| Summary: | 碩士 === 中山醫學大學 === 生物醫學科學學系碩士班 === 104 === Protein arginine methyltransferases (PRMTs) preform posttranslational modification involved in transcriptional regulation, RNA processing and many different cellular processes. Nine prmt genes are conserved in vertebrates, while prmt1, 2, 4 and 6 are not present in avian. Among these prmt1 is the most conserved and widely distributed prmt gene in eukaryotes, and its deletion is embryonic lethal in mouse. No prmt1 but only its vertebrate paralogue prmt8 could be identified in birds. As avian underwent large segmental chromosomal deletions and gene loss during their evolution, we first determined whether in birds the prmt1 gene was specifically eliminated alone or with neighboring chromosomal segments. We obtained 11 downstream and upstream genes of prmt1 and prmt8 in typical vertebrate species as shown in the UCSC genome browser, collected their homologous genes in other species by BLAST, and then recorded and compared their chromosome localizations. In pair-wise species comparison, orthologous genes near prmt8 have higher conserved level and more gene clusters than prmt1. As most vertebrate type I PRMTs (PRMT1, 2, 3, 4, 6, and 8) that catalyze the formation of asymmetric dimethylarginine (ADMA) are missing in avian, we are interested in whether the ADMA level in birds may be lower than that in other vertebrates. We prepared brain, liver and muscle extracts from chicken and mouse. The ADMA levels were not reduced in different chicken tissues as shown by western blot analyses with an ADMA-specific antibody. We then suspected that loss of prmt1 may be compensated by its paralogue prmt8. However, as shown by RT-PCR analyses, prmt8 mRNA expression was still brain-specific in chicken. It is thus unlikely that prmt8 can complement the loss other type I PRMTs. We also fractionated mouse and chicken brain tissue to examine the PRMT distribution pattern. The result reveals subcellular distribution of type I PRMTs in chicken and mouse have high similarity. Furthermore, in vitro methylation revealed that chicken brain still has similar capability to catalyze arginine methylation as mouse brain extract. Our study provides information about chromosome rearrangement and syntenic blocks deletion near prmt1 in avian evolution. Chicken can be considered as a natural multiple prmt-deleted biological system to further elucidate the critical function of protein arginine methylation conserved and not conserved in vertebrates.
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