Abstract
In highly polarised cells, like fungal hyphae, early endosomes function in both endocytosis as well as long-distance transport of various cargo including mRNA and protein complexes. However, knowledge on the crosstalk between these seemingly different trafficking processes is scarce. Here, we demonstrate that the ESCRT regulator Did2 coordinates endosomal transport in fungal hyphae of Ustilago maydis. Loss of Did2 results in defective vacuolar targeting, less processive long-distance transport and abnormal shuttling of early endosomes. Importantly, the late endosomal protein Rab7 and vacuolar protease Prc1 exhibit increased shuttling on these aberrant endosomes suggesting defects in endosomal maturation and identity. Consistently, molecular motors fail to attach efficiently explaining the disturbed processive movement. Furthermore, the endosomal mRNP linker protein Upa1 is hardly present on endosomes resulting in defects in long-distance mRNA transport. In conclusion, the ESCRT regulator Did2 coordinates precise maturation of endosomes and thus provides the correct membrane identity for efficient endosomal long-distance transport.
Highlights
Endocytosis constitutes a fundamental eukaryotic mechanism that is required for the regulation of important cellular processes, e.g. establishment of cell polarity at the plasma membrane
Consistent with findings in S. cerevisiae, Vps60 and Did2 were dispensable for budding growth, but loss of both proteins resulted in reduced resistance against cell wall stress (S2A and S2B Fig) [38]
Since loss of Did2 induced an overall stronger phenotype, which in some aspects closely resembled loss of Rrm4, we focused on the ESCRT-III regulator Did2
Summary
Endocytosis constitutes a fundamental eukaryotic mechanism that is required for the regulation of important cellular processes, e.g. establishment of cell polarity at the plasma membrane. Endocytosis mediates, for example, the removal of plasma membrane proteins from the cell surface for subsequent degradation in the lysosome/vacuole. After internalisation, membrane proteins are sorted into early endosomes, which mature to late endosomes before they are targeted to the lysosomal/vacuolar compartment [1]. A key component of endosomal maturation is the ESCRT complex (endosomal sorting complex required for transport), a highly evolutionary conserved multi-protein complex [2,3,4,5]. One function of this sophisticated membrane remodelling machinery is the formation of intraluminal vesicles within endosomes, resulting in the formation of multivesicular bodies. Thereby, endocytosed transmembrane proteins such as receptors are sorted for degradation in the lysosome/vacuole [3, 4]
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