The major histocompatibility complex (MHC) is one of the most variable regions in the vertebrate genome. Many genes within the MHC play important roles in the development of an immune response, including the response to pathogens, by presenting pathogen fragments to T cells. Pathogen-mediated balancing selection is thought to be important in maintaining the high levels of allelic variation at these loci, though the precise mechanism remains unclear. The number of studies of MHC diversity in non-model organisms has increased dramatically in recent years as genotype data have become cheaper and easier to generate; however, key limitations in many such studies remain a lack of high quality MHC genotypes and associated phenotype data. Many studies focus on a single MHC locus, assuming that one locus will represent the full range of variation within each MHC haplotype. Alternatively, the products of different loci may co-amplify, preventing locus-specific genotypes and hence heterozygosity being accurately determined. Non-model systems are also often limited by small sample sizes and limited recording of associated host and pathogen measures, which, combined with high levels of allelic variation at MHC loci, can limit statistical power. Finally, few MHC studies control for the general effect of relatedness in explaining host traits before testing for MHC effects. With so many methodological impediments, it is challenging to identify robust associations between MHC variation and host phenotypes, such as parasite burden or fitness, and to draw conclusions about the mechanisms underpinning the maintenance of diversity at MHC loci. In this thesis, I address these problems by developing a SNP-based haplotyping system for a population of unmanaged Soay sheep (Ovis aries) on Hirta, St. Kilda, for which data is available on pedigree, phenotypic traits and fitness and its components over a 30- year study period. The ovine MHC consists of four classes of loci, within which loci are tightly clustered and show reduced recombination rates compared to the genome average. Although the mammalian MHC is usually highly variable, one would expect that the number of haplotypes within an MHC class in an island population of sheep with no immigration to be limited. The class IIa region of the ovine MHC includes the classical class II loci which are typically thought to be involved in the presentation of peptides derived from extracellular pathogens, including gastrointestinal helminths, in sheep and other mammals. In chapters 2 to 4, I describe the characterisation of class IIa haplotypic diversity in the Soay sheep using direct Sanger sequencing of PCR amplified fragments, which, in combination with cloning, revealed eight distinct haplotypes. With this knowledge of haplotypic diversity, and genotypes for a sample of Soay sheep typed on the Ovine Infinium HD chip (approximately 600K SNPs), I developed a panel of 13 SNPs which could be used to impute the class IIa haplotypes. This panel was genotyped by KASP (Kompetitive Allele Specific PCR) in 6034 samples and used to impute the class IIa haplotypes. After quality control measures, class IIa haplotypes were successfully imputed for 5349 individuals. Evidence of balancing selection was identified using the Ewens-Watterson test at different life history stages and within the standing population each year between 1985 and 2012, showing that allele frequencies were more even than would be expected under neutrality. However, there was no evidence of deviation from Hardy-Weinberg equilibrium identified at different life stages or in the standing population in any year. In chapter 5, I investigate associations between the MHC class IIa haplotypes and individual-level data on host phenotypes - body weight, plasma immunoglobulin levels (measured as anti-Teladorsagia circumcincta third larval stage IgA, IgE and IgG) and strongyle faecal egg counts (FEC). Associations were tested within mixed effects models which were used to account for repeated measures and control for fixed effects known to affect the response variables, as well as within an animal model framework to account for relatedness between individuals. Haplotype heterozygosity was unrelated to any of the traits investigated, suggesting a general heterozygote advantage is unlikely to be operating within the Soay sheep. Six of the eight class IIa haplotypes were associated with multiple traits in different age-sex classes, although many of these associations were removed after inclusion within animal models. The evidence of balancing selection and associations between class IIa haplotypes and phenotypes related to health offers a promising glimpse into the evolutionary mechanisms which may be operating to maintain diversity within this region.

Submitted by Fabíola Silva (fabiola.silva@famerp.br) on 2017-09-29T18:21:41Z No. of bitstreams: 1 camilaravazzigauch_dissert.pdf: 1221932 bytes, checksum: 8184414238eac76d3bb5fced2b86cc83 (MD5) / Made available in DSpace on 2017-09-29T18:21:41Z (GMT). No. of bitstreams: 1 camilaravazzigauch_dissert.pdf: 1221932 bytes, checksum: 8184414238eac76d3bb5fced2b86cc83 (MD5) Previous issue date: 2015-12-03 / Introduction: The HLA (Human Leukocyte Antigen) molecules are proteins encoded by genes highly polymorphic and are involved in the immune response process. Polymorphisms of HLA genes differ between populations, both in frequency and in the presence or absence of specific alleles and haplotypes. Considering that the distribution of organs for transplant depends on HLA matching between donor and recipient, the knowledge and determination of the HLA polymorphism are of great importance in the process of allocation of organs for transplantation. Moreover, the knowledge of the HLA diversity is an important tool for studies of the origin of populations. Objectives: This study aimed to characterize the allele and haplotype frequencies of HLA-A, -B, and -DRB1 in a cohort of renal transplant candidates populations in the region of São José do Rio Preto (State of São Paulo), to compare the allele frequencies between Caucasian and Black in that region, as well as to compare these frequencies with different Brazilian populations reported. Materials and Methods: The HLA-A, -B, and -DRB1 allele and haplotypes frequencies were analyzed in a sample of 2.624 individuals and classified according to the ethnic group (2.347 Caucasians and 277 Blacks). The HLA class I (A, B) and class II (DRB1) specificities were determined by Complement-Dependent Microlymphocytotoxic (CDC) and Polymerase Chain Reaction/Sequence Specific Priming (PCR-SSP) methods, respectively. Results: All loci studied were in Hardy–Weinberg Equilibrium (p>0.05). Twenty-one HLA-A, 34 HLA-B and 13 HLA-DRB1 allelic groups were identified. The most frequent alleles for each locus were HLA-A*02, HLA-B*35, and HLA-DRB1*11. The most frequent haplotypes found were A*01 B*08 DRB1*03 among Caucasians and A*29 B*44 DRB1*07 among Blacks. Conclusions: The most common alleles for each locus among the renal transplant candidates were A*02, B*35 and DRB1*11. The most common haplotype was A*01 B*08 DRB1*03. The same haplotype was the most frequent in Caucasoid sample while the haplotype A*29 B*44 DRB1*07 was the most common in the Blacks sample. / Introdução: As moléculas HLA (Human Leucocyte Antigens) são proteínas codificadas por genes altamente polimórficos e estão envolvidas no processo de resposta imunológica. Os polimorfismos dos genes HLA diferem entre as populações, tanto na frequência como na presença ou ausência de alelos e haplotipos específicos, Considerando-se que a distribuição de órgãos para transplante depende da compatibilidade HLA entre doador e receptor, o conhecimento e determinação do polimorfismo HLA são de grande importância no processo de alocação de órgãos para transplantes, além de ser uma importante ferramenta em estudos populacionais. Objetivos: 1) Determinar as frequências alélicas para os locus HLA-A, -B e -DRB1 em uma amostra de candidatos a transplante renal no Brasil. 2)Determinar os haplótipos HLA mais freqüentes nessa amostra. 3) Comparar as diferenças de frequências alélicas e haplotípicas entre os grupos de caucasóides e negros da população analisada. Materiais e Métodos: As frequências alélicas e haplotípicas para os locus HLA-A, -B e -DRB1 foram analisadas em uma amostra de 2.624 candidatos a transplante renal e classificadas de acordo com o grupo étnico (2.347 Caucasóides e 277 Negros). As especificidades HLA de classe I (AB) e de classe II (DR) foram determinadas de acordo com a técnica Microlinfocitotóxica Dependente de Complemento (CDC) e Polymerase Chain Reaction - Sequence-specific Primers (PCR-SSP), respectivamente. Resultados: Considerando a amostra total, todos os loci estudados estavam em equilíbrio de Hardy-Weinberg (p>0,05). Foram identificados 21 grupos de alelos para o locus HLA-A, 34 para HLA-B e 13 para HLA-DRB1. Os alelos mais freqüentes para cada locus foram HLA-A*02, HLA-B*35 e HLA-DRB1*11. O haplótipo mais freqüente foi A*01 B*08 DRB1*03 entre a amostra de Caucasóides e A*29 B*44 DRB1*07 entre a amostra de Negros. Conclusões: Os alelos HLA mais freqüentes na população de candidatos a transplante renal foram HLA-A*02, HLA-B*35 e HLA-DRB*11. O haplótipo mais comum foi A*01 B*08 DRB1*03. Esse mesmo haplótipo foi o mais frequente na amostra de Caucasóide da população analisada enquanto que, A*29 B*44 DRB1*07 foi o mais comum na amostra de Negros.

Submitted by ALEJANDRA MARIA TORO OSPINA null (alejita-t_92@hotmail.com) on 2017-03-18T16:50:07Z No. of bitstreams: 1 dissertação_Alejandra_Toro.pdf: 1073618 bytes, checksum: 4de34349c23cb909c3128081fe41cc42 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2017-03-22T12:59:36Z (GMT) No. of bitstreams: 1 toroospina_am_me_jabo.pdf: 1073618 bytes, checksum: 4de34349c23cb909c3128081fe41cc42 (MD5) / Made available in DSpace on 2017-03-22T12:59:36Z (GMT). No. of bitstreams: 1 toroospina_am_me_jabo.pdf: 1073618 bytes, checksum: 4de34349c23cb909c3128081fe41cc42 (MD5) Previous issue date: 2017-02-24 / O objetivo deste estudo foi estimar o desequilíbrio de ligação (r2) nas distâncias de 25-50kb, 50-100kb, 100-500kb, 0,5-1Mb e o tamanho efetivo (Ne) nas gerações 0, 5, 10, 15, 20 em população da raça Gir selecionada para crescimento pós-desmama. Os animais utilizados no presente estudo foram provenientes do rebanho fechado do Instituto de Zootecnia, Sertãozinho, SP. Foram obtidos os genótipos de 155 animais com o painel BovineDL 33kb e 18 com painel HD imputado onde realizou-se controle de qualidade (CQ) para alelo de menor frequência (MAF) < 0,02 e call rate < 0,1. Depois do CQ permaneceram 27.236 SNPs e 155 animais do painel de 33 kb e 732.962 SNPs e 173 animais do painel HD Imputado. As análises de r2 foram realizadas pelo programa Plink e programa estatístico R Studio e o Ne por meio do DL. Os resultados das distâncias 25-50kb, 50-100kb, 100-500kb e 0,5-1Mb do r2 para o painel 33kb foram iguais a 0,29, 0,25, 0,16 e 0,032 respectivamente, e 0,35, 0,29, 0,18, 0,032 para o painel HD imputado demostrando que o DL permaneceu nas distâncias menores a 100kb, decaindo com o aumento das distâncias. Estes resultados foram maiores aos descritos na literatura para animais zebuínos, sugerindo como causa os segmentos longos de haplótipos que compartilham os animais aparentados. O Ne foi igual a 9, 17, 24, 30 e 30 animais nas gerações 0, 5, 10, 15, 20, observa-se que o Ne é maior na geração 20, com 30 animais, e decai drasticamente a partir da 5 geração com 17 animais, e sendo de 9 animais a última geração, um tamanho pequeno para uma população. Os valores encontrados neste estudo mostram alto DL e baixo Ne, provavelmente pelo sistema de seleção e a estrutura da população da raça Gir avaliada, que apresenta alto nível de endogamia, perda da variabilidade genética, uso intensivo de pequeno número de reprodutores, conduzindo a diminuição da deriva genética da população, ocasionando dificuldades na seleção dos animais. / The aim of this study was to estimate the linkage disequilibrium (r2) at distances of 25-50kb, 50-100kb, 100-500kb, 0,5-1Mb and the effective population size (Ne) in generations 0, 5, 10, 15, 20 in population of the selected Gir for yearling growth. The animals used in this study were from the closed herd Animal Science Institute, Sertãozinho, SP. the genotypes of 155 animals were obtained with BovineDL 33kb and 18 animals of panel HD, where quality control was held (QC) for minor allele frequency (MAF) <0.02 and call rate <0.1. After QC remained 27,236 SNPs and 155 animals to panel 33 kb, 732.962 SNPs and 173 the panel HD imputation. The r2 analyzes were performed by Plink program and R Studio statistical program and Ne through the DL. The results of r2 for distances 25-50kb, 50-100kb, 100-500kb and 0,5-1Mb were equal to 0.29, 0.25, 0.16 and 0.032, respectively, showing that the DL remained in smaller distances 100kb, decreasing with increasing distances. These results were higher than those reported in the literature for Zebu animals, suggesting a cause to long haplotype segments that share the related animals. Ne is equal to 9, 17, 24, 30 and 30 in the generations 0, 5, 10, 15, 20, it is observed that Ne is higher in generation 20 with 30 animals and decays sharply from 5 Generation 17 animals, and with 9 animals the latest generation, small size for a population. The values found in this study to DL and Ne, explain the selection system and the structure of the population of Gir evaluated, which has a high level of inbreeding, loss of genetic variability, intensive small number of players, leading to decreased drift population genetics, causing difficulties in the selection of the next generations.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Elevated total plasma homocysteine (tHcy) is a risk factor for cardiovascular disease and neurocognitive disease such as dementia. The B vitamins folate and B12 are the main de terminants of tHcy. tHcy concentration can also be affected by mutations in genes coding for receptors, enzymes and transporters important in the metabolism of Hcy. This thesis focuses on mutations in the genes for folate receptor-alpha and methylenetetrahydrofolate reductase (MTHFR) and the effect they have on tHcy concentrations. Six novel mutations in the gene for folate receptor-alpha were described in Paper I. Taken together they exist in a population with a prevalence of approximately 1% and thus are not unusual. There may be an association of –69dupA and –18C&gt;T to tHcy but for the 25-bp deletion, –856C&gt;T, –921T&gt;C and –1043G&gt;A there is probably no association to tHcy. Mutation screening was continued and four additional mutations, 1314G&gt;A, 1816delC, 1841G&gt;A and 1928C&gt;T, were described in Paper II. The prevalences for the heterozygotes were between 0.5% and 13% in an elderly population. There was no significant difference in prevalence between the elderly subjects and patients with dementia. The 1816(–)-allele and the 1841A-allele were in complete linkage and the haplotype 1816(–)-1841A may possibly have a tHcy raising effect. The 1314G&gt;A and 1928C&gt;T mutations had no association to tHcy. The genotype prevalences and haplotype frequencies of the MTHFR 677C&gt;T, 1298A&gt;C and 1793G&gt;A polymorphisms were determined in a population sample of Swedish children and adolescents (Paper III). The MTHFR 677T-allele was associated with increased tHcy concentrations in both children and adolescents. A small elevating effect of the 1298C-allele and a small lowering effect of the 1793A-allele could be shown. In an epidemiological sample of adults from the Canary Islands, Spain, data for serum folate and vitamin B12 were used for a broader study of the nutrigenetic impact on tHcy (Paper IV). The 677T-allele had a significant tHcy increasing effect in men but not in women. The 1298C-allele had a minor elevating effect on tHcy in men with the 677CT genotype. It was not possible to document any effect of the 1793A-allele on tHcy due to its low prevalence. A slightly superior explanatory power for the genetic impact was obtained using the MTHFR haplotypes in the analysis compared to the MTHFR 677C&gt;T genotype-based approach in both the Swedish children and adolescents and in the Spanish adults. Therefore MTHFR haplotypes should be considered when analysing the impact of the MTHFR 677C&gt;T, 1298A&gt;C and 1793G&gt;A polymorphisms on tHcy. Notwithstanding the large geographical distance between our study populations the haplotype composition is quite similar. The MTHFR 677T-allele is slightly more prevalent in Spain compared to Sweden but it has only an effect on tHcy in the Spanish men. Age, gender and factors linked to the ethnicity of the studied subjects, seem to be able to override the nutrigenetic impact of tHcy-raising genotypes or haplotypes in particular settings, such as in the Spanish women in our study. Gene-nutrient interactions on plasma tHcy levels thus may or may not exist in a certain population. The transferability of nutrigenetic findings may therefore be limited, and must be re-evaluated for each particular setting of age-gender-ethnicity.

Thesis (Ph.D. in Epidemiology) -- University of Colorado at Denver and Health Sciences Center, 2006. / Typescript. Includes bibliographical references (leaves 168-182). Free to UCDHSC affiliates. Online version available via ProQuest Digital Dissertations;

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 105-113).

Thesis (Ph.D.)--University of Alabama at Birmingham, 2008. / Title from first page of PDF file (viewed on June 23, 2009). Includes bibliographical references (p. 113-117).

Thesis (Ph. D.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Vita. Bibliography: 169-215.

Thesis (Ph. D.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Vita. Bibliography: 169-215.