| Aging is becoming one of the important processes concerned by more and more people, as a result of joint action of external environmental and inherent genetic factors. The inherent genetic mechanism is mainly influenced by forming DNA and RNA monomers and the chemical structures of coding genetic information. In addition to A, T, G, and C, the5mC (5-methylcytosine), as the fifth base, is becoming a critical epigenetic marker widely concerned by biologists today. The5mC located in DNA may alter the chromatin structure in corresponding genomic region, enhance the spiralization and bunching of the chromatin, thus suppress the transcriptional activity of DNA. Meanwhile, the functions of RNA (especially mRNA) methylation at the5position of cytocine, such as its influence on aging, is still unclear and need to be investigated. The Chinese rhesus macaque (Macaca mulatto) is one of non-human primates with similar biological attributes and genetic background to human beings. It has an advantage over rodent models in aging-related studies, and was regarded as ideal models for inverstigation of human immunodeficiency. In the present study, the distribution of5mC in the transcriptome of rhesus macaques is investigated to examine possible association between5mC and aging, using the methods of mRNA Sodium bisulfite treatment and second-generation sequencing. The major conclusions are as follows:(1)5mC was unevenly distributed across different gene regions:introns (3500) account for44.2%of the total5mC sites, while exons (2346) account for29.7%5mC sites; in exons, nearly95percent of5mC methylation occurred at synonymous sites; rather fewer5mC methylation was observed at alternative splicing sites, indicating that5mC may affect splicing, and changes at alternative splicing sites are suppressed in mRNA.(2) Comparisons of numbers of the reads and coverages indicated that, the more the coverage, the greater the number of sites, especially in introns.(3) Analysis of5mC in the spleen tissue revealed that aged macaque has about half of the5mC methylation as in younger macaque, indicating that the aged individual may had experienced severer degeneration of their immune system. This implies that5mC in mRNA has definite links to aging.(4) As revealed by the GO annotation analyses, genes containing5mC which been mapped in the spleen tissue of both the young and aged macaques are mostly of functions of cell apoptosis, implying that5mC plays some important roles in programmed cell death, thus was linked to aging.(5) In the six sorts of tissues of both the young and aged macaques, most of the5mC-mapped genes cluster to the functions of apoptosis, macromolecules hydrolyzation, protein transportion, signal transduction, phosphoric acid metabolic process, redox process, and other functions, suggesting that5mC are widely distributed, being located in genes of varied important functions in organisms.In lung and liver tissues of aged macaque,5mC-methylated genes clustered to apoptosis functions, further indicating that5mC is associated with aging.(6) Both the NSUN2(NOP2/Sun RNA methyltransferase family, member2) and TRDMT1(tRNA aspartic acid methyltransferase1) genes are expressed in macaque, while the former one has relatively lower expression, probably due to different in vivo functional universality between the two genes.In summary, our study clearly suggest that,5mC methylation is associated with aging by affecting varied functions in different type of tissues, for example, RNA splicing, immune system degradation, apoptosis, and so on. |
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