Gene Expression Contributes to the Recent Evolution of Host Resistance in a Model Host Parasite System

Heritable population differences in immune gene expression following infection can reveal mechanisms of host immune evolution. We compared gene expression in infected and uninfected threespine stickleback (Gasterosteus aculeatus) from two natural populations that differ in resistance to a native cestode parasite, Schistocephalus solidus. Genes in both the innate and adaptive immune system were differentially expressed as a function of host population, infection status, and their interaction. These genes were enriched for loci controlling immune functions known to differ between host populations or in response to infection. Coexpression network analysis identified two distinct processes contributing to resistance: parasite survival and suppression of growth. Comparing networks between populations showed resistant fish have a dynamic expression profile while susceptible fish are static. In summary, recent evolutionary divergence between two vertebrate populations has generated population-specific gene expression responses to parasite infection, affecting parasite establishment and growth

Designing eco-evolutionary experiments for restoration projects: Opportunities and constraints revealed during stickleback introductions.

Eco-evolutionary experiments are typically conducted in semi-unnatural controlled settings, such as mesocosms; yet inferences about how evolution and ecology interact in the real world would surely benefit from experiments in natural uncontrolled settings. Opportunities for such experiments are rare but do arise in the context of restoration ecology-where different "types" of a given species can be introduced into different "replicate" locations. Designing such experiments requires wrestling with consequential questions. (Q1) Which specific "types" of a focal species should be introduced to the restoration location? (Q2) How many sources of each type should be used-and should they be mixed together? (Q3) Which specific source populations should be used? (Q4) Which type(s) or population(s) should be introduced into which restoration sites? We recently grappled with these questions when designing an eco-evolutionary experiment with threespine stickleback (Gasterosteus aculeatus) introduced into nine small lakes and ponds on the Kenai Peninsula in Alaska that required restoration. After considering the options at length, we decided to use benthic versus limnetic ecotypes (Q1) to create a mixed group of colonists from four source populations of each ecotype (Q2), where ecotypes were identified based on trophic morphology (Q3), and were then introduced into nine restoration lakes scaled by lake size (Q4). We hope that outlining the alternatives and resulting choices will make the rationales clear for future studies leveraging our experiment, while also proving useful for investigators considering similar experiments in the future

Multiple mechanisms cooperate to enforce antigen receptor allelic exclusion

The adaptive immune system requires a diverse repertoire of antigen receptors to effectively respond to pathogens. Antigen receptor diversity is generated through the recombination of variable (V), diversity (D), and joining (J) gene segments in developing B and T lymphocytes. Though all lymphocytes contain two allelic copies of antigen receptor loci most recombine and express receptor chains from a single allele, a phenomenon known as allelic exclusion . Early experiments in the 1980s identified that an antigen receptor chain expressed from one allele signaled feedback inhibition of V-to-(D)J recombination on the other allele. However, more recent findings suggest that additional mechanisms contribute to the mono-allelic expression of antigen receptor chains. The data presented in this thesis uses various mouse models to discover and investigate three mechanisms that regulate antigen receptor allelic exclusion. First, posttranscriptional silencing of functional VβDJβ rearrangements ensures the mono-allelic expression of TCRβ genes. Second, the DNA damage response protein, ATM, enforces Igκ, IgH, and TCRβ allelic exclusion, suppresses bi-allelic rearrangements at these loci, and inhibits RAG expression. Lastly, the cell cycle protein, cyclin D3 functions alone and in cooperation with ATM to enforce IgH and TCRβ allelic exclusion. Together, these data demonstrate that multiple, successive mechanism have evolved to prevent the bi-allelic rearrangement and expression of antigen receptor genes

Multiple mechanisms cooperate to enforce antigen receptor allelic exclusion

The adaptive immune system requires a diverse repertoire of antigen receptors to effectively respond to pathogens. Antigen receptor diversity is generated through the recombination of variable (V), diversity (D), and joining (J) gene segments in developing B and T lymphocytes. Though all lymphocytes contain two allelic copies of antigen receptor loci most recombine and express receptor chains from a single allele, a phenomenon known as allelic exclusion . Early experiments in the 1980s identified that an antigen receptor chain expressed from one allele signaled feedback inhibition of V-to-(D)J recombination on the other allele. However, more recent findings suggest that additional mechanisms contribute to the mono-allelic expression of antigen receptor chains. The data presented in this thesis uses various mouse models to discover and investigate three mechanisms that regulate antigen receptor allelic exclusion. First, posttranscriptional silencing of functional VβDJβ rearrangements ensures the mono-allelic expression of TCRβ genes. Second, the DNA damage response protein, ATM, enforces Igκ, IgH, and TCRβ allelic exclusion, suppresses bi-allelic rearrangements at these loci, and inhibits RAG expression. Lastly, the cell cycle protein, cyclin D3 functions alone and in cooperation with ATM to enforce IgH and TCRβ allelic exclusion. Together, these data demonstrate that multiple, successive mechanism have evolved to prevent the bi-allelic rearrangement and expression of antigen receptor genes

TCRβ Feedback Signals Inhibit the Coupling of Recombinationally Accessible Vβ14 Segments with DJβ Complexes

Ag receptor allelic exclusion is thought to occur through monoallelic initiation and subsequent feedback inhibition of recombinational accessibility. However, our previous analysis of mice containing a V(D)J recombination reporter inserted into Vβ14 (Vβ14[superscript Rep]) indicated that Vβ14 chromatin accessibility is biallelic. To determine whether Vβ14 recombinational accessibility is subject to feedback inhibition, we analyzed TCRβ rearrangements in Vβ14[superscript Rep] mice containing a preassembled in-frame transgenic Vβ8.2Dβ1Jβ1.1 or an endogenous Vβ14Dβ1Jβ1.4 rearrangement on the homologous chromosome. Expression of either preassembled VβDJβC β-chain accelerated thymocyte development because of enhanced cellular selection, demonstrating that the rate-limiting step in early αβ T cell development is the assembly of an in-frame VβDJβ rearrangement. Expression of these preassembled VβDJβ rearrangements inhibited endogenous Vβ14-to-DJβ rearrangements as expected. However, in contrast to results predicted by the accepted model of TCRβ feedback inhibition, we found that expression of these preassembled TCR β-chains did not downregulate recombinational accessibility of Vβ14 chromatin. Our findings suggest that TCRβ-mediated feedback inhibition of Vβ14 rearrangements depends on inherent properties of Vβ14, Dβ, and Jβ recombination signal sequences