Dynamic development of parasitophorous vacuole of Eimeria tenella transfected with the yellow fluorescent protein gene fused to different signal sequences from apicomplexan parasites

Genetic manipulation for the non-model protozoan Eimeria: Advancements, challenges, and future perspective

Eimeria parasites pose a significant global threat to animal health, necessitating improved and cost-effective control measures. Genetic manipulation is pivotal for understanding Eimeria biology and designing targeted control strategies. Recent advancements, including genome sequencing and the development of transient and stable transfection systems, have significantly enhanced insights into the molecular biology of Eimeria. These advancements have paved the way for cutting-edge techniques like CRISPR-Cas9 gene editing. This review summarizes the key milestones in the development of genetic manipulation platforms for Eimeria and their transformative applications, such as the development of next-generation drugs, vaccines, and Eimeria-based vaccine vectors. Furthermore, this review provides insights that could be applicable to the establishment of genetic tools for other protozoan organisms.

Live attenuated anticoccidial vaccines for chickens

Chicken coccidiosis, caused by infection with single or multiple Eimeria species, results in significant economic losses to the global poultry industry. Over the past decades, considerable efforts have been made to generate attenuated Eimeria strains, and the use of live attenuated anticoccidial vaccines for disease prevention has achieved tremendous success. In this review, we evaluate the advantages and limitations of the methods of attenuation as well as attenuated Eimeria strains in a historical perspective. Also, we summarize the recent exciting research advances in transient/stable transfection systems and clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing developed for Eimeria parasites, and discuss trends and challenges of developing live attenuated anticoccidial vaccines based on transgenesis and genome editing.

Towards Innovative Design and Application of Recombinant Eimeria as a Vaccine Vector

Efficient delivery of antigenic cargo to trigger protective immune responses is critical to the success of vaccination. Genetically engineered microorganisms, including virus, bacteria, and protozoa, can be modified to carry and deliver heterologous antigens to the host immune system. The biological vectors can induce a broad range of immune responses and enhance heterologous antigen-specific immunological outcomes. The protozoan genus Eimeria is widespread in domestic animals, causing serious coccidiosis. Eimeria parasites with strong immunogenicity are potent coccidiosis vaccine candidates and offer a valuable model of live vaccines against infectious diseases in animals. Eimeria parasites can also function as a vaccine vector. Herein, we review recent advances in design and application of recombinant Eimeria as a vaccine vector, which has been a topic of ongoing research in our laboratory. By recapitulating the establishment of an Eimeria transfection platform and its application, it will help lay the foundation for the future development of effective parasite-based vaccine delivery vectors and beyond.

Identification and Application of Epitopes in EtMIC1 of Eimeria tenella Recognized by the Monoclonal Antibodies 1-A1 and 1-H2

Eimeria tenella microneme-1 protein (EtMIC1) has been proposed to be a transmembrane protein, but this characteristic has not yet been confirmed experimentally. Furthermore, despite EtMIC1 being an important candidate antigen, its key epitope has not been reported. Here, two linear B-cell epitopes of EtMIC1, 91LITFATRSK99 and 698ESLISAGE705, were identified by Western blotting using specific monoclonal antibodies (MAbs) and were named epitope I (located in the I-domain) and epitope CTR (located in the CTR domain), respectively. Sequence comparative analyses of these epitopes among Eimeria species that infect chickens showed that epitope I differs greatly across species, whereas epitope CTR is relatively conserved. Point mutation assay results indicate that all the amino acid residues of the epitopes recognized by MAb 1-A1 or 1-H2 are key amino acids involved in recognition. Comparative analyses of indirect immunofluorescence assay (IFA) results for MAbs 1-A1 and 1-H2 under both nonpermeabilization and permeabilization conditions indicate that epitope I is located on the outer side of the sporozoite surface membrane whereas epitope CTR is located on the inner side, together providing experimental evidence that EtMIC1 is a transmembrane protein. IFA also labeled the EtMIC1 protein on the parasitophorous vacuole membrane and on the surface of schizonts, which suggests that the EtMIC1 protein may play an important role in parasitophorous vacuole formation and E. tenella development. Immunoprotective efficacy experiments revealed that epitope I has good immunogenicity, as evidenced by its induction of high serum antibody levels, blood lymphocyte proliferation, and CD4+ blood lymphocyte percentage.

Laboratory Growth and Genetic Manipulation of Eimeria tenella

Eimeria is a genus of apicomplexan parasites that contains a large number of species, most of which are absolutely host-specific. Seven species have been recognized to infect chickens. Infection of susceptible chickens results in an intestinal disease called coccidiosis, characterized by mucoid or hemorrhagic enteritis, which is associated with impaired feed conversion or mortality in severe cases. Intensive farming practices have increased the significance of coccidiosis since parasite transmission is favored by high-density housing of large numbers of susceptible chickens. Routine chemoprophylaxis and/or vaccination with live parasite vaccines provides effective control of Eimeria, although the emergence of drug resistance and the relative cost and production capacity of current vaccine lines can prove limiting. As pressure to reduce drug use in livestock production intensifies, novel vaccination strategies are needed. Development of effective protocols supporting genetic complementation of Eimeria species has until recently been hampered by their inability to replicate efficiently in vitro. Now, the availability of such protocols has raised the prospect of generating transgenic parasite lines that function as vaccine vectors to express and deliver heterologous antigens. For example, this technology has the potential to streamline the production of live anticoccidial vaccines through the generation of parasite lines that co-express immunoprotective antigens derived from multiple Eimeria species. In this paper we describe detailed protocols for genetic manipulation, laboratory growth, and in vivo propagation of Eimeria tenella parasites, which will encourage future work from other researchers to expand biological understanding of Eimeria through reverse genetics. © 2019 by John Wiley & Sons, Inc.

Transgenic Eimeria mitis expressing chicken interleukin 2 stimulated higher cellular immune response in chickens compared with the wild-type parasites

Chicken coccidiosis, caused by Eimeria sp., occurs in almost all poultry farms and causes huge economic losses in the poultry industry. Although this disease could be controlled by vaccination, the reduced feed conservation ratio limits the widespread application of anticoccidial vaccines in broilers because some intermediate and/or low immunogenic Eimeria sp. only elicit partial protection. It is of importance to enhance the immunogenicity of these Eimeria sp. by adjuvants for more effective prevention of coccidiosis. Cytokines have remarkable effects on the immunogenicity of antigens. Interleukin 2 (IL-2), for example, significantly stimulates the activation of CD8+ T cells and other immune cells. In this study, we constructed a transgenic Eimeria mitis line (EmiChIL-2) expressing chicken IL-2 (ChIL-2) to investigate the adjuvant effect of ChIL-2 to enhance the immunogenicity of E. mitis against its infection. Stable transfected EmiChIL-2 population was obtained by pyrimethamine selection and verified by PCR, genome walking, western blotting and indirect immunofluorescence assay. Cellular immune response, E. mitis-specific IFN-γ secretion lymphocytes in the peripheral blood mononuclear cells, stimulated by EmiChIL-2 was analyzed by enzyme-linked immunospot assay (ELISPOT). The results showed that EmiChIL-2 stimulated a higher cellular immune response compared with that of the wild-type parasite infection in chickens. Moreover, after the immunization with EmiChIL-2, elevated cellular immune response as well as reduced oocyst output were observed These results indicated that ChIL-2 expressed by Eimeria sp. functions as adjuvant and IL-2 expressing Eimeria parasites are valuable vaccine strains against coccidiosis.

A selective review of advances in coccidiosis research

Coccidiosis is a widespread and economically significant disease of livestock caused by protozoan parasites of the genus Eimeria. This disease is worldwide in occurrence and costs the animal agricultural industry many millions of dollars to control. In recent years, the modern tools of molecular biology, biochemistry, cell biology and immunology have been used to expand greatly our knowledge of these parasites and the disease they cause. Such studies are essential if we are to develop new means for the control of coccidiosis. In this chapter, selective aspects of the biology of these organisms, with emphasis on recent research in poultry, are reviewed. Topics considered include taxonomy, systematics, genetics, genomics, transcriptomics, proteomics, transfection, oocyst biogenesis, host cell invasion, immunobiology, diagnostics and control.

A novel serine/threonine protein phosphatase type 5 from second-generation merozoite of Eimeria tenella is associated with diclazuril-induced apoptosis

Screening the anticoccidial drug targets is very important for developing novel drugs and revealing the molecular basis of drug resistance in coccidia. Due to high effectivity and safety, diclazuril was used widely in the poultry industry. To assess the roles of the serine/threonine protein phosphatase type 5 of second-generation merozoites in Eimeria tenella (EtPP5) in the anticoccidial activity of diclazuril against chicken coccidiosis, EtPP5 was cloned using reverse transcriptase polymerase chain reaction and rapid amplification of cDNA ends. Ultrastructural changes in second-generation merozoites and mRNA expression level of EtPP5 were monitored by transmission electron microscopy (TEM) and quantitative real-time PCR, respectively. The results showed that the full length of the cloned EtPP5 cDNA (2,495 bp) encompassed a 1,647-bp open reading frame encoding a polypeptide of 548 residues with an estimated molecular mass of 60.82 kDa and a theoretical isoelectric point of 5.89. Molecular analysis of EtPP5 reveals the presence of a C-terminal phosphatase domain and an extended N-terminal tetratricopeptide repeat motif, a typical feature of protein phosphatases. The cDNA sequence has been submitted to the GenBank database with accession number JX987508. EtPP5 shared 89% homology with the published sequence of a PP5 ortholog of Toxoplasma gondii at the amino acid level (GenBank XP_002364442.1). TEM observed that diclazuril induced ultrastructural changes in second-generation merozoites. Quantitative real-time PCR analysis showed that compared with the control group, the level of EtPP5 mRNA expression was significantly downregulated by 51.4% by diclazuril treatment. The high similarity of EtPP5 to previously described PP5 of other organisms, as well as its downregulated expression and connection with apoptosis in the second-generation merozoites induced by diclazuril, suggests that it could act an important role in understanding the signaling mechanism underlining the diclazuril-induced merozoites apoptosis.

piggyBac transposon-mediated transgenesis in the apicomplexan parasite Eimeria tenella

piggyBac, a type II transposon that is useful for efficient transgenesis and insertional mutagenesis, has been used for effective and stable transfection in a wide variety of organisms. In this study we investigate the potential use of the piggyBac transposon system for forward genetics studies in the apicomplexan parasite Eimeria tenella. Using the restriction enzyme-mediated integration (REMI) method, E. tenella sporozoites were electroporated with a donor plasmid containing the enhanced yellow fluorescent protein (EYFP) gene flanked by piggyBac inverted terminal repeats (ITRs), an Asc I-linearized helper plasmid containing the transposase gene and the restriction enzyme Asc I. Subsequently, electroporated sporozoites were inoculated into chickens via the cloacal route and transfected progeny oocysts expressing EYFP were sorted by flow cytometry. A transgenic E. tenella population was selected by successive in vivo passage. Southern-blotting analysis showed that exogenous DNA containing the EYFP gene was integrated into the parasite genome at a limited number of integration sites and that the inserted part of the donor plasmid was the fragment located between the 5′ and 3′ ITRs as indicated by primer-specific PCR screening. Genome walking revealed that the insertion sites were TTAA-specific, which is consistent with the transposition characteristics of piggyBac.

Co-expression of reporter genes in the widespread pathogen Eimeria tenella using a double-cassette expression vector strategy

The double-cassette expression vector strategy is valuable for many studies, including comparative analysis of the function of promoters and expression of genes in different compartments. In this study, we report co-expression of enhanced yellow fluorescent protein (EYFP) and red fluorescent protein (RFP) in Eimeria tenella transfected with two double-cassette expression vectors, pMIC-EYFP/ACT-RFP and pMIC-EYFP/ACTss-RFP. The results showed that under regulation of the mic1 promoter, EYFP was expressed in sporulated oocysts but not in unsporulated ones, while under regulation of the actin promoter RFP was expressed in both forms. We found that the signal peptide of Toxoplasma gondii dense granule protein 8 (GRA8) located the RFP expression to the parasitophorous vacuoles of the parasites, the margins of the unsporulated oocysts and the cavities of the sporocysts. The feasibility of co-expression of exogenous proteins in E. tenella is important for the development of transgenic E. tenella as a novel vaccine vector.

Synthetic peptides from conserved regions of the Plasmodium falciparum early transcribed membrane and ring exported proteins bind specifically to red blood cell proteins

Severe malaria pathology is directly associated with cytoadherence of infected red blood cells (iRBCs) to healthy RBCs and/or endothelial cells occurring during the intraerythrocytic development of Plasmodium falciparum. We synthesized, as 20-mer long peptides, the members of the ring exported (REX) protein family encoded in chromosome 9, as well as the early transcribed membrane proteins (E-TRAMP) 10.2 and 4, to identify specific RBC binding regions in these proteins. Twelve binding peptides were identified (designated as HABPs): three were identified in REX1, two in REX2, one in REX3, two in REX4 and four in E-TRAMP 10.2. The majority of these HABPs was conserved among different P. falciparum strains, according to sequence analysis. No HABPs were found in E-TRAMP 4. Bindings of HABPs were saturable and sensitive to the enzymatic treatment of RBCs and HABPs had different structural features, according to circular dichroism studies. Our results suggest that the REX and E-TRAMP families participate in relevant interactions with RBC membrane proteins, which highlight these proteins as potential targets for the development of fully effective immunoprophylactic methods.