Biology subjects

Bischoff, E.

Publications and source records attributed to Bischoff, E..

5 recordsLinked to original sources

bioRxiv2021

Protein abundance and folding rather than the redox state of Kelch13 determine the artemisinin susceptibility of Plasmodium falciparum

Decreased susceptibilities of Plasmodium falciparum towards the endoperoxide antimalarial artemisinin are linked to mutations of residue C580 of Kelch13, which is the homologue of the redox sensor Keap1 in vertebrates. Here, we addressed whether mutations alter the artemisinin susceptibility by modifying the redox properties of Kelch13 or by compromising its native fold or abundance. Using selection-linked integration and the glmS ribozyme, efficient down-regulation of Kelch13 resulted in ring-stage survival rates around 40%. While the loss of a potential disulfide bond between residues C580 and C532 had no effect on the artemisinin suceptibility, the thiol group of C473 could not be replaced. We also established a protocol for the production of recombinant Kelch13. In contrast to cysteine-to-serine replacements, common field mutations resulted in misfolded and insoluble protein. In summary, not the redox properties but impaired folding of Kelch13, resulting in a decreased Kelch13 abundance, is the central parameter for mutant selection.

biochemistry↗

bioRxiv2020

Anopheles gambiae maternal age and parous state control offspring susceptibility to Plasmodium falciparum

Maternal effects have been reported in many organisms whereby exposure to environmental stress, either toxics or pathogens will impact on progeny response to these stresses. Here we show that Anopheles gambiae susceptibility to Plasmodium falciparum is dependent upon maternal effects driven by females not previously exposed to the parasite. The maternal effect involved both mother age and reproductive state. Offspring of old females or from a 4th gonotrophic cycle are more susceptible than offspring from young females. These maternal effects also contribute to overall better fitness of the offspring. As mosquito population age structure contributes heavily shaping malaria transmission, consequences of this novel finding should be taken into account in further strategies for controlling malaria transmission.

genetics↗

bioRxiv2019

The APL1 immune factor is encoded by a single ancestral gene in most Anopheles species and expanded to three paralogs with distinct function in the Anopheles gambiae complex

BackgroundThe recent reference genome assembly and annotation of the Asian malaria vector Anopheles stephensi revealed only one gene encoding the leucine-rich repeat immune factor APL1, while in Anopheles gambiae and sibling Anopheles coluzzii, APL1 factors are encoded by a family of three paralogs. The phylogeny and biological function of the unique APL1 gene in A. stephensi have not yet been specifically examined.\n\nMethodsThe APL1 locus was manually sequenced to confirm the computationally predicted single APL1 gene in A. stephensi, and APL1 evolution within Anopheles was explored by phylogenomic analysis. The single or paralogous APL1 genes were silenced in A. stephensi and A. coluzzii, respectively, followed by mosquito survival analysis, experimental infection with Plasmodium, and expression analysis.\n\nResultsAPL1 is present as a single ancestral gene in most Anopheles including A. stephensi, but has expanded to three paralogs in an African lineage that includes only the Gambiae species complex and Anopheles christyi. Silencing of the unique APL1 copy in A. stephensi results in significant mosquito mortality. Elevated mortality of APL1-depleted A. stephensi is rescued by antibiotic treatment, suggesting that bacteria are the cause of mortality, and that the unique APL1 gene is essential for host survival. Successful Plasmodium development in A. stephensi depends upon APL1 activity for protection from high host mortality, probably caused by exposure to enteric bacteria when parasites cross the midgut epithelial barrier. In contrast, silencing of all three APL1 paralogs in A. coluzzii does not result in elevated mortality, either with or without Plasmodium infection. Expression of the single APL1 gene is regulated by both the Imd and Toll immune pathways, while control by the two pathways is subdivided to different paralogs in the expanded APL1 locus.\n\nConclusionsAPL1 underwent neofunctionalization with both loss and gain of functions concomitant with expansion from a single ancestral gene to three paralogs in one lineage of African Anopheles. The evolution of an expanded APL1 gene family could be a factor contributing to the exceptional levels of malaria transmission mediated by human-feeding members of the Gambiae complex in Africa.

genetics↗

bioRxiv2019

Influence of genetic polymorphism on transcriptional enhancer activity in the malaria vector Anopheles coluzzii

Enhancers are cis-regulatory elements that control most of the developmental and spatial gene expression in eukaryotes. Genetic variation of enhancer sequences is known to influence phenotypes, but the effect of enhancer variation upon enhancer functional activity and downstream phenotypes has barely been examined in any species. In the African malaria vector, Anopheles coluzzii, we identified a pilot set of candidate enhancers in the proximity of genes relevant for immunity, insecticide resistance, and development. The candidate enhancers were functionally validated using luciferase reporter assays, and their activity was found to be essentially independent of their physical orientation, a typical property of enhancers. All of the enhancer intervals segregated genetically polymorphic alleles, which displayed significantly different levels of functional activity, and inactive null alleles were also observed. Deletion mutagenesis and functional testing revealed a modular structure of positive and negative regulatory elements within the tested enhancers. The enhancer alleles carry genetic polymorphisms that also segregate in wild A. coluzzii populations in West Africa, indicating that enhancer variants with likely phenotypic consequences are frequent in nature. These results demonstrate the feasibility of screening for naturally polymorphic A. coluzzii enhancers that underlie important aspects of malaria transmission and vector biology.

genetics↗

bioRxiv2018

Evolution of sexually-transferred steroids in Anopheles mosquitoes

Human malaria, which remains a major public health problem, is transmitted by a subset of Anopheles mosquitoes belonging to only three out of eight subgenera: Anopheles, Cellia and Nyssorhynchus. Unlike almost every other insect species, it was shown that males of some Anopheles species produce and transfer steroid hormones to females during copulation and that this transfer mediates reproductive changes. Steroids are consequently seen as a potential target for malaria vector control. Here, we analysed the evolution of sexually-transferred steroids and their effects on female reproductive traits across Anopheles by using a set of 16 mosquito species (5 Anopheles, 8 Cellia, and 3 Nyssorhynchus), including malaria vector and non-vector species. We show that male steroid production and transfer are specific to the Cellia subgenus and that there is no correlation between mating-induced effects in females and sexually-transferred steroids. In the light of our results, male steroid production, transfer and post-mating effects in females do not correlate with their ability to transmit human malaria, which overturns the suggestion from previous studies and suggests that manipulation of steroid-response pathways in the field should be considered with caution in order to benefit malaria vector control strategies.

evolutionary biology↗