Amazing stuff! It again confirms that we still know so little!
How is this possible that at the end of the first quarter of the 21st century that such a common and long-lived vesicle was not discovered earlier? The cell is probably one of the most researched objects you can think of. The single cell was discovered by Robert Hooke in 1665.
What else are we missing?
"The discovery of an unknown organelle inside our cells could open the door to new treatments for devastating inherited diseases.
The organelle, a type of specialized structure, has been dubbed a "hemifusome" by its discoverers ... This little organelle has a big job helping our cells sort, recycle and discard important cargo within themselves, the scientists say. The new discovery could help scientists better understand what goes wrong in genetic conditions that disrupt these essential housekeeping functions. ...
“This is like discovering a new recycling center inside the cell,” ...
“It’s exciting because finding something truly new inside cells is rare – and it gives us a whole new path to explore.” ..."
From the abstract:
"The pleiomorphic structure and dynamic behavior of cellular endomembrane systems have been extensively studied using classical electron microscopy. However, fixation and staining constraints limit the in situ visualization of transient interactions, such as membrane fusion, scission, and intraluminal vesicle formation, potentially overlooking intermediate structures like membrane hemifusion.
Using in situ cryo-electron tomography in four mammalian cell lines, we identify heterotypic hemifused vesicles featuring an extended hemifusion diaphragm consistently associated with a 42-nanometer proteolipid nanodroplet (PND).
We designate these vesicular organelle complexes as “hemifusomes.” Hemifusomes constitute up to 10% of vesicular organelles at the cell periphery but do not engage in canonical endocytic pathways.
These structures exhibit diverse conformations and frequently contain intraluminal vesicles.
Building on the continuum of related morphologies observed, we propose that hemifusomes serve as platforms for vesicular biogenesis, mediated by the PND. These findings provide direct in situ evidence of long-lived hemifused vesicle complexes and introduce an ESCRT-independent model for multivesicular body (MVB) formation."
Previously unknown 'loading dock' found inside human cells
Scientists Discover Unknown Organelle Inside Our Cells (original news release)
Hemifusomes and interacting proteolipid nanodroplets mediate multi-vesicular body formation (open access)
Cryo-electron tomography observation of hemifused vesicles at the leading edge of cultured cells.
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