Vesicular transport across the fungal cell wall

Abstract

Recent findings indicate that fungi use vesicular transport to deliver substances across their cell walls. Fungal vesicles are similar to mammalian exosomes and could originate from cytoplasmic multivesicular bodies. Vesicular transport enables the export of large molecules across the cell wall, and vesicles contain lipids, proteins and polysaccharides, many of which are associated with virulence. Concentration of fungal products in vesicles could increase their efficiency in food acquisition and/or delivering potentially noxious substances to other cells, such as amoebae or phagocytes. The discovery of vesicular transport in fungi opens many new avenues for investigation in basic cell biology and pathogenesis.

Figure 1

Vesicles in the cell wall of Histoplasma capsulatum. Electron microscopic image of (A) H. capsulatum yeast cell with vesicles within the cell wall (arrows) and associated with the cell wall (arrowhead). (B) Heterogeneous extracellular vesicles from H. capsulatum isolated by ultracentrifugation from fungal culture supernatants. Inset shows enlarged section of vesicle highlighting double layer membranes. Note the heterogeneity in size and electron dense appearance. Scale bars: (a) 0.5 µm; (b) 0.5 µm.

Figure 2

Scheme for vesicle synthesis in fungal cells. (a) The fungal cell wall. The production of extracellular enzymes, pigments, glycoproteins and polysaccharides by fungal cells implies the existence of trans-cell wall mechanisms of molecular export. (b) Mechanisms of vesicle formation and passage could involve multivesicular body formation for exosome release (upper panels) or simple membrane budding (bottom panels). Extracellular vesicles are labeled with arrows. Vesicle contents could be released by membrane lysis for use in regular physiologic events or for delivery into host tissues.