Factors Regulating Morphogenesis in Coccidioides Immitis

Cole, Garry T.; Kruse, D; Seshan, K. R.; Pan, Shanlin; Szaniszlo, Paul J.; Richardson, J. F.; Bian, Buming

doi:10.1007/978-1-4615-2834-0_16

Cited by 11 publications

(12 citation statements)

References 27 publications

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“…Arthroconidia first undergo isotropic growth to form spherule initials. On the basis of ultrastructural studies of this early stage of parasitic cell differentiation, it appears that a multitude of tiny vesicles first visible in spherule initials later coalesce to form a large central vacuole (9). Segmentation of the spherule cytoplasm occurs by ingrowth of the parasitic cell wall and results in the formation of compartments which surround the still-intact, central vacuole (9).…”

Section: Resultsmentioning

confidence: 99%

“…On the basis of ultrastructural studies of this early stage of parasitic cell differentiation, it appears that a multitude of tiny vesicles first visible in spherule initials later coalesce to form a large central vacuole (9). Segmentation of the spherule cytoplasm occurs by ingrowth of the parasitic cell wall and results in the formation of compartments which surround the still-intact, central vacuole (9). It is evident from examinations of thin sections of this stage of development that all of the cytoplasm of the presegmented spherule is not incorporated into the compartments that later differentiate into endospores.…”

Section: Resultsmentioning

confidence: 99%

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Urease Produced by Coccidioides posadasii Contributes to the Virulence of This Respiratory Pathogen

et al. 2006

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Urease activity during in vitro growth in the saprobic and parasitic phases of Coccidioides spp. is partly responsible for production of intracellular ammonia released into the culture media and contributes to alkalinity of the external microenvironment. Although the amino acid sequence of the urease of Coccidioides posadasii lacks a predicted signal peptide, the protein is transported from the cytosol into vesicles and the central vacuole of parasitic cells (spherules). Enzymatically active urease is released from the contents of mature spherules during the parasitic cycle endosporulation stage. The endospores, together with the urease and additional material which escape from the ruptured parasitic cells, elicit an intense host inflammatory response. Ammonia production by the spherules of C. posadasii is markedly increased by the availability of exogenous urea found in relatively high concentrations at sites of coccidioidal infection in the lungs of mice. Direct measurement of the pH at these infection sites revealed an alkaline microenvironment. Disruption of the urease gene of C. posadasii resulted in a marked reduction in the amount of ammonia secreted in vitro by the fungal cells. BALB/c mice challenged intranasally with the mutant strain showed increased survival, a wellorganized granulomatous response to infection, and better clearance of the pathogen than animals challenged with either the parental or the reconstituted (revertant) strain. We conclude that ammonia and enzymatically active urease released from spherules during the parasitic cycle of C. posadasii contribute to host tissue damage, which exacerbates the severity of coccidioidal infection and enhances the virulence of this human respiratory pathogen.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Urease Produced by Coccidioides posadasii Contributes to the Virulence of This Respiratory Pathogen

et al. 2006

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“…The experimental design used to generate the sterile mutant was based on our understanding of the morphogenetic events of the parasitic cycle of C. posadasii. Results of light-and electron-microscopic studies of the parasitic cycle in vitro and in vivo suggested that digestion of the chitin-rich septal wall complex of spherules is a pivotal event which coincides with the initiation of endospore formation (3,4). It was reasonable to assume that chitinase activity played a key role in this morphogenetic process, but our discovery of eight members of family 18 chitinases (21) in the C. posadasii genome presented a challenge to validate this hypothesis.…”

Section: Discussionmentioning

confidence: 99%

A Genetically Engineered Live Attenuated Vaccine ofCoccidioides posadasiiProtects BALB/c Mice against Coccidioidomycosis

et al. 2009

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Coccidioidomycosis (also known as San Joaquin Valley fever) is an occupational disease. Workers exposed to outdoor dust which contains spores of the soil-inhabiting fungus have a significantly increased risk of respiratory infection. In addition, people with compromised T-cell immunity, the elderly, and certain racial groups, particularly African-Americans and Filipinos, who live in regions of endemicity in the southwestern United States have an elevated incidence of symptomatic infection caused by inhalation of spores of Coccidioides posadasii or Coccidioides immitis. Recurring epidemics and escalation of medical costs have helped to motivate production of a vaccine against valley fever. The major focus has been the development of a defined, T-cell-reactive, recombinant protein vaccine. However, none of the products described to date have provided full protection to coccidioidal disease-susceptible BALB/c mice. Here we describe the first genetically engineered, live, attenuated vaccine that protects both BALB/c and C57BL/6 mice against coccidioidomycosis. Two chitinase genes (CTS2 and CTS3) were disrupted to yield the attenuated strain, which was unable to endosporulate and was no longer infectious. Vaccinated survivors mounted an immune response characterized by production of both T-helper-1-and T-helper-2-type cytokines. Histology revealed well-formed granulomas and markedly diminished inflammation. Significantly fewer organisms were observed in the lungs of survivors than in those of nonvaccinated mice. Additional investigations are required to further define the nature of the live, attenuated vaccine-induced immunity against Coccidioides infection.

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“…Chitin is a major component of the segmentation apparatus (5,10). A secreted 48-kDa chitinase, which has been shown to be an immunodominant, serodiagnostic complement fixation antigen (CF-Ag) of C. immitis (14), was suggested to play a pivotal role in the digestion of the segmentation wall during endospore formation (3,15). The CF-Ag-chitinase has been cloned (CTS1 [29]), and the recombinant protein expressed in E. coli has been crystallized.…”

Section: Discussionmentioning

confidence: 99%

“…Biochemical characterization of the purified 48-kDa polypeptide revealed that the antigen functions as a chitinase (15) and is secreted by C. immitis in both the saprobic and parasitic phases. It was suggested that the active chitinase associates with the segmentation wall of parasitic cells during early endosporulation (3) and participates in an essential process of cell wall modification as endospores undergo differentiation and subsequent release from the maternal spherule (4). The gene which encodes the CF antigen (CTS1) has been cloned (29), and temporal expression of the chitinase gene was evaluated in vitro during parasitic cell development (P. W. Thomas and G. T. Cole, Abstr.…”

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Disruption of the Gene Which Encodes a Serodiagnostic Antigen and Chitinase of the Human Fungal Pathogen Coccidioides immitis

et al. 2000

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Disruption of genes in medically important fungi has proved to be a powerful tool for evaluation of putative virulence factors and identification of potential protein targets for novel antifungal drugs. Chitinase has been suggested to play a pivotal role in autolysis of the parasitic cell wall of Coccidioides immitis during the asexual reproductive cycle (endosporulation) of this systemic pathogen. Two chitinase genes (CTS1 and CTS2) of C. immitis have been cloned. Preliminary evidence has suggested that expression of CTS1 is markedly increased during endospore formation. The secreted CTS1 chitinase has also been shown to react with patient antiCoccidioides complement-fixing (CF) antibody and is a valuable aid in the serodiagnosis of coccidioidomycosis. To examine the role of CTS1 in the morphogenesis of parasitic cells, the CTS1 gene was disrupted by a single, locus-specific crossover event. This resulted in homologous integration of a pAN7.1 plasmid construct that contained a 1.1-kb fragment of the chitinase gene into the chromosomal DNA of C. immitis. Results of Southern hybridizations, immunoblot analyses of culture filtrates using both CTS1-specific murine antiserum and serum from a patient with confirmed coccidioidal infection, an immunodiffusion test for CF antigenicity, and substrate gel electrophoresis assays of chitinase activity confirmed that the CTS1 gene was disrupted and nonfunctional. This is the first report of a successful targeted gene disruption in C. immitis. However, loss of CTS1 function had no effect on virulence or endosporulation. Comparative assays of chitinase activity in the parental and ⌬cts1 strains suggested that the absence of a functional CTS1 gene can be compensated for by elevated expression of the CTS2 gene. Current investigations are focused on disruption of CTS2 in the ⌬cts1 host to further evaluate the significance of chitinase activity in the parasitic cycle of C. immitis.

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Factors Regulating Morphogenesis in Coccidioides Immitis

Cited by 11 publications

References 27 publications

Urease Produced by Coccidioides posadasii Contributes to the Virulence of This Respiratory Pathogen

Urease Produced by Coccidioides posadasii Contributes to the Virulence of This Respiratory Pathogen

A Genetically Engineered Live Attenuated Vaccine ofCoccidioides posadasiiProtects BALB/c Mice against Coccidioidomycosis

Disruption of the Gene Which Encodes a Serodiagnostic Antigen and Chitinase of the Human Fungal Pathogen Coccidioides immitis

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