Does macrovesicular endocytosis occur in fungal hyphae?

Abstract

Like most eukaryotic organisms, fungi use endocytosis for nutrition, signal transduction, turnover of plasma membrane molecules, etc. It is generally accepted that in filamentous fungi, as in yeast, invaginations of the plasma membrane of a small size (up to about 100 nm) are formed in the early stages of endocytosis. These invaginations are surrounded by a rigid actin scaffold – an actin patch, and give rise to small primary endocytic vesicles after scission from the plasma membrane. However, in classical mycological studies, complex large-volume invaginations of the plasma membrane – lomasomes – were described in filamentous fungi. In our time, in a number of filamentous basidiomycetes when tracking endocytosis using styryl fluorescent labels, large invaginations of the plasma membrane have been found, presumably forming endocytic macrovesicles after scission. In this paper, for comparison, large-sized types of endocytosis in animal cells are briefly described. Information about tubular endocytic invaginations in fungi is presented. Three types of large invaginations of the plasma membrane, detected at the TEM level in basidiomycetes, are characterized. The main question this paper addresses is whether or not filamentous fungi do have an analogue of animal macropinocytosis – macrovesicular endocytosis. There are some indications that the answer to this question is yes, but further research is needed. The presence of macrovesicular endocytosis may change the well-established beliefs about the cellular organization of filamentous fungi and the physiology of their nutrition.