Coordination of Actin and Endocytosis During Hyphal Extension

Filamentous fungi rely on sustained polarized growth to invade substrates, explore environments, and establish complex multicellular structures. This growth is supported by a spatially organized endocytic system that retrieves membrane and protein components from the plasma membrane while maintaining a dedicated zone for exocytosis at the apex. Central to this process is the subapical endocytic collar—a band of dynamic cortical patches enriched in actin-associated proteins and endocytic adaptors. In contrast to yeast, where endocytosis occurs diffusely and is largely clathrin-mediated, filamentous fungi concentrate endocytic activity at the subapical collar—where it proceeds via clathrin-independent, AP-2-mediated mechanisms—while retaining clathrin-dependent patches elsewhere along the hyphal surface. Endocytic vesicles formed at the collar are trafficked via early endosomes and returned to the apex or targeted for degradation, enabling membrane homeostasis and recycling of polarity factors. This chapter reviews the spatial organization, molecular machinery, and functional significance of collar-based endocytosis in filamentous fungi, highlighting its role in polarized growth and its integration with cytoskeletal and vesicle trafficking systems. We also discuss open questions and emerging methods that are reshaping our understanding of this specialized endocytic pathway.