The Fungal Type II Myosin in Penicillium marneffei, MyoB, Is Essential for Chitin Deposition at Nascent Septation Sites but Not Actin Localization

Abstract

Cytokinesis is essential for proliferative growth but also plays equally important roles during morphogenesis and development. The human pathogen Penicillium marneffei is capable of dimorphic switching in response to temperature, growing in a multicellular filamentous hyphal form at 25°C and in a unicellular yeast form at 37°C. P. marneffei also undergoes asexual development at 25°C to produce multicellular differentiated conidiophores. Thus, P. marneffei exhibits cell division with and without cytokinesis and division by budding and fission, depending on the cell type. The type II myosin gene, myoB, from P. marneffei plays important roles in the morphogenesis of these cell types. Deletion of myoB leads to chitin deposition defects at sites of cell division without perturbing actin localization. In addition to aberrant hyphal cells, distinct conidiophore cell types are lacking due to malformed septa and nuclear division defects. At 37°C, deletion of myoB prevents uninucleate yeast cell formation, instead producing long filaments resembling hyphae at 25°C. The ⌬myoB cells also often lyse due to defects in cell wall biogenesis. Thus, MyoB is essential for correct morphogenesis of all cell types regardless of division mode (budding or fission) and defines differences between the different types of growth.

Morphogenetic Circuitry Regulating Growth and Development in the Dimorphic Pathogen Penicillium marneffei

“…Deletion of the type II myosin gene myoB results in conidiophores that lack clearly defined cell types. Typically, stalks produced a "phialide-like" cell from which a single terminal conidium was observed and conidiophores lacked or possessed malformed septa separating the metula-phialide and conidiumphialide boundaries (45). This suggests that the sequential production of metulae, phialides, and conidia by budding is contingent on the successful completion of septation.…”

“…This suggests that the sequential production of metulae, phialides, and conidia by budding is contingent on the successful completion of septation. ⌬myoB conidiophores also contained nuclei with aberrant morphology, suggesting that the conidiophore septa may be playing a spatial role in the placement of nuclei in the conidiophore (45). Deletion of the PAK encoded by pakB results in conidiophores with normal metulae and phialides but only a single abnormally large terminal conidium (32).…”

“…Therefore, mutations in genes involved in this process leads to a loss of yeast cell production. Deletion of the type II myosin gene essential for cytokinesis, myoB, leads to a loss of arthroconidiation, and the deletion mutant therefore continues to grow as aseptate, branched, and aberrant hyphae at 37°C (45). Haploinsufficiency or depletion of rfxA, which encodes the RFX transcription factor that regulates nuclear division, blocks yeast cell morphogenesis, and only swollen, irregularly shaped arthroconidial hyphae with nuclear or cell lysis defects are produced.…”

Distinct Roles of Myosins in Aspergillus fumigatus Hyphal Growth and Pathogenesis

“…The conventional myosins, class II myosins, have a role in cytokinesis through involvement in the cytokinetic actomyosin ring (CAR) (21). Deletion of the class II myosins in Talaromyces (formerly Penicillium) marneffei and A. nidulans led to cytokinesis defects or septation failure (5,22). In addition, mutants lacking the sole class II myosin in A. nidulans (MyoB) exhibited a lack of conidiation, extreme growth defects, and improper chitin deposition (5).…”

Thermally Dimorphic Human Fungal Pathogens—Polyphyletic Pathogens with a Convergent Pathogenicity Trait

“…These tools have been used to probe the molecular mechanisms that control the dimorphic switch and allow the fungus to survive within the host. These include (1) a very high frequency DNA-mediated transformation procedure using PEG-based protoplast fusions that results in integration of exogenous DNA (Borneman et al 2001), (2) dominant selectable markers with matching recipient strains for transformation , (3) enhanced strains in which DNA integration is strictly by homologous recombination using mutants in the nonhomologous endjoining (NHEJ) system , (4) strains expressing fluorescent proteins for livecell tracking , (5) antisense RNA knockdown systems (Canovas et al 2011), (6) gateway systems for rapid construct generation Bugeja et al 2012), (7) promoters for controlled expression of genes (Borneman et al 2000;Boyce et al 2001), (8) genomic and transcriptomic technologies (Pasricha et al 2013), and (9) cell culture, zebrafish, and mouse-based systems for virulence testing (Boyce and Andrianopoulos 2007;Ellett et al 2011;Henk et al 2012). A procedure for DNAmediated transformation using the Agrobacterium transfer-DNA system has also been described (Kummasook et al 2010).…”