Meeting Abstract
Regulation of the innate immune system (e.g. inflammation) has been implicated as mediator of vertebrate range expansions. Previous research from our lab has shown that leukocyte expression of Toll-like receptor 4 (TLR-4), the major surveillance molecule for Gram-negative bacteria, varied among Kenyan house sparrow (Passer domesticus ) populations of different ages: individuals at the range-edge expressed more TLR-4 than individuals at the site of introduction. Given that genetic diversity is relatively low in this introduced range, epigenetic variation, namely DNA methylation, may unmask phenotypic variation in response to novel environments. Further, we know that at the population-level, neutral genetic variation is inversely correlated to genome-wide DNA methylation. Here, we investigated DNA methylation within the TLR-4 promoter in the liver—an immunologically important tissue—asking whether i) methylation was correlated to hepatic TLR-4 expression within individuals and ii) whether the extent of methylation and/or its effects on expression differed among populations of different age. We predicted the least DNA methylation (and the most hepatic TLR-4 expression) in range edge birds, while we expected similar relationships between expression and methylation among populations. Our initial findings provide evidence of high CpG diversity (i.e. CpG-SNPS) within the avian TLR-4 promoter, in just a few individuals sampled so far. Further analysis will indicate whether diversity at the population-level influences the potential for epigenetic regulation of TLR-4 in invasive Kenyan sparrows. Such studies will provide insight into the importance of molecular-level mechanisms for influencing physiological and/or organismal-level responses to rapid environmental change.
