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Molecular evolutionary studies on major histocompatibility complex and amylase genes in Eurasian badgers, genus Meles (Mammalia, Carnivora, Mustelidae)

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Title: Molecular evolutionary studies on major histocompatibility complex and amylase genes in Eurasian badgers, genus Meles (Mammalia, Carnivora, Mustelidae)
Other Titles: ユーラシアアナグマMeles属における主要組織適合遺伝子複合体とアミラーゼ遺伝子に関する分子進化学的研究
Authors: 阿不都热依木, 夏米西丁 Browse this author
Issue Date: 25-Sep-2018
Abstract: Duplicated genes in the genome play important roles in biological activities in organisms. In the present study, major histocompatibility complex (MHC) genes and amylase genes known as the dupl icated genes were investigated in four related species of Eurasian badgers, genus Meles . Through the investigation, interesting characteristics on the genes were newly found as follows. The MHC genes encode proteins that play an indispensable role in the a daptive immune system and autoimmunity of vertebrates, to defense against diverse spectrum of pathogens. To further understand the variation and evolution of MHC genes, including both class I (MHCI) and class II gene in the four Eurasian badger species (Eu ropean badger Meles meles , Southwest Asian badger M. canescenes , Asian badger M. leucurus and Japanese badger M. anakuma ), genus Meles , the most polymorphic region exon 2 of MHC class II DRB gene, exons 2 and 3 and intervening intron 2 of MHC class I gene were concentratively targeted to analyse. According to the results obtained, it was found that altogether 60 MHC DRB and 64 MHCI alleles were isolated from 28 and 25 badger individuals, respectively. Among which 4 of MHC DRB and 9 of MHCI were putative pse udogenes with indels or stop codons. Both exons 2 of MHC DRB and MHCI, but not exon 3 of MHCI, accumulated extensive nonsynonymous than synonymous substitutions at the antigen binding sites (ABSs), indicating historical positive selection. Both recombinati on and codon based positive selection analyses exhibited signatures of recombination and positive selection in both MHC DRB and MHCI genes in these Eurasian badgers, implying that both recombination and selection more likely act on the driving and maintain ing of polymorphism in MHC gene in the genus Meles . Separate phylogenetic analyses for exons 2 of MHC DRB and exons 2 and 3 and intron 2 of MHCI showed trans - species polymorphisms at different taxonomic scales, transgressing family - , genus - and species - lev el splits, which are indirect evidence of long term balancing selection. A s maller number of shared alleles and higher number of pseudogenes were observed in MHCI genes compared to MHC DRB gene . This is consistent with the faster turnover rate of typical M HC class I loci r elative to that of MHC class II. Owing to various degrees of MHCI divergence, a number of nonclassical genes and pseudogenes are generated from their counterparts — classical genes . A mylase genes code for digestive enzyme amylases, whic h are important in catalysis of starch into maltose in the oral, stomach, and intestine of mammals. To get insight into the copy number variation (CNV) of amylase genes and its relationship to diet, the partial exon 4 of amylase gene was amplified in the r eal time quantitative PCR system. The results showed that only Asian badger among the four Eurasian badgers studied was found to be with varied amylase copy numbers between one and four. Within Asian badger, populations also presented significantly differe ntiated CNVs one another, This suggests that Asian badger is better adapted to a diet rich in starch and/or glycogen than its congeners. As Eurasian badgers are basically omnivorous but favour a animal diet, it is speculated that the CNV is related to the seasonal dearth of animal food in the range of Asian badger, which enforces a more vegetal diet. This in turn would favour more efficient digestion of dietary starch, which could be achieved by increasing the copy number of the pancreatic amylase gene. The above achievements were presented in three different Chapters I, II, and III. Chapter I mainly included the results and interpretations of the MHC class II genes in the four Eurasian badgers, which published in Biological Journal of The Linnean Society in October, 2017 ( ) . While Chapter II comprised of the results and interpretations of the MHC class I genes in the four Eurasian badgers, of which the data are online published in Heredity in June, 2018 ( - 018 - 0100 - 3 or full - text view - only at ) . Lastly, Chapter III prese nted the results and interpretations of the amylase gene copy number variation in the four Eurasian badger s and related taxa in Mustelid , which have been under review in an international journal , too.
Conffering University: 北海道大学
Degree Report Number: 甲第13315号
Degree Level: 博士
Degree Discipline: 理学
Examination Committee Members: (主査) 教授 増田 隆一, 教授 堀口 健雄, 教授 高木 昌興, 准教授 加藤 徹
Degree Affiliation: 理学院(自然史科学専攻)
Type: theses (doctoral)
Appears in Collections:課程博士 (Doctorate by way of Advanced Course) > 理学院(Graduate School of Science)
学位論文 (Theses) > 博士 (理学)

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