Pepperell, C. | bioRxiv Science

bioRxiv2021

Transcriptional and translational responsiveness of the Neisseria gonorrhoeae type IV secretion system to conditions of host infections

The type IV secretion system of Neisseria gonorrhoeae translocates single-stranded DNA into the extracellular space, facilitating horizontal gene transfer and initiating biofilm formation. Expression of this system has been observed to be low under laboratory conditions, and multiple levels of regulation have been identified. We used a translational fusion of lacZ to traD, the gene for the type IV secretion system coupling protein, to screen for increased type IV secretion system expression. We identified several physiologically relevant conditions, including surface adherence, decreased manganese or iron, and increased zinc or copper, which increase gonococcal type IV secretion system protein levels through transcriptional and/or translational mechanisms. These metal treatments are reminiscent of the conditions in the macrophage phagosome. The ferric uptake regulator, Fur, was found to repress traD transcript levels, but to also have a second role, acting to allow TraD protein levels to increase only in the absence of iron. To better understand type IV secretion system regulation during infection, we examined transcriptomic data from active urethral infection samples from five men. These data demonstrated differential expression of 20 of 21 type IV secretion system genes during infection, indicating upregulation of genes necessary for DNA secretion during host infection.

microbiology↗

bioRxiv2017

Evolutionary Genetics of a Disease Susceptibility Locus in CDHR3

Selective pressures imposed by pathogens have varied among human populations throughout their evolution, leading to marked inter-population differences at some genes mediating susceptibility to infectious and immune-related diseases. A common polymorphism resulting in a C529 versus T529 change in the Cadherin-Related Family Member 3 (CDHR3) receptor is associated with rhinovirus-C (RV-C) susceptibility and severe childhood asthma. Given the morbidity and mortality associated with RV-C dependent respiratory infections and asthma, we hypothesized that the protective variant has been under selection in the human population. Supporting this idea, a recent cross-species outbreak of RV-C among chimpanzees in Uganda, which carry the ancestral risk allele at this position, resulted in a mortality rate of 8.9%. Using publicly available genomic data, we sought to determine the evolutionary history and role of selection acting on this infectious disease susceptibility locus. The protective variant is the derived allele and is found at high frequency worldwide, with the lowest relative frequency in African populations and highest in East Asian populations. There is minimal population structure among haplotypes, and we detect genomic signatures consistent with a rapid increase in frequency of the protective allele across all human populations. However, given strong evidence that the protective allele arose in anatomically modern humans prior to their migrations out of Africa and that the allele has not fixed in any population, the patterns observed here are not consistent with a classical selective sweep. We hypothesize that patterns may indicate frequency-dependent selection worldwide. Irrespective of the mode of selection, our analyses show the derived allele has been subject to selection in recent human evolution.

genetics↗