Dimorphism of <i>Penicillium marneffei</i> as observed by electron microscopy

Garrison, Robert G.; Boyd, Karen S.

doi:10.1139/m73-209

Cited by 48 publications

(24 citation statements)

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“…Consequently, 1% peptone solution seems to be the medium-of-choice for induction and maintenance of P. marneffei in the yeast form. To date, establishment of a hyphal network by P. marneffei conidia has not been detected in macrophages 1,2 . As a result, Andrianopoulos suggested that a direct conidium-to-yeast cell morphogenesis program might be activated by certain factors within macrophages 3 .…”

Section: Discussionmentioning

confidence: 99%

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Tongchusak¹,

Pongsunk²,

Watkins³

et al. 2006

ScienceAsia

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Penicillium marneffei is a dimorphic pathogenic fungus responsible for opportunistic infection in HIV infected individuals. The fungus displays dimorphic switching in response to temperature changes. At 25°C, it grows in mold form that produces penicilli conidia which are thought to be infectious. At 37°C, the fungus transforms into a fission yeast. To investigate this morphological conversion, P. marneffei conidia were grown in media supplemented with various organic substances. Sabouraud dextrose broth (SDB) supplemented with 4% yeast extract enhanced regular fission yeast production, whereas SDB alone and SDB supplemented with fetal bovine serum did not produce homogeneous cultures. The fungus in Sabouraud maltose broth exhibited filamentous hyphae, while its growth in Sabouraud galactose broth was inhibited. Yeast nitrogen base (YNB) medium supplemented with glucose gave hyphal growth and supplemented with N-acetylglucosamine (GlcNAc) gave retarded growth with multiseptate hyphae. Conidia-yeast conversion was not observed in YNB supplemented with glucose plus various amino acids. However, when 1% peptone was added to these YNB media, however, yeast cells or short multi-septate hyphae were produced. Surprisingly, conidia cultivated in distilled water containing 1% peptone gave uniform fission yeast similar to yeast cells found in clinical specimens. Thus, 1% peptone supplementation was responsible for the yeast transition and will serve as simple method to obtain pure P. marneffei yeasts for future studies on virulence, invasiveness, and pathogenesis.

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Section: Discussionmentioning

confidence: 99%

“…Penicillium marneffei is a newly emerging opportunistic dimorphic fungal pathogen causing a systemic disease in immunocompromised individuals, especially HIV infected patients 1,2 . Cell type switching in dimorphic fungi is thought to be modulated by environmental factors via cytoplasmic signal transduction.…”

Section: Introductionmentioning

confidence: 99%

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Tongchusak¹,

Pongsunk²,

Watkins³

et al. 2006

ScienceAsia

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“…The subsequent fragmentation of these filaments leads to the production of uninucleate yeast cells that divide by fission. It is this growth form of P. marneffei that presents as an intracellular pathogen in phagocytic cells during infection (10,25).Transition between multicellular and unicellular morphological states is common to most fungi and serve as an important process within developmental programs such as conidiation and mating. The process of arthroconidiation in P. marneffei is analogous to the transition from a hyphal growth form to a unicellular spore form in Acremonium chrysogenum and Coccidioides immitis, suggesting there may be common mechanisms underlying these events.…”

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The RFX Protein RfxA Is an Essential Regulator of Growth and Morphogenesis in Penicillium marneffei

2010

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Fungi are small eukaryotes capable of undergoing multiple complex developmental programs. The opportunistic human pathogen Penicillium marneffei is a dimorphic fungus, displaying vegetative (proliferative) multicellular hyphal growth at 25°C and unicellular yeast growth at 37°C. P. marneffei also undergoes asexual development into differentiated multicellular conidiophores bearing uninucleate spores. These morphogenetic processes require regulated changes in cell polarity establishment, cell cycle dynamics, and nuclear migration. The RFX (regulatory factor X) proteins are a family of transcriptional regulators in eukaryotes. We sought to determine how the sole P. marneffei RFX protein, RfxA, contributes to the regulation of morphogenesis. Attempts to generate a haploid rfxA deletion strain were unsuccessful, but we did isolate an rfxA ؉ /rfxA⌬ heterozygous diploid strain. The role of RfxA was assessed using conditional overexpression, RNA interference (RNAi), and the production of dominant interfering alleles. Reduced RfxA function resulted in defective mitoses during growth at 25°C and 37°C. This was also observed for the heterozygous diploid strain during growth at 37°C. In contrast, overexpression of rfxA caused growth arrest during conidial germination. The data show that rfxA must be precisely regulated for appropriate nuclear division and to maintain genome integrity. Perturbations in rfxA expression also caused defects in cellular proliferation and differentiation. The data suggest a role for RfxA in linking cellular division with morphogenesis, particularly during conidiation and yeast growth, where the uninucleate state of these cell types necessitates coupling of nuclear and cellular division tighter than that observed during multinucleate hyphal growth.We are interested in examining the regulatory networks controlling cell-type specification and development in the opportunistic fungal pathogen Penicillium marneffei and the role these processes play in pathogenicity. P. marneffei is a thermally dimorphic fungus capable of causing disseminated infection in immunocompromised individuals. Dimorphism is a common morphological process for many fungal pathogens and has been clearly linked to pathogenicity. At room temperature (25°C), P. marneffei exhibits mycelial growth in which multinucleate cells are connected in long hyphal filaments. This growth form is also capable of asexual development (conidiation), in which single-celled uninucleate spores (conidia) are produced on specialized aerial hyphae (conidiophores). The transition from a multicellular hyphal growth form to a unicellular growth form occurs upon transfer to 37°C. During this process, known as arthroconidiation, cellular and nuclear division become coupled and double septa are deposited between cells. The subsequent fragmentation of these filaments leads to the production of uninucleate yeast cells that divide by fission. It is this growth form of P. marneffei that presents as an intracellular pathogen in phagocytic cells during infection (10,...

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“…The ascomycete Penicillium marneffei is an opportunistic human pathogen endemic in Asia that exhibits a temperaturedependent dimorphic switch (12,17,23). At 25°C, multinucleate, septate hyphae are produced by apical growth and lateral branching.…”

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G-Protein Signaling Mediates Asexual Development at 25°C but Has No Effect on Yeast-Like Growth at 37°C in the Dimorphic Fungus Penicillium marneffei

2002

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The ascomycete Penicillium marneffei is an opportunistic human pathogen exhibiting a temperature-dependent dimorphic switch. At 25°C, P. marneffei grows as filamentous multinucleate hyphae and undergoes asexual development, producing uninucleate spores. At 37°C, it forms uninucleate yeast cells which divide by fission. We have cloned a gene encoding a G␣ subunit of a heterotrimeric G protein from P. marneffei named gasA with high similarity to fadA in Aspergillus nidulans. Through the characterization of a ⌬gasA strain and mutants carrying a dominant activating or a dominant interfering gasA allele, we show that GasA is a key regulator of asexual development but seems to play no role in the regulation of growth. A dominant activating gasA mutant whose mutation results in a G42-to-R change (gasA G42R ) does not express brlA, the conidiation-specific regulatory gene, and is locked in vegetative growth, while a dominant interfering gasA G203R mutant shows inappropriate brlA expression and conidiation. Interestingly, the gasA mutants have no apparent defect in dimorphic switching or yeast-like growth at 37°C. Growth tests on dibutyryl cyclic AMP (dbcAMP) and theophylline suggest that a cAMP-protein kinase A cascade may be involved in the GasA signaling pathway.Environmental signals leading to a variety of developmental processes and physiological responses are sensed and transduced to the cell interior through complex interactions at the cell membrane. Heterotrimeric guanine nucleotide-binding proteins (G proteins) act as signal transducers that couple cell surface receptors to cytoplasmic effector proteins in eukaryotes. Upon binding of the agonist with the corresponding serpentine transmembrane receptor, the G␣ subunit becomes activated, exchanging GDP for GTP and dissociating from the ␤␥ complex. G␣ and G␤␥ subunits can then interact with appropriate targets such as phosphodiesterases, protein kinases, adenylyl cyclases, phospholipases, and ion channels to trigger downstream signaling pathways (20,27,37,44).In fungi, G proteins affect a number of developmental and morphogenic processes and play essential roles during pathogenic and sexual development programs (4). The best-characterized fungal G␣ proteins are Saccharomyces cerevisiae Gpa1 and Gpa2. Gpa1 is linked to cell-type-specific pheromone receptors encoded by the STE2 and STE3 genes and plays a negative role in the mitogen-activated protein kinase pheromone signaling pathway that leads to mating (32). Gpa2 is required for the induction of pseudohyphal growth in diploid yeast cells under nitrogen starvation and signals through a cyclic AMP (cAMP)-dependent protein kinase A (PKA) pathway (30, 35). Interestingly, Gpa2 is coupled to a G-proteincoupled receptor, Gpr1, which appears to be a glucose sensor (28,33,36). G␣ subunits from other fungi with high homology to Gpa2 have also been implicated in morphogenesis through cAMP-PKA signaling. The corn smut fungus Ustilago maydis displays a dimorphic switch between a haploid yeast-like form and a pathogenic filamen...

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Dimorphism of Penicillium marneffei as observed by electron microscopy

Cited by 48 publications

References 0 publications

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The RFX Protein RfxA Is an Essential Regulator of Growth and Morphogenesis in Penicillium marneffei

G-Protein Signaling Mediates Asexual Development at 25°C but Has No Effect on Yeast-Like Growth at 37°C in the Dimorphic Fungus Penicillium marneffei

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