Rivier-Cordey, A.-S. | bioRxiv Science

bioRxiv2025

Evolutionarily diverged on-switch for actin assembly in fungal endocytosis

Clathrin-mediated endocytosis is a conserved eukaryotic trafficking process where an Arp2/3 complex nucleated branched actin network provides force for vesicle formation. The mechanisms that initiate endocytic actin assembly are incompletely understood. In the fission yeast, Schizosaccharomyces pombe, actin assembly is initiated by Dip1, an Arp2/3 activator. In the budding yeast, Saccharomyces cerevisiae, the initiation of actin assembly has remained a mystery. Here we show that S. cerevisiae Ldb17, the homolog of Dip1, functions as an on-switch for endocytic actin assembly. Unexpectedly, the regulation of Ldb17 is more complicated than that of constitutively active Dip1. Ldb17 is controlled by a coat protein, Sla1, via separate recruitment and activation steps. This regulation was likely lost in the S. pombe lineage and this simplification may be related to other changes in actin assembly between these species. Our findings add a key missing piece in the understanding of endocytosis in S. cerevisiae and reveal an intriguing evolutionary tinkering of the actin on-switch.

cell biology↗

bioRxiv2024

An evolutionary cell biology perspective into the diverging mechanisms of clathrin-mediated endocytosis in dikarya fungi

Clathrin-mediated endocytosis is an ancient eukaryotic trafficking pathway, which transports plasma membrane and associated cargo into the cell and is involved in numerous cell- and tissue-level processes. Cargo selection and clathrin-coated vesicle formation is mediated by over 60 proteins that assemble in a regular and sequential manner at the plasma membrane. Decades of endocytosis studies have followed the tenet that uncovering the conserved core molecular mechanisms is sufficient to understand a cellular process. However, this approach also revealed a number of cell type or species-related variations that challenge a universal conserved, core mechanism. In this paper, we refocus on the endocytic diversity to understand how evolution shapes endocytic mechanisms. We define a comparative evolutionary cell biology approach that uses dikarya fungi as a model clade and live-cell fluorescence microscopy to study endocytosis dynamics in three species: Saccharomyces cerevisiae, Schizosaccharomyces pombe and Ustilago maydis. Our results quantitatively define several phenotypic differences between the species. We uncover several differences that impact the endocytic early phase, the protein assembly order, actin regulation, membrane invagination and scission. These findings demonstrate a mosaic evolution of endocytic traits, suggest ancestral states and direction of changes. We also investigate the phenotypic plasticity and robustness against environmental conditions. Lastly, we demonstrate that relatively minor evolutionary changes can majorly impact endocytic phenotypes. These studies force an appreciation of endocytic variation as not auxiliary, but vital to mechanistic understanding of this conserved cellular pathway.

cell biology↗