern that the NGS read start is positioned in the local region where the nucleotide distribution is dissimilar from the global nucleotide distribution. We also demonstrate that the mono-nucleotide distribution underestimates sequencing bias, and the recognized pattern is explained largely by the distribution of multinucleotides (di-, tri-, and tetra- nucleotides) rather than mono-nucleotides. This implies that the correction of sequencing bias needs to be performed on the basis of the multi-nucleotide distribution. Providing companion software to quantify the effect of the recognized pattern on read positioning, we exemplify that the bias correction based on the mono-nucleotide distribution may not be sufficient to clean sequencing bias.