Biology subjects

Hollox, E.

Publications and source records attributed to Hollox, E..

4 recordsLinked to original sources

bioRxiv2021

Maintenance of copy number variation at the human salivary agglutinin gene (DMBT1) by balancing selection driven by host-microbe interactions

Most genetic variation in humans occurs in a pattern consistent with neutral evolution, but a small subset is maintained by balancing selection. Identifying loci under balancing selection is important not only for understanding the processes explaining variation in the genome, but also to identify loci with alleles that affect response to the environment and disease. Several genome scans using genetic variation data have identified the 5 end of the DMBT1 gene as a region undergoing balancing selection. DMBT1 encodes the pattern-recognition glycoprotein DMBT1, also known as SALSA, gp340 or salivary agglutinin. It binds to a wide variety of pathogens through a tandemly-arranged scavenger receptor cysteine-rich (SRCR) domain, with the number of SRCR domains varying in humans. Here we use expression analysis, linkage in pedigrees, and long range single transcript sequencing, to show that the signal of balancing selection is driven by one haplotype usually carrying shorter SRCR repeats, and another usually carrying a longer SRCR repeat, within the coding region of DMBT1. The DMBT1 protein size isoform encoded by a shorter SRCR domain repeat allele showed complete loss of binding of a cariogenic and invasive Streptococcus mutans strain in contrast to the long SRCR allele. Taken together, our results suggest that balancing selection at DMBT1 is due to host-microbe interactions of encoded SRCR tandem repeat alleles.

genetics↗

bioRxiv2019

Genotyping complex structural variation at the malaria-associated human glycophorin locus using a PCR-based strategy

Structural variation in the human genome can affect risk of disease. An example is a complex structural variant of the human glycophorin gene cluster, called DUP4, which is associated with a clinically-significant level of protection against severe malaria. The human glycophorin gene cluster harbours at least 23 distinct structural variants and accurate genotyping of this complex structural variation remains a challenge. Here, we use a PCR-based strategy to genotype structural variation at the human glycophorin gene cluster. We validate our approach, based on a triplex paralogue ratio test (PRT) combined with junction-fragment specific PCR, on publically-available samples from the 1000 Genomes project. We then genotype a longitudinal birth cohort using small amounts of DNA at low cost. Our approach readily identifies known deletions and duplications, and can potentially identify novel variants for further analysis. It will allow exploration of genetic variation at the glycophorin locus, and investigation of its relationship with malaria, in large sample sets at minimal cost, using standard molecular biology equipment.

genetics↗

bioRxiv2018

The malaria-protective human glycophorin structural variant DUP4 shows somatic mosaicism and association with hemoglobin levels

Glycophorin A and glycophorin B are red blood cell surface proteins that are both receptors for the parasite Plasmodium falciparum, which is the principal cause of malaria in sub-Saharan Africa. DUP4 is a complex structural genomic variant that carries extra copies of a glycophorin A - glycophorin B fusion gene, and has a dramatic effect on malaria risk by reducing the risk of severe malaria by up to 40%. Using fiber-FISH and Illumina sequencing, we validate the structural arrangement of the glycophorin locus in the DUP4 variant, and reveal somatic variation in copy number of the glycophorin A-glycophorin B fusion gene. By developing a simple, specific, PCR-based assay for DUP4 we show the DUP4 variant reaches a frequency of 13% in a village in south-eastern Tanzania. We genotype a substantial proportion of that village and demonstrate an association of DUP4 genotype with hemoglobin levels, a phenotype related to malaria, using a family-based association test. Taken together, we show that DUP4 is a complex structural variant that may be susceptible to somatic variation, and show that it is associated with a malarial-related phenotype in a non-hospitalized population.\n\nSignificance statementPrevious work has identified a human complex genomic structural variant called DUP4, which includes two novel glycophorin A-glycophorin B fusion genes, is associated with a profound protection against severe malaria. In this study, we present data showing the molecular basis of this complex variant. We also show evidence of somatic variation in the copy number of the fusion genes. We develop a simple robust assay for this variant and demonstrate that DUP4 is at an appreciable population frequency in Tanzania and that it is associated with higher hemoglobin levels in a malaria-endemic village. We suggest that DUP4 is therefore protective against malarial anemia.

genetics↗

bioRxiv2018

Complement receptor 1 gene (CR1) intragenic duplication and risk of Alzheimer’s disease

Single nucleotide variants (SNVs) within and surrounding the complement receptor 1 (CR1) gene show some of the strongest genome-wide association signals with late-onset Alzheimers disease. Some studies have suggested that this association signal is due to a duplication allele (CR1-B) of a low copy repeat (LCR) within the CR1 gene, which increases the number of complement C3b/C4b-binding sites in the mature receptor. In this study, we develop a triplex paralogue ratio test (PRT) assay for CR1 LCR copy number allowing large numbers of samples to be typed with a limited amount of DNA. We also develop a CR1-B allele-specific PCR based on the junction generated by an historical non-allelic homologous recombination event between CR1 LCRs. We use these methods to genotype CR1 and measure CR1-B allele frequency in both late-onset and early-onset cases and unaffected controls from the United Kingdom. Our data support an association of late-onset Alzheimers disease with the CR1-B allele, and confirm that this allele occurs most frequently on the risk haplotype defined by SNV alleles. Furthermore, regression models incorporating CR1-B genotype provide a bitter fit to our data compared to incorporating the SNP-defined risk haplotype, supporting the CR1-B allele as the variant underlying the increased risk of late-onset Alzheimers disease.

genetics↗