Biology subjects

Button-Simons, K. A.

Publications and source records attributed to Button-Simons, K. A..

6 recordsLinked to original sources

bioRxiv2023

Using a P. falciparum genetic cross to dissect the relative contributions of pfcrt and plasmepsin II/III to piperaquine response-related traits

Piperaquine (PPQ) is widely used in combination with dihydroartemisinin (DHA) as a first-line treatment against malaria parasites. Multiple genetic drivers of PPQ resistance have been reported, including mutations in the Plasmodium falciparum chloroquine resistance transporter (pfcrt) and increased copies of plasmepsin II/III (pm2/3). We generated a cross between a Cambodia-derived multi-drug resistant KEL1/PLA1 lineage isolate (KH004) and a drug susceptible parasite isolated in Malawi (Mal31). Mal31 harbors a wild-type (3D7-like) pfcrt allele and a single copy of pm2/3, while KH004 has a chloroquine-resistant (Dd2-like) pfcrt allele with an additional G367C substitution and four copies of pm2/3. We recovered 104 unique recombinant progeny and examined a targeted set of progeny representing all possible combinations of variants at pfcrt and pm2/3 for detailed analysis of competitive fitness and a range of PPQ susceptibility phenotypes, including PPQ survival assay (PSA), area under the dose-response curve (AUC), and a limited point IC50 (LP-IC50). We find that inheritance of the KH004 pfcrt allele is required for PPQ resistance, whereas copy number variation in pm2/3 further enhances resistance but does not confer resistance in the absence of PPQ-R-associated mutations in pfcrt. Deeper investigation of genotype-phenotype relationships demonstrates that progeny clones from experimental crosses can be used to understand the relative contributions of pfcrt, pm2/3, and parasite genetic background, to a range of PPQ-related traits and confirm the critical role of the PfCRT G367C substitution in PPQ resistance. ImportanceResistance to PPQ used in combination with DHA has emerged in Cambodia and threatens to spread to other malaria-endemic regions. Understanding the causal mutations of drug resistance and their impact on parasite fitness is critical for surveillance and intervention, and can also reveal new avenues to limiting the evolution and spread of drug resistance. An experimental genetic cross is a powerful tool for pinpointing the genetic determinants of key drug resistance and fitness phenotypes and have the distinct advantage of assaying the effects of naturally evolved genetic variation. Our study was significantly strengthened because the full a range of copies of KH004 pm2/3 was inherited among the progeny clones, allowing us to directly test the role of pm2/3 copy number on resistance-related phenotypes in the context of a unique pfcrt allele. Our multi-gene model suggests an important role for both loci in the evolution of this ACT resistant parasite lineage.

genomics↗

bioRxiv2023

Enhancing gene co-expression network inference for the malaria parasite Plasmodium falciparum

BackgroundMalaria results in more than 550,000 deaths each year due to drug resistance in the most lethal Plasmodium (P.) species P. falciparum. A full P. falciparum genome was published in 2002, yet 44.6% of its genes have unknown functions. Improving functional annotation of genes is important for identifying drug targets and understanding the evolution of drug resistance. ResultsGenes function by interacting with one another. So, analyzing gene co-expression networks can enhance functional annotations and prioritize genes for wet lab validation. Earlier efforts to build gene co-expression networks in P. falciparum have been limited to a single network inference method or gaining biological understanding for only a single gene and its interacting partners. Here, we explore multiple inference methods and aim to systematically predict functional annotations for all P. falciparum genes. We evaluate each inferred network based on how well it predicts existing gene-Gene Ontology (GO) term annotations using network clustering and leave-one-out cross-validation. We assess overlaps of the different networks edges (gene co-expression relationships) as well as predicted functional knowledge. The networks edges are overall complementary: 47%-85% of all edges are unique to each network. In terms of accuracy of predicting gene functional annotations, all networks yield relatively high precision (as high as 87% for the network inferred using mutual information), but the highest recall reached is below 15%. All networks having low recall means that none of them capture a large amount of all existing gene-GO term annotations. In fact, their annotation predictions are highly complementary, with the largest pairwise overlap of only 27%. We provide ranked lists of inferred gene-gene interactions and predicted gene-GO term annotations for future use and wet lab validation by the malaria community. ConclusionsThe different networks seem to capture different aspects of the P. falciparum biology in terms of both inferred interactions and predicted gene functional annotations. Thus, relying on a single network inference method should be avoided when possible. Supplementary dataAttached. Availability and implementationAll data and code are available at https://nd.edu/~cone/pfalGCEN/. Contacttmilenko@nd.edu

systems biology↗

bioRxiv2022

The amino acid transporter pfaat1 modulates chloroquine resistance and fitness in malaria parasites

Malaria parasites break down host hemoglobin into peptides and amino acids in the digestive vacuole for export to the parasite cytoplasm for growth: interrupting this process is central to the mode of action of several antimalarial drugs. Mutations in the chloroquine (CQ) resistance transporter, pfcrt, located in the digestive vacuole membrane, confer CQ resistance in Plasmodium falciparum, but typically affect parasite fitness. However, the role of other parasite loci in the evolution of CQ resistance is unclear. Here we use a combination of population genomics, genetic crosses and gene editing to demonstrate that a second vacuolar transporter plays a key role in both resistance and compensatory evolution. Longitudinal genomic analyses of the Gambian parasites revealed temporal signatures of selection on an amino acid transporter (pfaat1) S258L variant which increased from 0-87% in frequency between 1984 and 2014 in parallel with pfcrt1 K76T. Parasite genetic crosses then identified a chromosome 6 quantitative trait locus containing pfaat1 that is selected by CQ treatment. Gene editing demonstrated that pfaat1 S258L potentiates CQ-resistance but at a cost of reduced fitness, while pfaat1 F313S, a common Southeast Asian polymorphism, reduces CQ-resistance while restoring fitness. Our analyses reveal hidden complexity in CQ-resistance evolution, suggesting that pfaat1 may underlie regional differences in the dynamics of resistance evolution, and modulate parasite resistance or fitness by manipulating the balance between both amino acid and drug transport.

genomics↗

bioRxiv2021

Optimizing bulk segregant analysis of drug resistance using Plasmodium falciparum genetic crosses conducted in humanized mice

BackgroundClassical genetic crosses in malaria parasites involve isolation, genotyping, and phenotyping of multiple progeny parasites, which is time consuming and laborious. Bulk segregant analysis (BSA) offers a powerful and efficient alternative to identify loci underlying complex traits in the human malaria parasite, Plasmodium falciparum. MethodsWe have used BSA, which combines genetic crosses using humanized mice with pooled sequencing of progeny populations to measure changes in allele frequency following selection with antimalarial drugs. We used dihydroartemisinin (DHA) drug selection in two genetic crosses (Mal31xKH004 and NF54xNHP1337). We specifically investigated how synchronization, cryopreservation, and the drug selection regimen of progeny pools impacted the success of BSA experiments. FindingsWe detected a strong and repeatable quantitative trait locus (QTL) at chr13 kelch13 locus in both crosses, but did not detect QTLs at ferredoxin (fd), the apicoplast ribosomal protein S10 (arps10), multidrug resistance protein 2 (mdr2). QTLs were detected using synchronized, but not unsynchronized pools, consistent with the stage-specific action of DHA. We also successfully applied BSA to cryopreserved progeny pools. InterpretationOur results provide proof-of-principal of the utility of BSA for rapid, robust genetic mapping of drug resistance loci. Use of cryopreserved progeny pools expands the utility of BSA because we can conduct experiments using archived progeny pools from previous genetic crosses. BSA provides a powerful approach that complements traditional QTL methods for investigating the genetic architecture of resistance to antimalarials, and to reveal new or accessory loci contributing to artemisinin resistance. FundingNational Institutes of Health (NIH); Wellcome trust. O_TEXTBOXResearch in contextO_ST_ABSEvidence before this studyC_ST_ABSGenetic crosses have been immensely successful for determining the genetic basis of drug resistance in malaria parasites, but require laborious cloning, characterization of drug resistance and genome-wide genotyping of individual progeny. This is a major limitation given that genetic crosses can now be conducted efficiently using humanized mice, rather than chimpanzees. Bulk segregant analysis (BSA) provides an attractive alternative approach because (i) large numbers of uncloned recombinant progeny can be analyzed, increasing statistical power (ii) phenotyping is not required, because we identify QTLs by treatment of progeny bulks, and identifying genome regions that show skews in allele frequency after treatment (iii) genome sequencing of bulk samples provides a rapid, accurate readout of genome-wide allele frequencies. This approach has been effectively leveraged in yeast, rodent malaria and several model organisms. Added value of this studyHere we validate and optimize this approach for P. falciparum genetic crosses, focusing on resistance to dihydroartemisin (DHA) a central component of the first-line antimalarial combination. Mutations in kelch13 are known to confer resistance to DHA, but several additional candidate loci have also been suggested to contribute. Our results confirm involvement of kelch13, but did not identify linkage with other putative candidate loci. We optimized methodology, showing that synchronization is critical, and that BSA can be successfully applied to cryopreserved progeny pools. Implications of all the available evidenceBSA combined with recent advances in rapidly generating genetic crosses provides a powerful approach to investigate the genetic basis of drug resistance in P. falciparum. C_TEXTBOX

genomics↗

bioRxiv2019

Surprising variation in the outcome of two malaria genetic crosses using humanized mice: implications for genetic mapping and malaria biology

Genetic crosses are most powerful for linkage analysis when progeny numbers are high, when parental alleles segregate evenly and, for hermaphroditic organisms, when numbers of inbred progeny are minimized. We previously developed a novel genetic crossing platform for the human malaria parasite Plasmodium falciparum, an obligately sexual, hermaphroditic protozoan, using mice carrying human hepatocytes (the human liver-chimeric FRG NOD huHep mouse) as the vertebrate host. Here we examine the statistical power of two different genetic crosses - (1) between a laboratory parasite (NF54) of African origin and a patient-derived Asian parasite, and (2) between two sympatric patient-derived Asian parasites. We generated >140 unique recombinant clones over a 12-month period from the four parental genotypes, doubling the number of unique recombinant progeny generated in the previous 30 years. Both crosses show bi-parental inheritance of plastid markers amongst recombinant progeny, in contrast to previous crosses (conducted using chimpanzee hosts) which carried single dominant plastid genotypes. Both crosses show distinctive segregation patterns. The allopatric African/Asian cross has minimal levels of inbreeding (2% of clonal progeny are inbred) and extreme skews in marker segregation, while in the sympatric Asian cross, inbred progeny predominate (66% of clonal progeny are inbred) and parental alleles segregate evenly. Using simulations, we demonstrate that these progeny arrays (particularly the sympatric Asian cross) have excellent power to map large-effect mutations to a 31 kb interval and can capture complex, epistatic interactions that were far beyond the capacity of previous malaria crosses to detect. The extreme segregation distortion in the allopatric African/Asian cross erodes power to detect linkage in several genome regions, but the repeatable distortions observed offer promising alternative approaches to identifying genes underlying traits of interest. These crosses show surprising variation in marker segregation, nevertheless, the increased progeny numbers improve our ability to rapidly map biomedically important parasite traits. Author SummaryUnderstanding how genome mutations contribute to newly emerging drug resistance in parasites like Plasmodium falciparum is important to monitor the spread of drug resistance. This scenario has been playing out in Southeast Asia with the emergence and spread of artemisinin resistance. Here we show that new P. falciparum genetic crosses, using mice carrying human liver cells and infused with human red blood cells (the human liver-chimeric FRG NOD huHep/huRBC mouse), provide an important new tool for understanding complex interactions underlying drug resistance phenotypes. We report two new genetic maps with 84 and 60 unique recombinant progeny, which doubles the number of progeny available from 4 previous P. falciparum genetic crosses. Through extensive simulations we show that with 84 progeny we can find association for a gene that controls only 20% of the variation in a phenotype. We also show that a cross generated from Southeast Asian parasites collected from the same geographic region have unique characteristics not previously observed in P. falciparum genetic crosses. This Southeast Asian cross exhibits even segregation across the genome, unbiased inheritance of mitochondria and apicoplast and higher levels of inbreeding than previously observed.

genetics↗

bioRxiv2019

The extended recovery ring stage survival assay provides superior prediction of patient clearance half life and increases throughput

BackgroundTracking and understanding artemisinin resistance is key for preventing global setbacks in malaria eradication efforts. The ring-stage survival assay (RSA) is the current gold standard for in vitro artemisinin resistance phenotyping. However, the RSA has several drawbacks: it is relatively low throughput, has high variance due to microscopy readout, and correlates poorly with the current benchmark for in vivo resistance, patient clearance half-life post-artemisinin treatment. Here a modified RSA is presented, the extended Recovery Ring-stage Survival Assay (eRRSA), using 15 cloned patient isolates from Southeast Asia with a range of patient clearance half-lives, including parasite isolates with and without kelch13 mutations. MethodsP. falciparum cultures were synchronized with single layer Percoll during the schizont stage of the erythrocytic cycle. Cultures were left to reinvade to early ring-stage and parasitemia was quantified using flow cytometry. Cultures were diluted to 2% hematocrit and 0.5% parasitemia in a 96-well plate to start the assay, allowing for increased throughput and decreased variability between biological replicates. Parasites were treated with 700nM of dihydroartemisinin or an equivalent amount of dimethyl sulfoxide (DMSO) for 6 h, washed three times in drug-free media, and incubated for 66 or 114 h, when samples were collected and frozen for PCR amplification. A SYBR Green-based quantitative PCR method was used to quantify the fold-change between treated and untreated samples. Results15 cloned patient isolates from Southeast Asia with a range of patient clearance half-lives were assayed using the eRRSA. Due to the large number of pyknotic and dying parasites at 66 h post-exposure (72 h sample), parasites were grown for an additional cell cycle (114 h post-exposure, 120 h sample), which drastically improved correlation with patient clearance half-life compared to the 66 h post-exposure sample. A Spearman correlation of 0.8393 between fold change and patient clearance half-life was identified in these 15 isolates from Southeast Asia, which is the strongest correlation reported to date. ConclusionseRRSA drastically increases the efficiency and accuracy of in vitro artemisinin resistance phenotyping compared to the traditional RSA, which paves the way for extensive in vitro phenotyping of hundreds of artemisinin resistant parasites.

microbiology↗