Hemifusomes

What is the hemifusome?

Last summer, researchers at the University of Virginia School of Medicine and the National Institutes of Health announced the discovery of a new organelle inside human cells called the hemifusome. This finding is especially significant because the basic model of the human cell has remained unchanged for decades. Discovering a new organelle indicates that there are still gaps in our understanding of how cells function.

The hemifusome plays an important role in cellular “housekeeping,” meaning that it helps cells sort, recycle, and transport materials internally. Scientists often compare vesicles to delivery tricks inside the cell, and the hemifusome acts like a loading dock where these materials are transferred and processed. Their role is crucial as it helps the body address diseases caused by failures in cellular transport. 

Structure

The hemifusome is made up of two vesicles that are partially fused together. One vesicle is larger and contains granular material, while the other is smaller and more translucent. They are connected by a structure called a hemifusion diaphragm: a membrane that was previously overlooked because scientists believed it would be too unstable to exist. This diaphragm is much larger than the typical membrane fusion structures, demonstrating that the hemifusome is stable rather than temporary. Scientists believe that  it forms through a process called reverse fusion. In this process, the smaller vesicle starts outside the larger one, then folds inward, eventually forming internal vesicles. This explains how multivesicular bodies that are important for immune function and cell communication are created. 

Discovery

One reason hemifusomes were not discovered earlier were because of limitations in older imaging techniques. Traditional microscopes could not capture these fast and delicate processes. The breakthrough came as a result of cryo-electron tomography, a method that freezes cells in time and allows scientists to see structures in much greater detail. 

Using this technology, researchers observed hemifusomes actively forming vesicles. They also found that these structures may make up a noticeable portion of vesicular organelles, suggesting that they are more common than previously thought. This discovery also challenges the belief that vesicles form through protein-based pathways like ESCRT. Instead, hemifusomes rely more on lipid-based membrane remodeling. 

Future potential in medicine

The discovery of the hemifusomes can significantly impact medicine, specifically in understanding rare genetic disorders. One example is the Hermansky-Pudlak syndrome, a condition linked to problems in cell transport. Since hemifusomes are directly involved in moving and processing materials within the cell, they can help explain what goes wrong in such diseases. 

Researchers are still in the early stages of studying this organelle. Many questions are still being investigated, including how hemifusomes may behave in healthy cells as opposed to diseased cells and what triggers their formation. However, this discovery opens up a new pathway for studying how cells function. In the future, it could lead to targeted therapies that address the root causes of genetic diseases, rather than just treating symptoms. 

References:

 “The Hemifusome: Cell Biology’s Latest Discovery - the YU Observer.” The YU Observer, 23 Dec. 2025, yuobserver.org/2025/12/the-hemifusome-cell-biologys-latest-discovery/. Accessed 29 Mar. 2026.

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“Meet the Hemifusome: A New Organelle with Big Impact.” Drug Target Review, 2025, www.drugtargetreview.com/news/167964/meet-the-hemifusome-a-new-organelle-with-big-impact/.

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