Biology subjects

Ralston, K. S.

Publications and source records attributed to Ralston, K. S..

7 recordsLinked to original sources

bioRxiv2026

CRISPR/Cas9 knockout and editing of the major cysteine protease in Entamoeba histolytica

Entamoeba histolytica is the cause of amoebiasis, a diarrheal infection that is a significant source of morbidity and mortality. Despite its importance to human health, the basic mechanism of disease is poorly understood. E. histolytica is dramatically understudied, even in comparison to other understudied parasites, due to challenging features of its genome and the relative paucity of genetic tools. A major limitation is the historical lack of gene knockouts or manipulation of the endogenous genome. While CRISPR/Cas9 has led to major advances in the tractability of numerous parasites, until recently, it was not applied in E. histolytica, except for the demonstration of editing of an episomal plasmid. In this study, we further developed CRISPR/Cas9 and demonstrated the successful targeting of the endogenous cysteine protease 5 (CP5) gene, a major virulence factor. Further, we demonstrated successful CRISPR/Cas9-based editing of this locus, which represents the very first successful editing of the endogenous genome. In the course of these approaches, we developed the viral skip peptide approach as well as a suite of endogenous promoters to drive tunable levels of gene expression. We also performed the most extensive empirical testing of nuclear localization signals in E. histolytica that has been done. Thus, this work demonstrates effective CRISPR/Cas9-based manipulation of the endogenous genome, together with significant advances to the overall genetic toolkit that extend beyond CRISPR/Cas9. These great improvements in the tractability of E. histolytica thus set the stage for future studies to better define its virulence.

microbiology↗

bioRxiv2026

Human cell F-actin density differentially influences trogocytosis and phagocytosis by Entamoeba histolytica

Entamoeba histolytica is a parasitic amoeba and the cause amoebiasis, a common but understudied human diarrheal disease. E. histolytica trophozoites ("amoebae") kill human cells through a process of cell-nibbling called trogocytosis (trogo-: nibble) that contributes to tissue damage. Amoebae can also perform phagocytosis, in which entire human cells are ingested. Based on studies in which human cells were artificially stiffened, it was suggested that amoebae perform phagocytosis on stiffer cells, and trogocytosis on less stiff cells. A handful of recent studies of macrophages that used artificial targets or artificially stiffened target cells also suggested a similar relationship between target stiffness and trogocytosis/phagocytosis efficiencies. To better evaluate the impact of target cell stiffness on amoebic ingestion, instead of using artificial targets or artificial cell stiffening, we created human cell mutants in which individual Rho-pathway genes were knocked down. Strikingly, amoebae performed quantitatively reduced levels of trogocytosis on all knockdown mutants, regardless of cytoskeletal F-actin organization. In contrast, amoebic phagocytosis efficiency was inversely correlated with human cell cortical F-actin density. Thus, human cell F-actin organization differentially influences amoebic trogocytosis and phagocytosis. This is more complex than the conclusions of studies that used artificial targets or artificially stiffened cells. Our results emphasize that the dynamic nature of the cytoskeleton in living cells impacts trogocytosis. In addition to shedding light on the burgeoning field of eukaryotic trogocytosis, this work extends knowledge of amoebic ingestion processes that contribute to disease.

microbiology↗

bioRxiv2024

Cross-species protection suggests Entamoeba histolytica trogocytosis enables complement resistance through the transfer of negative regulators of complement activation

Entamoeba histolytica is a major cause of diarrheal disease. E. histolytica trophozoites ("amoebae") can invade the intestine and disseminate via the bloodstream, resisting complement lysis through unknown mechanisms. Amoebae kill human cells by performing trogocytosis. After performing trogocytosis, amoebae display human proteins on their own surface and are resistant to lysis by human serum. In this study we sought to further evaluate the mechanism by which amoebae resist complement. To test if complement is responsible for lysis of amoebae, C3-depleted serum was compared to replete serum, and C3 was required for lysis. Amoebae were allowed to perform trogocytosis of human cells and exposed to mouse serum. Although they had performed trogocytosis on a different species than the source of the serum, they were protected from lysis. To test if the protection from lysis by mouse serum was due to the functional interchangeability of human and mouse complement pathway proteins, human CD46 or CD55 (negative regulators of complement activation) were exogenously expressed. Amoebae that expressed human CD46 or CD55 were protected from lysis by mouse serum, indicating that display of human proteins was sufficient to inhibit mouse complement activation. Finally, amoebae were allowed to perform trogocytosis of a cell type in which the complement pathway is not conserved, and they did not become resistant to lysis. Overall, these findings are consistent with the model that trogocytosis enables amoebic acquisition and display of host proteins, including negative regulators of the complement pathway, that provide protection from complement lysis. Since other microbes can perform trogocytosis, this novel mechanism for complement resistance might apply to other infections.

microbiology↗

bioRxiv2021

Entamoeba histolytica develops resistance to complement deposition and lysis after acquisition of human complement regulatory proteins through trogocytosis

Entamoeba histolytica is the cause of amoebiasis. The trophozoite (amoeba) form of this parasite is capable of invading the intestine, and can disseminate through the bloodstream to other organs. The mechanisms that allow amoebae to evade complement deposition during dissemination have not been well characterized. We previously discovered a novel complement-evasion mechanism employed by E. histolytica. E. histolytica ingests small bites of living human cells in a process termed trogocytosis. We demonstrated that amoebae were protected from lysis by human serum following trogocytosis of human cells, and that amoebae acquired and displayed human membrane proteins from the cells they ingested. Here, we aimed to define how amoebae are protected from complement lysis after performing trogocytosis. We found that amoebae were protected from complement lysis after ingestion of both human Jurkat T cells and red blood cells, and that the level of protection correlated with the amount of material ingested. Trogocytosis of human cells led to a reduction in deposition of C3b on the surface of amoebae. We asked whether display of human complement regulators is involved in amoebic protection, and found that CD59 was displayed by amoebae after trogocytosis. Deletion of a single complement regulatory protein, CD59 or CD46, from Jurkat cells was not sufficient to alter amoebic protection from lysis, suggesting that multiple, redundant complement regulators mediate amoebic protection. However, exogeneous expression of CD46 or CD55 in amoebae was sufficient to confer protection from lysis. These studies shed light on a novel strategy for immune evasion by a pathogen. IMPORTANCEEntamoeba histolytica is the cause of amoebiasis, a diarrheal disease of global importance. While infection is often asymptomatic, the trophozoite (amoeba) form of this parasite is capable of invading and ulcerating the intestine, and can disseminate through the bloodstream to other organs. Understanding how E. histolytica evades the complement system during dissemination is of great interest. Here we demonstrate for the first time that amoebae that have performed trogocytosis (nibbling of human cells) resist deposition of the complement protein C3b. Amoebae that have performed trogocytosis display the complement regulatory protein CD59. Overall, our studies suggest that acquisition and display of multiple, redundant complement regulators is involved in amoebic protection from complement lysis. These findings shed light on a novel strategy for immune evasion by a pathogen. Since other parasites use trogocytosis for cell killing, our findings may apply to the pathogenesis of other infections.

microbiology↗

bioRxiv2020

Establishment of quantitative RNAi-based forward genetics in Entamoeba histolytica and identification of genes required for growth

While Entamoeba histolytica remains a globally important pathogen, it is dramatically understudied. The tractability of E. histolytica has historically been limited, which is largely due to challenging features of its genome. To enable forward genetics, we constructed and validated the first genome-wide E. histolytica RNAi knockdown mutant library. This library allows for Illumina deep sequencing analysis for quantitative identification of mutants that are enriched or depleted after selection. We developed a novel analysis pipeline to precisely define and quantify gene fragments. We used the library to perform the first RNAi screen in E. histolytica and identified slow growth (SG) mutants. Among genes targeted in SG mutants, many had annotated functions consistent with roles in cellular growth or metabolic pathways. Some targeted genes were annotated as hypothetical or lacked annotated domains, supporting the power of forward genetics in uncovering functional information that cannot be gleaned from databases. While the localization of neither of the proteins targeted in SG1 nor SG2 mutants could be predicted by sequence analysis, we showed experimentally that SG1 localized to the cytoplasm and cell surface, while SG2 localized to the cytoplasm. Overexpression of SG1 led to increased growth, while expression of a truncation mutant did not lead to increased growth, and thus aided in defining functional domains in this protein. Finally, in addition to establishing forward genetics, we uncovered new details of the unusual E. histolytica RNAi pathway. These studies dramatically improve the tractability of E. histolytica and open up the possibility of applying genetics to improve understanding of this important pathogen. Author SummaryEntamoeba histolytica is a globally important pathogen that is dramatically understudied. One of the major limitations of this organism is its challenging genome. RNAi is the state-of-the-art tool for genetic manipulation in E. histolytica, though the RNAi pathway has several noncanonical features. Here, we harnessed the RNAi pathway to enable RNAi-based forward genetics for the first time in this organism. We validated the RNAi library by performing the first E. histolytica RNAi screen and identified slow growth mutants. We showed that independently-generated mutants also exhibited slow growth phenotypes, and we characterized protein localization and domains for some of the identified slow growth genes. The RNAi library that we constructed enables modern, quantitative Illumina deep sequencing analysis to identify mutants that are enriched or depleted after selection. We developed a novel analysis pipeline to precisely define and quantify full-length gene fragments inferred from read mapping. Our approach differs from previous approaches for analysis of RNAi screens, and it better represents the actual DNA fragments and their quantities. This study dramatically improves the tractability of this important pathogen. Moreover, the strategies behind this RNAi library, and its analysis, are novel, and can be applied to other organisms. Author ContributionsA.B. designed and performed the experiments, except fragmentation of gDNA, immunofluorescence, and growth curves with expression of full-length or truncated proteins. R.L.S. performed SG1 and SG2 immunofluorescence experiments. M.C.R. performed growth curves with expression of full-length or truncated proteins. W.H. generated transfectants expressing full-length SG2. C.G.B. fragmented gDNA and processed the fragments to enable subsequent plasmid library construction. T.S.Y.T. and H.W.M. performed Gal/GalNAc lectin immunofluorescence experiments. S.S.H. designed the analysis strategy for Illumina sequencing data, and analyzed all Illumina sequencing data. M.L.S. oversaw the Illumina analysis approach. K.S.R. performed growth curves, conceived of the overall approach and oversaw the design and analysis of the experiments. A.B., S.S.H., and K.S.R. wrote the manuscript.

microbiology↗

bioRxiv2019

Direct and High-Throughput Assays for Human Cell Killing through Trogocytosis by Entamoeba histolytica

Entamoeba histolytica is a microbial eukaryote and causative agent of the diarrheal disease amoebiasis. Pathogenesis is associated with profound damage to human tissues, and treatment options are limited. We discovered that amoebae attack and kill human cells through a cell-nibbling process that we named trogocytosis (trogo-: nibble). Trogocytosis is likely to underlie tissue damage during infection and it represents a potential target for therapeutic intervention, although the mechanism is still unknown. Assays in current use to analyze trogocytosis by amoebae have not been amenable to studying different types of human cells, or to high-throughput analysis. Here, we developed two complementary assays to measure trogocytosis by quantifying human cell viability, both of which can be used for suspension and adherent cells. The first assay uses CellTiterGlo, a luminescent readout for cellular ATP levels, as a proxy for cell viability. We found that the CellTiterGlo signal is proportional to the quantity of viable cells, and can be used to detect death of human cells after co-incubation with amoebae. We established a second assay that is microscopy-based and uses two fluorescent stains to directly differentiate live and dead human cells. Both assays are simple and inexpensive, can be used with suspension and adherent human cell types, and are amenable to high-throughput approaches. These new assays are tools to improve understanding of amoebiasis pathogenesis.

microbiology↗

bioRxiv2018

Trogocytosis by Entamoeba histolytica mediates acquisition and display of human cell membrane proteins and evasion of lysis by human serum

Entamoeba histolytica is the protozoan parasite responsible for amoebiasis. We previously showed that E. histolytica kills human cells through a mechanism that we termed trogocytosis (trogo-: nibble), due to its resemblance to trogocytosis in other organisms. In parasites, trogocytosis is used to kill host cells. In multicellular organisms, trogocytosis is used for cell-cell interactions in the immune system, in the central nervous system, and during development. Thus, nibbling is an emerging theme in cell-cell interactions both within and between species, and it is relevant to host-pathogen interactions in many different contexts. When trogocytosis occurs between mammalian immune cells, cell membrane proteins from the nibbled cell can be acquired and displayed by the recipient cell. In this study, we tested the hypothesis that through trogocytosis of human cells, amoebae acquire and display human cell membrane proteins. Here we demonstrate for the first time that through trogocytosis, E. histolytica acquires and displays human cell membrane proteins and that this leads to protection from lysis by human serum. Protection from human serum only occurs after amoebae have undergone trogocytosis of live cells, but not phagocytosis of dead cells. Likewise, mutant amoebae that exhibit a phagocytosis defect, but are unaltered in their capacity to perform trogocytosis, are nevertheless protected from human serum. Our studies are the first to demonstrate that amoebae can display human cell membrane proteins and suggest that acquisition and display of membrane proteins is a general feature of trogocytosis that is not restricted to trogocytosis between mammalian immune cells. These studies have major implications for interactions between E. histolytica and the immune system and also reveal a novel strategy for immune evasion by a pathogen. Since other microbial eukaryotes use trogocytosis for cell killing, our findings may apply to the pathogenesis of other infections.\n\nAuthor SummaryEntamoeba histolytica is an intestinal parasite that causes amoebiasis, a potentially fatal diarrheal disease. Abscesses in organs outside of the intestine, such as the liver, can occur when amoebae are able to breach the intestinal wall and travel through the blood stream to other areas of the body. We previously showed that E. histolytica kills human cells by taking \"bites\" of human cell material in a process that we named trogocytosis (trogo-: nibble). Mammalian immune cells use trogocytosis to acquire proteins from other cells which impacts cell-cell communication. Here we tested the hypothesis that trogocytosis allows E. histolytica to acquire and display proteins from human cells allowing amoebae to survive in the blood stream. We demonstrate for the first time that through trogocytosis, E. histolytica acquires and displays human cell membrane proteins. We also demonstrate that trogocytosis of human cells allows amoebae to survive in human serum. These studies reveal a novel strategy for immune evasion by a pathogen and may apply to the pathogenesis of other infections.

microbiology↗