The cell nucleus, which contains the DNA, the mitochondria, which act as a kind of energy production factory … The list of “organelles”, that is, the differentiated structures contained in the cells, could be expanded by the inclusion of a new element, so far completely unknown. The authors of a study published in the journal Nature (05/03/2023) called it “PXo body”.
According to the authors who described it, this organelle would be involved in the regulation of phosphate. A nutrient that is at the heart of several key processes in cells, such as metabolism, energy storage and the synthesis of genetic material.
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While plant and fungal cells (plants or fungi) have organelles that specifically serve to regulate phosphate, nothing comparable has been identified in the animal kingdom. The discovery of this structure is all the more surprising given that it was made in one of the animal models most studied in the laboratory by biologists worldwide, namely Drosophila or the fruit fly.
Do humans have PXo bodies in their cells?
“It’s quite amazing that every day we continue to discover things in model organisms that no one knew before,” Laurent Seroude, a geneticist at Canada’s Queen’s University, told Live Science. The researcher, who was not involved in the study, points out that discoveries made in model organisms are often transferrable to other species. Therefore, in his opinion, it is possible that other animals, including humans, are carriers of this unknown organelle – which, however, still has to be verified with the help of further work.
In the fly gut, PXo bodies bind phosphate from food and regulate the availability of this nutrient to cells, the authors write in the study.
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Along with his colleagues, Professor Charles (Chiwei) tried the fly.
By feeding the insects meals low in phosphate or giving them a drug that inhibits uptake of this nutrient, the team noticed a phenomenon that seems paradoxical. Despite the low phosphate levels, the cells lining the animal’s intestines multiplied rapidly. The same is true when the team suppressed the expression of the PXo protein, which is nevertheless known to control the transport of phosphate (chemical symbol: P) within cells.
The scientists then came up with the idea of fusing the protein with a fluorescent substance to localize its presence in the fly’s cells. Under the microscope, they found that it accumulated in oval structures. Mitochondria maybe? While the researchers tested different types of dyes associated with known organelles in cells, none worked. The only explanation, in their opinion, is that it was a new organelle that had never been described before.
A discovery associated with more efficient microscopes
Professor Xu and his colleagues dubbed these new organelles PXo bodies and used electron microscopy to study their architecture. They thus observed spiral membranes dotted with PXo proteins that transport phosphate from the cytoplasm – the fluid that surrounds the organelles – to the organelle for storage, thereby regulating the amount of phosphate available for cell functions.
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“I wouldn’t say we discovered this organelle out of nowhere,” the first author qualified Live Science. Rather, he believes that cutting-edge research techniques have enabled him to characterize in detail the membrane spirals, which he says have been previously neglected. Thus, this discovery makes it possible to see the images of an article published 50 years ago (Leslie P. Gartner, 1973) in a new light, at a time when microscopy tools were much less developed than they are today.
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