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Author: Donna Huber

Genetic crosses within and between species of Cryptosporidium

Donna Huber on January 2, 2024

Figure 1 PheRS can be used as a selection marker for stable transgenesis.
PheRS can be used as a selection marker for stable transgenesis.

Parasites and their hosts are engaged in reciprocal coevolution that balances competing mechanisms of virulence, resistance, and evasion. This often leads to host specificity, but genomic reassortment between different strains can enable parasites to jump host barriers and conquer new niches. In the apicomplexan parasite Cryptosporidium, genetic exchange has been hypothesized to play a prominent role in adaptation to humans. The sexual lifecycle of the parasite provides a potential mechanism for such exchange; however, the boundaries of Cryptosporidium sex are currently undefined. To explore this experimentally, we established a model for genetic crosses. Drug resistance was engineered using a mutated phenylalanyl tRNA synthetase gene and marking strains with this and the previously used Neo transgene enabled selection of recombinant progeny. This is highly efficient, and genomic recombination is evident and can be continuously monitored in real time by drug resistance, flow cytometry, and PCR mapping. Using this approach, multiple loci can now be modified with ease. We demonstrate that essential genes can be ablated by crossing a Cre recombinase driver strain with floxed strains. We further find that genetic crosses are also feasible between species. Crossing Cryptosporidium parvum, a parasite of cattle and humans, and Cryptosporidium tyzzeri a mouse parasite resulted in progeny with a recombinant genome derived from both species that continues to vigorously replicate sexually. These experiments have important fundamental and translational implications for the evolution of Cryptosporidium and open the door to reverse- and forward-genetic analysis of parasite biology and host specificity.

Sebastian Shaw, Ian S Cohn, Rodrigo P Baptista, Guoqin Xia, Bruno Melillo, Fiifi Agyabeng-Dadzie, Jessica C Kissinger, Boris Striepen. Proc Natl Acad Sci USA. 2024 Jan 2;121(1):e2313210120. doi: 10.1073/pnas.2313210120.

Aptamer-Based Imaging of Polyisoprenoids in the Malaria Parasite

Donna Huber on December 28, 2023

Figure 1. Schemes of the positive and negative selection cycles are illustrated.
Figure 1. Schemes of the positive and negative selection cycles are illustrated.

 

Dolichols are isoprenoid end-products of the mevalonate and 2C-methyl-D-erythritol-4-phosphate pathways. The synthesis of dolichols is initiated with the addition of several molecules of isopentenyl diphosphate to farnesyl diphosphate. This reaction is catalyzed by a cis-prenyltransferase and leads to the formation of polyprenyl diphosphate. Subsequent steps involve the dephosphorylation and reduction of the α-isoprene unit by a polyprenol reductase, resulting in the generation of dolichol. The size of the dolichol varies, depending on the number of isoprene units incorporated. In eukaryotes, dolichols are synthesized as a mixture of four or more different lengths. Their biosynthesis is predicted to occur in the endoplasmic reticulum, where dolichols play an essential role in protein glycosylation. In this study, we have developed a selection of aptamers targeting dolichols and enhanced their specificity by incorporating fatty acids for negative selection. One aptamer showed high enrichment and specificity for linear polyisoprenoids containing at least one oxygen atom, such as an alcohol or aldehyde, in the α-isoprene unit. The selected aptamer proved to be a valuable tool for the subcellular localization of polyisoprenoids in the malaria parasite. To the best of our knowledge, this is the first time that polyisoprenoids have been localized within a cell using aptamer-based imaging techniques.

Flavia M Zimbres, Emilio F Merino, Grant J Butschek, Joshua H Butler, Frédéric Ducongé, Maria B Cassera. Molecules. 2023 Dec 28;29(1):178. doi: 10.3390/molecules29010178.

Inherently Reduced Expression of ASC Restricts Caspase-1 Processing in Hepatocytes and Promotes Plasmodium Infection

Donna Huber on December 27, 2023

Fig. 1 Inherently reduced expression of pro–caspase-1 and ASC in hepatocytes.
Inherently reduced expression of pro–caspase-1 and ASC in hepatocytes.

 

Inflammasome-mediated caspase-1 activation facilitates innate immune control of Plasmodium in the liver, thereby limiting the incidence and severity of clinical malaria. However, caspase-1 processing occurs incompletely in both mouse and human hepatocytes and precludes the generation of mature IL-1β or IL-18, unlike in other cells. Why this is so or how it impacts Plasmodium control in the liver has remained unknown. We show that an inherently reduced expression of the inflammasome adaptor molecule apoptosis-associated specklike protein containing CARD (ASC) is responsible for the incomplete proteolytic processing of caspase-1 in murine hepatocytes. Transgenically enhancing ASC expression in hepatocytes enabled complete caspase-1 processing, enhanced pyroptotic cell death, maturation of the proinflammatory cytokines IL-1β and IL-18 that was otherwise absent, and better overall control of Plasmodium infection in the liver of mice. This, however, impeded the protection offered by live attenuated antimalarial vaccination. Tempering ASC expression in mouse macrophages, on the other hand, resulted in incomplete processing of caspase-1. Our work shows how caspase-1 activation and function in host cells are fundamentally defined by ASC expression and offers a potential new pathway to create better disease and vaccination outcomes by modifying the latter.

Camila Marques-da-Silva, Clyde Schmidt-Silva, Rodrigo P Baptista, Samarchith P Kurup. J Immunol. 2023 Dec 27:ji2300440. doi: 10.4049/jimmunol.2300440. Online ahead of print.

On the origin and evolution of the mosquito male-determining factor Nix

Donna Huber on December 21, 2023

Background and workflow.

The mosquito family Culicidae is divided into two subfamilies named the Culicinae and Anophelinae. Nix, the dominant male-determining factor, has only been found in the culicines Aedes aegypti and Ae. albopictus, two important arboviral vectors that belong to the subgenus Stegomyia. Here we performed sex-specific whole-genome sequencing and RNAseq of divergent mosquito species and explored additional male-inclusive datasets to investigate the distribution of Nix. Except for the Culex genus, Nix homologs were found in all species surveyed from the Culicinae subfamily, including 12 additional species from three highly divergent tribes comprising 4 genera, suggesting Nix originated at least 133-165 MYA. Heterologous expression of one of three divergent Nix ORFs in Ae. aegypti resulted in partial masculinization of genetic females as evidenced by morphology and doublesex splicing. Phylogenetic analysis suggests Nix is related to femaleless (fle), a recently described intermediate sex-determining factor found exclusively in anopheline mosquitoes. Nix from all species has a conserved structure, including three RNA-recognition motifs (RRMs), as does fle. However, Nix has evolved at a much faster rate than fle. The RRM3 of both Nix and fle are distantly related to the single RRM of a widely distributed and conserved splicing factor transformer-2 (tra2). RRM3-based phylogenetic analysis suggests this domain in Nix and fle may have evolved from tra2 or a tra2-related gene in a common ancestor of mosquitoes. Our results provide insights into the evolution of sex-determination in mosquitoes and will inform broad applications of mosquito-control strategies based on manipulating sex ratios towards the non-biting males.

James K Biedler, Azadeh Aryan, Yumin Qi, Aihua Wang, Ellen O Martinson, Daniel A Hartman, Fan Yang, Atashi Sharma, Katherine S Morton, Mark Potters, Chujia Chen, Stephen L Dobson, Gregory D Ebel, Rebekah C Kading, Sally Paulson, Rui-De Xue, Michael R Strand, Zhijian Tu. Mol Biol Evol. 2023 Dec 21:msad276. doi: 10.1093/molbev/msad276. Online ahead of print.

Atlas of Plasmodium falciparum intraerythrocytic development using expansion microscopy

Donna Huber on December 18, 2023

Ultrastructural expansion microscopy (U-ExM) workflow and summary of parasite structures imaged in this study.
Ultrastructural expansion microscopy (U-ExM) workflow and summary of parasite structures imaged in this study.

Apicomplexan parasites exhibit tremendous diversity in much of their fundamental cell biology, but study of these organisms using light microscopy is often hindered by their small size. Ultrastructural expansion microscopy (U-ExM) is a microscopy preparation method that physically expands the sample by ~4.5×. Here, we apply U-ExM to the human malaria parasite Plasmodium falciparum during the asexual blood stage of its lifecycle to understand how this parasite is organized in three dimensions. Using a combination of dye-conjugated reagents and immunostaining, we have cataloged 13 different P. falciparum structures or organelles across the intraerythrocytic development of this parasite and made multiple observations about fundamental parasite cell biology. We describe that the outer centriolar plaque and its associated proteins anchor the nucleus to the parasite plasma membrane during mitosis. Furthermore, the rhoptries, Golgi, basal complex, and inner membrane complex, which form around this anchoring site while nuclei are still dividing, are concurrently segregated and maintain an association to the outer centriolar plaque until the start of segmentation. We also show that the mitochondrion and apicoplast undergo sequential fission events while maintaining an association with the outer centriolar plaque during cytokinesis. Collectively, this study represents the most detailed ultrastructural analysis of P. falciparum during its intraerythrocytic development to date and sheds light on multiple poorly understood aspects of its organelle biogenesis and fundamental cell biology.

Benjamin Liffner, Ana Karla Cepeda Diaz, James Blauwkamp, David Anaguano, Sonja Frolich, Vasant Muralidharan, Danny W Wilson, Jeffrey D Dvorin, Sabrina Absalon. Elife. 2023 Dec 18:12:RP88088. doi: 10.7554/eLife.88088.

Advances in the cellular biology, biochemistry, and molecular biology of acidocalcisomes

Donna Huber on December 15, 2023

Fig 1 Ultrastructure of acidocalcisomes
Fig 1 Ultrastructure of acidocalcisomes.

Acidocalcisomes are organelles conserved during evolution and closely related to the so-called volutin granules of bacteria and archaea, to the acidocalcisome-like vacuoles of yeasts, and to the lysosome-related organelles of animal species. All these organelles have in common their acidity and high content of polyphosphate and calcium. They are characterized by a variety of functions from storage of phosphorus and calcium to roles in Ca2+ signaling, osmoregulation, blood coagulation, and inflammation. They interact with other organelles through membrane contact sites or by fusion, and have several enzymes, pumps, transporters, and channels.

Roberto Docampo. Microbiol Mol Biol Rev. 2023 Dec 15:e0004223. doi: 10.1128/mmbr.00042-23.

Optimized strategy for real-time qPCR detection of Onchocerca volvulus DNA in pooled Simulium sp. blackfly vectors

Donna Huber on December 14, 2023

Fig 1. Workflow for the selection of the optimal qPCR assay.
Fig 1. Workflow for the selection of the optimal qPCR assay.

 

Background: Onchocerca volvulus is a filarial parasite that is a major cause of dermatitis and blindness in endemic regions primarily in sub-Saharan Africa. Widespread efforts to control the disease caused by O. volvulus infection (onchocerciasis) began in 1974 and in recent years, following successful elimination of transmission in much of the Americas, the focus of efforts in Africa has moved from control to the more challenging goal of elimination of transmission in all endemic countries. Mass drug administration (MDA) with ivermectin has reached more than 150 million people and elimination of transmission has been confirmed in four South American countries, with at least two African countries having now stopped MDA as they approach verification of elimination. It is essential that accurate data for active transmission are used to assist in making the critical decision to stop MDA, since missing low levels of transmission and infection can lead to continued spread or recrudescence of the disease.

Methodology/principal findings: Current World Health Organization guidelines for MDA stopping decisions and post-treatment surveillance include screening pools of the Simulium blackfly vector for the presence of O. volvulus larvae using a PCR-ELISA-based molecular technique. In this study, we address the potential of an updated, practical, standardized molecular diagnostic tool with increased sensitivity and species-specificity by comparing several candidate qPCR assays. When paired with heat-stable reagents, a qPCR assay with a mitochondrial DNA target (OvND5) was found to be more sensitive and species-specific than an O150 qPCR, which targets a non-protein coding repetitive DNA sequence. The OvND5 assay detected 19/20 pools of 100 blackfly heads spiked with a single L3, compared to 16/20 for the O150 qPCR assay.

Conclusions/significance: Given the improved sensitivity, species-specificity and resistance to PCR inhibitors, we identified OvND5 as the optimal target for field sample detection. All reagents for this assay can be shipped at room temperature with no loss of activity. The qPCR protocol we propose is also simpler, faster, and more cost-effective than the current end-point molecular assays.

 

Mary Doherty, Jessica R Grant, Nils Pilotte, Sasisekhar Bennuru, Kerstin Fischer, Peter U Fischer, Sara Lustigman, Thomas B Nutman, Kenneth Pfarr, Achim Hoerauf, Thomas R Unnasch, Hassan K Hassan, Samuel Wanji, Patrick J Lammie, Eric Ottesen, Charles Mackenzie, Steven A Williams. PLoS Negl Trop Dis. 2023 Dec 14;17(12):e0011815. doi: 10.1371/journal.pntd.0011815.

Trypanosoma cruzi heme responsive gene (TcHRG) plays a central role in orchestrating heme uptake in epimastigotes

Donna Huber on December 13, 2023

Trypanosoma cruzi, a heme auxotrophic parasite, can control intracellular heme content by modulating heme responsive gene (TcHRG) expression when a free heme source is added to an axenic culture. Herein, we explored the role of TcHRG protein in regulating the uptake of heme derived from hemoglobin in epimastigotes. We demonstrate that the endogenous TcHRG (protein and mRNA) responded similarly to bound (hemoglobin) and free (hemin) heme. Endogenous TcHRG was found in the flagellar pocket boundaries and partially overlapping with the mitochondrion. On the other hand, endocytic null parasites were able to develop and exhibited a similar heme content compared to wild type when fed with hemoglobin, indicating that endocytosis is not the main entrance pathway for hemoglobin-derived heme in this parasite. Moreover, the overexpression of TcHRG led to an increase in heme content when hemoglobin was used as the heme source. Taken together, these results suggest that the uptake of hemoglobin-derived heme likely occurs through extracellular proteolysis of hemoglobin via the flagellar pocket, and this process is governed by TcHRG. In sum, T. cruzi epimastigotes control heme homeostasis by modulating TcHRG expression independently of the available source of heme.

Evelyn Tevere, Cecilia Beatriz Di Capua, Nathan Michael Chasen, Ronald Drew Etheridge, Julia Alejandra Cricco. FEBS J. 2023 Dec 13. doi: 10.1111/febs.17030.

Increased environmental microbial diversity reduces the disease risk of a mosquitocidal pathogen

Donna Huber on December 7, 2023

Fig 6 Ch_R13E2-SpR systemically infects A. aegypti larvae.
Fig 6 Ch_R13E2-SpR systemically infects A. aegypti larvae.

The host-specific microbiotas of animals can both reduce and increase disease risks from pathogens. In contrast, how environmental microbial communities affect pathogens is largely unexplored. Aquatic habitats are of interest because water enables environmental microbes to readily interact with animal pathogens. Here, we focused on mosquitoes, which are important disease vectors as terrestrial adults but are strictly aquatic as larvae. We identified a pathogen of mosquito larvae from the field as a strain of Chromobacterium haemolyticum. Comparative genomic analyses and functional assays indicate this strain and other Chromobacterium are mosquitocidal but are also opportunistic pathogens of other animals. We also identify a critical role for diversity of the environmental microbiota in disease risk. Our study characterizes both the virulence mechanisms of a pathogen and the role of the environmental microbiota in disease risk to an aquatic animal of significant importance to human health.

Zhiwei Kang, Vincent G Martinson, Yin Wang, Kerri L Coon, Luca Valzania, Michael R Strand. mBio. 2023 Dec 6:e0272623. doi: 10.1128/mbio.02726-23.