Mucor rouxii ultrastructure: cyclic AMP and actin cytoskeleton

Abstract

A comparative analysis of the effect of two compounds, dibutyryl-cyclic-AMP (dbcAMP) and latrunculin B, on the morphology and ultrastructure of the dimorphic fungus Mucor rouxii under aerobic growth conditions is presented. dbcAMP acts through the sustained activation of protein kinase A, and latrunculin B through the disruption of the actin cytoskeleton. Upon addition of these compounds to the growth medium at any stage of the germination process, cells lost polarised growth and switched to isodiametric growth. The effect was reversible. The morphologies, visualised by light microscopy or scanning electron microscopy (SEM), were alike. A switch from a rough to a smooth surface was observed by SEM when cells were repolarised by removal of the added compound. Ultrastructural changes under both conditions, as observed by transmission electron microscopy, were similar, the main feature being the enlargement of the cell wall, with irregular depositions, and detachment from the cell membrane. dbcAMP-treated cells showed a decrease in the number of glycogen granules compared with control and latrunculin B-treated cells. F-actin staining with fluorescein isothiocyanate-phalloidin showed that both dbcAMP- and latrunculin B-treated cells displayed a much lower fluorescence than control cells, with only a few pale plaques. The results suggest that the sustained activation of protein kinase A, which impairs polarised growth, might exert its effect through a modification of actin cytoskeleton organisation, very probably also involving an integrinlike pathway, as judged by the cell wall detachment and loss of cell adhesiveness of the dbcAMP-treated isodiametric cells.

Calcineurin Plays Key Roles in the Dimorphic Transition and Virulence of the Human Pathogenic Zygomycete Mucor circinelloides

“…Several other studies have implicated protein kinase A in this response [25]–[31]. Other factors known to be involved predominantly alter mitochondrial functions.…”

“…(reviewed in [12] and references therein). cAMP activates cAMP-dependent protein kinase A (PKA), implicating a role for protein kinase A in the Mucor dimorphic transition, and this is supported by a series of recent studies, including genetic analyses in which genes encoding PKA regulatory subunits were disrupted by homologous recombination [25]–[31]. PKA also plays a key role in various morphogenesis processes including germination, branching, and polarized growth in Mucor [26], [32]–[37] …”

Acritarch Evidence for an Ediacaran Adaptive Radiation of Fungi

“…These long filaments of comparable materials to the sphe ri cal vesicle are similar to hyphae of Glomeromycotan spores, saccules and vesicles (Wu et al 1995, Walker et al, 2004, Sieverding & Oehl 2006, Pereyra et al 2006, Schüßler 2012. Similar basal tubular strucutres and wall extensions are also found in the 2200 Ma problematicum Diskagma (Re ta llack et al 2013 a).…”

“…Dinoflagellates, prasinophytes and chlorophytes are aqua tic eukaryotic phytoplankton (Moczydłowska et al 2011). Fungi are marine and terrestrial, eukaroytic de com po sers, and include acritarch-like structures in Glo me ro my co ta, orders Glomales (mycorrhizae: Wu et al 1995), and Archaeo sporales (Geosiphon : Schüßler 2012), and Muco ro myco tina (classification of Hibbett et al 2007), Order Mu co ra les (molds: Pereyra et al 2006). Mesomycetozoa are most ly fish parasites, but include spores with palintomic clus ters of cells deceptively similar to animal embryos (Huldt gren et al 2011).…”

Mucor rouxii Rho1 protein; characterization and possible role in polarized growth

“…This behaviour suggests the Rho1 protein might participate in the cell wall integrity pathway in M. rouxii. Recent results from our group (Pereyra et al 2006) indicate that sustained activation of PKA leads to a profound alteration of the cell wall. It will be interesting to investigate whether b-1,3-glucans have a regulatory role in fungal morphology and whether there is a cross talk with PKA signalling.…”