Faculty Bibliography

As an anti-inflammatory mediator IL10 is beneficial in certain contexts and deleterious in others. As increased production of IL10 favours protection against inflammatory disease, whereas low production promotes elimination of foreign pathogens by the host, we investigated the possible influence of balancing selection at this locus. We began by resequencing 48 European and 48 African chromosomes across 2.2 kb of the IL10 promoter region, and compared this with four neighbouring gene regions: MK2, IL19, IL20 and IL24. Analysis of nucleotide diversity showed a positive Tajima's D-test for IL10 in Europeans, of borderline statistical significance (1.89, P=0.05). Analysis of F(st) values showed significant population divergence at MK2, IL19, IL20 and IL24 (P<0.01) but not at IL10. Taken together, these findings are consistent with the hypothesis that balancing selection has played a role in the evolution of polymorphisms in the IL10 promoter region.

There is presently much interest in utilizing patterns of linkage disequilibrium (LD) to further genetic association studies. This is particularly pertinent in the class III region of the human major histocompatibility complex (MHC), which has been extensively studied as a disease susceptibility locus in a number of ethnic groups. To date, however, few studies of LD in the MHC have considered non-Caucasian populations. With the advent of large-scale haplotyping of the human genome, the question of utilizing LD patterns across populations has come to the fore. We have previously used LD mapping to direct an MHC class III association study in a UK Caucasian population. As an extension of this, we sought to determine to what extent the pattern of LD observed in that study could be used to conduct a similar study in a West African Gambian population. We found that broad patterns of LD were similar in the two populations, resulting in similar candidate region delineations, but at a higher resolution, marker-specific patterns of LD and population-dependent allele frequencies confounded the choice of regional tagging SNPs. Our results have implications for the applicability of large-scale haplotype maps such as the HapMap to complex regions like the MHC.

Dyslexia is one of the most prevalent childhood cognitive disorders, affecting approximately 5% of school-age children. We have recently identified a risk haplotype associated with dyslexia on chromosome 6p22.2 which spans the TTRAP gene and portions of THEM2 and KIAA0319. Here we show that in the presence of the risk haplotype, the expression of the KIAA0319 gene is reduced but the expression of the other two genes remains unaffected. Using in situ hybridization, we detect a very distinct expression pattern of the KIAA0319 gene in the developing cerebral neocortex of mouse and human fetuses. Moreover, interference with rat Kiaa0319 expression in utero leads to impaired neuronal migration in the developing cerebral neocortex. These data suggest a direct link between a specific genetic background and a biological mechanism leading to the development of dyslexia: the risk haplotype on chromosome 6p22.2 down-regulates the KIAA0319 gene which is required for neuronal migration during the formation of the cerebral neocortex.

Genetic variation at the human LTA locus, encoding lymphotoxin-alpha, is associated with susceptibility to myocardial infarction, asthma and other diseases. By detailed haplotypic analysis of the locus, we identified a single-nucleotide polymorphism (SNP) at LTA+80 as a main predictor of LTA protein production by human B cells. We found that activated B-cell factor-1 (ABF-1) binds to this site in vitro and suppresses reporter gene expression, but only in the presence of the LTA+80A allele. Using haplotype-specific chromatin immunoprecipitation, we confirmed that ABF-1 is preferentially recruited to the low-producer allele in vivo. These findings provide a molecular model of how LTA expression may be genetically regulated by allele-specific recruitment of the transcriptional repressor ABF-1.

In vivo characterization of regulatory polymorphisms is a key requirement for next-generation human genetic analysis. Here we describe haploChIP, a method that uses chromatin immunoprecipitation (ChIP) and mass spectrometry to identify differential protein-DNA binding in vivo associated with allelic variants of a gene. We demonstrate this approach with the imprinted gene SNRPN. HaploChIP showed close correlation between the level of bound phosphorylated RNA polymerase II at the SNRPN locus and allele-specific expression. Application of the approach to the TNF/LTA locus identified functionally important haplotypes that correlate with allele-specific transcription of LTA. The haploChIP method may be useful in high-throughput screening for common DNA polymorphisms that affect gene regulation in vivo.