Hemifusomes are intracellular organelles first described in 2025 by researchers at the National Institutes of Health and the University of Virginia School of Medicine. [1] [2] Discovered using in situ cryo-electron tomography, hemifusomes are heterotypic vesicular complexes marked by a persistent hemifusion diaphragm and a characteristic 42-nanometer proteolipid nanodroplet (PND). These organelles account for up to 10% of vesicular structures at the cell periphery and often contain intraluminal vesicles, but they do not participate in conventional endocytic pathways.
Hemifusomes are proposed to act as platforms for vesicle biogenesis via an ESCRT-independent mechanism (Endosomal Sorting Complexes Required for Transport -independent mechanism) for multivesicular body formation. Their shape has been likened to a snowman wearing a scarf.
