Arctic charr is the most northerly distributed salmonid and the most abundant fish in high latitude postglacial lakes. Arctic charr lives in oligotrophic water bodies where it has been able to adapt and thrive due, in part, its noted outstanding phenotypic plasticity. Throughout its geographic range, the Arctic charr has had to specialize to get the most of each ecosystem, to the point that Arctic charr were originally described as 56 different species and only later considered as many phenotypic variations of the same group, called the Arctic charr complex. With the aim of using the resources available in areas with very low primary production, Arctic charr often specialize to become different morphotypes within the same water body. Each morphotype can follow different life histories that can be anadromous or non-migratory. In several lakes, the non-migratory stocks may also differentiate further, each form with its own trophic and/or reproductive behavior. Adult sympatric forms may differ in depth distribution, size-at-maturity, time and place of spawning, color and/or other meristic characters that include differential gill raker and vertebrae numbers. The two typical forms that are found in sympatry are a small, profoundal form often termed “dwarf” Arctic charr and a large, littoral or pelagic zone resident often termed “Normal” Arctic charr. The Arctic charr colonized most of its current habitat very recently, after the ice retreat in the late Pleistocene, 10000-15000 years ago. The reproductive isolation of stocks, if it has occurred at all, occurred so recently that the accumulated genetic drift often does not yield enough data to support the genetic separation of the stocks. Since the geographic borders of the stocks tend to be unclear and because the Arctic charr is a migratory species, the management of fisheries can be difficult in light of these issues, this thesis examines the potential for identifying Arctic charr populations using Major Histocompatibility (MH) genes as molecular markers. MH genes are useful because they are not neutral markers, but are subject to selection. MH receptors present peptides to T-lymphocytes and from that interaction the immune system defines what is self or non-self and thus whether or not immune reactions should be initiated. Due to the large variety of potential pathogenic peptides to be presented, the domain of the MH receptor that binds the peptide, the peptide binding region, is the most polymorphic coding region known. Each individual has a limited number of MH alleles. Given the high degree of polymorphism in populations it is virtually impossible that two individuals will share the same set, of MHC alleles with the exception of monozygotic twins. Since MH receptors present peptides derived from pathogens, they are related to disease resistance, and some MH alleles are more effective at presenting certain peptides than others. Therefore, populations settled in a specific niche will interact with a defined variety of pathogens that will select for certain patterns in the MH alleles of the population. The selection of these MH allelic patterns occurs rapidly, since they determine the survival of the individuals during disease outbreaks. Rapid selection means that MH allelic patterns they can be used to differentiate populations that have been separated for relatively short periods of time. The MH genes of Arctic charr had not been characterized before the publication of this thesis, so the first step was their isolation and characterization. We found the MH sequences obtained to have typical characteristics of classical MH receptors, sharing similarities with other salmonids and having most of their variation in the peptide binding region. We next characterized populations of Arctic charr selected from the global distribution using the three polymorphic MH receptors. For all of the receptor we found most of the polymorphisms distributed equally amongst the populations, but the interpopulation diversity was generally enough to differentiate at least some of the studied populations. For the MH Class I we studied three non classical (UCA, UGA, UEA) and one classical (UBA) gene. For UBA and UCA we found a large degree of polymorphism while UGA and UEA were not very polymorphic. Despite the fact that the UGA gene was also not polymorphic in studies of rainbow trout, we found the gene to be the best Class I population marker for Arctic charr because it had the highest relative rates of interpopulation diversity. Thus, UGA may be exhibiting some antigen presentation functions in Arctic charr. The population analysis using MH Class II α and Class II β genes were the most successful. Particularly in the case of Class II β, the analyses arose capable of differentiating all the populations chosen for this study. Both genes showed high levels of polymorphism and high rates of non-synonymous/synonymous substitution in the exon that encodes the peptide binding region. Lastly, we used MHC Class II α and Class II β to differentiate two separate sets of morphotypes living in sympatry in Lake Kiryalta in Russia and Gander Lake in Canada. The morphotypes in Gander Lake were successfully differentiated using both MH Class II α and β allele data, while the morphotypes in Lake Kiryalta were separated only with the MH Class II β allele data. Given that the use of one or more MH genes used allowed us to differentiate the populations studied, MH genes seem to be extremely useful as population markers for Arctic charr. Since MH genes not only characterize populations according to their phylogenetic relationships, but also according to their specific adaptation to inhabited niches, we concluded that all the Arctic charr populations studied are independent evolutionary significant units of the Arctic charr species. The conclusion implies that although different stocks might be living in sympatry, they should be considered as separate species for fishery and other management purposes, because their specific adaptations to the pathogens in their ecological niche might not allow them to cross-repopulate the other stock if it were removed by over-fishing or other anthropogenic stresses.

Arctic charr is the most northerly distributed salmonid and the most abundant fish in high latitude postglacial lakes. Arctic charr lives in oligotrophic water bodies where it has been able to adapt and thrive due, in part, its noted outstanding phenotypic plasticity. Throughout its geographic range, the Arctic charr has had to specialize to get the most of each ecosystem, to the point that Arctic charr were originally described as 56 different species and only later considered as many phenotypic variations of the same group, called the Arctic charr complex. With the aim of using the resources available in areas with very low primary production, Arctic charr often specialize to become different morphotypes within the same water body. Each morphotype can follow different life histories that can be anadromous or non-migratory. In several lakes, the non-migratory stocks may also differentiate further, each form with its own trophic and/or reproductive behavior. Adult sympatric forms may differ in depth distribution, size-at-maturity, time and place of spawning, color and/or other meristic characters that include differential gill raker and vertebrae numbers. The two typical forms that are found in sympatry are a small, profoundal form often termed “dwarf” Arctic charr and a large, littoral or pelagic zone resident often termed “Normal” Arctic charr. The Arctic charr colonized most of its current habitat very recently, after the ice retreat in the late Pleistocene, 10000-15000 years ago. The reproductive isolation of stocks, if it has occurred at all, occurred so recently that the accumulated genetic drift often does not yield enough data to support the genetic separation of the stocks. Since the geographic borders of the stocks tend to be unclear and because the Arctic charr is a migratory species, the management of fisheries can be difficult in light of these issues, this thesis examines the potential for identifying Arctic charr populations using Major Histocompatibility (MH) genes as molecular markers. MH genes are useful because they are not neutral markers, but are subject to selection. MH receptors present peptides to T-lymphocytes and from that interaction the immune system defines what is self or non-self and thus whether or not immune reactions should be initiated. Due to the large variety of potential pathogenic peptides to be presented, the domain of the MH receptor that binds the peptide, the peptide binding region, is the most polymorphic coding region known. Each individual has a limited number of MH alleles. Given the high degree of polymorphism in populations it is virtually impossible that two individuals will share the same set, of MHC alleles with the exception of monozygotic twins. Since MH receptors present peptides derived from pathogens, they are related to disease resistance, and some MH alleles are more effective at presenting certain peptides than others. Therefore, populations settled in a specific niche will interact with a defined variety of pathogens that will select for certain patterns in the MH alleles of the population. The selection of these MH allelic patterns occurs rapidly, since they determine the survival of the individuals during disease outbreaks. Rapid selection means that MH allelic patterns they can be used to differentiate populations that have been separated for relatively short periods of time. The MH genes of Arctic charr had not been characterized before the publication of this thesis, so the first step was their isolation and characterization. We found the MH sequences obtained to have typical characteristics of classical MH receptors, sharing similarities with other salmonids and having most of their variation in the peptide binding region. We next characterized populations of Arctic charr selected from the global distribution using the three polymorphic MH receptors. For all of the receptor we found most of the polymorphisms distributed equally amongst the populations, but the interpopulation diversity was generally enough to differentiate at least some of the studied populations. For the MH Class I we studied three non classical (UCA, UGA, UEA) and one classical (UBA) gene. For UBA and UCA we found a large degree of polymorphism while UGA and UEA were not very polymorphic. Despite the fact that the UGA gene was also not polymorphic in studies of rainbow trout, we found the gene to be the best Class I population marker for Arctic charr because it had the highest relative rates of interpopulation diversity. Thus, UGA may be exhibiting some antigen presentation functions in Arctic charr. The population analysis using MH Class II α and Class II β genes were the most successful. Particularly in the case of Class II β, the analyses arose capable of differentiating all the populations chosen for this study. Both genes showed high levels of polymorphism and high rates of non-synonymous/synonymous substitution in the exon that encodes the peptide binding region. Lastly, we used MHC Class II α and Class II β to differentiate two separate sets of morphotypes living in sympatry in Lake Kiryalta in Russia and Gander Lake in Canada. The morphotypes in Gander Lake were successfully differentiated using both MH Class II α and β allele data, while the morphotypes in Lake Kiryalta were separated only with the MH Class II β allele data. Given that the use of one or more MH genes used allowed us to differentiate the populations studied, MH genes seem to be extremely useful as population markers for Arctic charr. Since MH genes not only characterize populations according to their phylogenetic relationships, but also according to their specific adaptation to inhabited niches, we concluded that all the Arctic charr populations studied are independent evolutionary significant units of the Arctic charr species. The conclusion implies that although different stocks might be living in sympatry, they should be considered as separate species for fishery and other management purposes, because their specific adaptations to the pathogens in their ecological niche might not allow them to cross-repopulate the other stock if it were removed by over-fishing or other anthropogenic stresses.

Thesis (Ph. D.)--University of Chicago, Dept. of Biochemistry and Molecular Biology, 2002. / Includes bibliographical references. Also available on the Internet.

No description available.

Class I heavy chain (HC) must assemble with β-microglobulin (β2m) and acquire optimal peptide in order to be presented to cytotoxic T cells (CTLs). Calnexin is involved in the initial folding of class I HC and subsequent assembly with β2m. Incorporation of "empty" or suboptimally loaded class I molecules into the multimolecular loading complex is essential for them to acquire optimal peptides. The loading complex consists of several cofactors: TAP, tapasin, ERp57 and calreticulin. The precise role of calnexin and calreticulin in the regulated assembly and peptide loading and the significance of their physical interaction with other cofactors of the loading as well as preloading complex still remains unclear. Using mouse fibroblasts that lack calreticulin, I have studied the role of calreticulin in the assembly and loading of H2-K^b and H2-D^b expressed in these cells. MHC class I molecules in calreticulin-deficient cells are able to assemble with β2m normally, but their subsequent loading with optimal, stabilising peptides is defective despite their ability to interact with the TAP complex. The "empty" or suboptimally loaded class I molecules exit the ER rapidly. Reflecting the loading defect, presentation of endogenously processed antigens by class I molecules in calreticulin-deficient cells is impaired. I have used a human calnexin-deficient cell line CEM.NK^R to study assembly of class I in the absence of calnexin. The results demonstrate that contrary to current understanding, calnexin has an important role in class I HC assembly with 32- microglobulin. The role of heavy chain glycosylation in class I biogenesis is still controversial. My findings suggest asparagine (N)-linked glycosylation of human class I heavy chain at position 86 is optimal and any deviations from "normal" glycosylation results in poor loading with peptides and some defect in the assembly with β2m. Despite affecting the loading function, glycosylation did not have significant effect on presentation of a high affinity binding epitope to HLA-A*0201 specific CTLs. Finally, I show that co-operation from all domains of calreticulin is essential in order to generate a fully functional calreticulin. Interestingly, proline-rich (P) -domain of calreticulin downregulated expression of a number of cellular proteins including MHC class I HC, despite restoring the cytosolic calcium levels in calreticulindeficient cells. The effect of P-domain on class I expression was at the level of transcription.

No description available.

This work examines the ecological, social and genetic factors that predispose amphibians to infection. In the last 30 years many amphibian populations have declined due to infectious disease, although few researchers have studied the factors involved in mediating amphibian infection. My research is designed to explore some of these factors. I first examined the effects of crowding, kin composition (the relatedness of individuals in a group), and habitat complexity on the growth and survival of Xenopus laevis tadpoles exposed to the bacterial pathogen Aeromonas hydrophila. In tadpoles, stress, and in particular corticosterone, a hormone associated with stress, is known to inhibit growth. Crowding, kin composition, and habitat complexity have all been linked to tadpole growth. As corticosterone exposure is also linked to reduced immune function, I examined how these ecological factors influence tadpoles' disease resistance. Tadpoles exposed to the bacterium were significantly smaller and more likely to die than control tadpoles. Tadpoles reared only with siblings (pure sibship groups) were larger, less variable in size, and had lower mortality rates than tadpoles reared in mixed sibship groups. The size difference between pure and mixed sibship groups was greatest when they were exposed to the pathogen. Habitat complexity reduced size variation within tanks but did not affect mean tadpole size. Mixed kinship composition and high tadpole density can increase competition, reduce growth, and increase disease susceptibility. These results indicate that growth was inhibited by pathogen exposure but kin association may ameliorate this effect. The Major Histocompatibility Complex (MHC) is an integral part of the vertebrate adaptive immune system. To determine the importance of the MHC in conferring disease resistance in amphibians, I challenged X. laevis tadpoles, bearing different combinations of four MHC haplotypes (f, g, j, and r), with A. hydrophila in two experiments. Exposure to A. hydrophila affected the growth and survival of these tadpoles and that the MHC moderated these effects. Tadpoles with two MHC haplotypes (r and g) were susceptible to this pathogen and tadpoles with the other two haplotypes (f and j) were resistant. Heterozygous tadpoles with both susceptible and resistant haplotypes were always intermediate to either homozygotes in size and survival. These results demonstrate that MHC genotype plays a major role in determining the impact of bacterial pathogens on the growth and survival of X. laevis tadpoles. To test whether the effect of exposure to pathogens differs according to the similarity of the hosts I challenged tadpoles with natural levels of the microorganisms associated with different MHC genotypes by exposing the tadpoles to water preconditioned by adults of different MHC genotypes. If the pathogens are adapted to the MHC genotype of their hosts, tadpoles exposed to water from adults with which they shared MHC haplotypes would be more susceptible than those exposed to water from MHC-dissimilar adults. Alternatively, if the hosts are adapted to their pathogens tadpoles may be more resistant to pathogens from MHC-similar frogs than those from MHC-dissimilar frogs. I found that tadpoles exposed to water from MHC-dissimilar animals developed faster, but without increased growth, and were more likely to die than those exposed to water from MHC-similar animals. Furthermore, there was an optimal difference between the tadpoles’ and the donors’ MHC where tadpoles were sufficiently different to the donor to defend against its locally adapted pathogens, and sufficiently similar to not be exposed to especially virulent foreign pathogens. Finally, I present an inventory of bacteria found in the gut and skin (nonsystemic sites) and heart, muscle, and abdominal cavity (systemic sites) of captive frogs. I found several species of bacteria previously identified as amphibian pathogens and many bacteria in systemic sites that have not been considered pathogenic to amphibians. None of the frogs tested positive for the amphibian chytrid fungus, Batrachochytrium dendrobatidis. I discuss the potential importance of these species of bacteria as amphibian pathogens and as protective probiotics, using New Zealand frogs as a case study. In its sum, this work describes some of the factors that can affect amphibians’ ability to resist disease. I show that the genetic constitution of an individual, specifically in terms of the MHC, affects the impact of a disease, and so too does its social and ecological conditions, including the level of crowding, the kinship of its groupmates and the specific microbial challenges of its immediate environment. I also show that many of the factors linked to tadpole growth and development that are well described in other amphibians also affect Xenopus tadpoles.

Dissertation (Ph.D.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 54-58). Also available via the Internet.

Thesis (M.S.)--Georgia State University, 2006. / Title from title screen. Susanna Greer, committee chair; Delon Barfus,Yuan Liu, committee members. Electronic text (72 p. : ill.) : digital, PDF file. Description based on contents viewed Aug. 20, 2007. Includes bibliographical references (p. 69-72).