For the first time, a new organelle has been found in an animal cell. These organelles, called PXo bodies, interact with inorganic phosphate in a way previously only seen in bacteria, plant and yeast cells, but has now appeared in one of the most studied animals on Earth.
The fruit fly Drosophila melanogaster is frequently the subject of scientific research, and its only competitor may be the ubiquitous roundworm Caenorhabditis elegans. Despite being under the scrutiny of scientists for over a century, fruit flies still seem to hold some secrets.
A new discovery shows a type of organelle, which are miniature membrane-bound structures that perform a specific function in a cell. Nuclei that store genetic information, ribosomes that assemble proteins, and mitochondria, the “powerhouse of the cell,” can be cited as examples to explain what organelles are.
When the researchers tried to stain an unidentified oval-shaped structure in D. melanogaster cells, they realized they were dealing with a new organelle. When they noticed that a PXo protein known to carry inorganic phosphate (Pi) was trapped inside these mysterious spheres, they were studying the object closely as they were investigating the role of Pi in metabolism and signal transduction in animal tissues.
When none of their staining efforts were successful, they realized they had found an entirely new organelle for animal cells. In view of their association with PXo proteins, these new bodies were named PXo bodies.
Using electron microscopy, the researchers deciphered the structures of the PXo bodies and found that they are composed of spiral rings covered with Pi transport proteins. These structures effectively pulled Pi from the cytoplasm of the cell and stored it, which is essential for cell functions involved in metabolism and DNA synthesis.
When they started to play with the amount of Pi in fruit fly cells, they found that not having enough Pi led to excessive cell growth in the digestive tract of their body. This also triggered the PXo to stop shifting too many Pi’s into storage, and the PXo bodies smashing some of their stock, possibly as a way to free it up for cell functions.
While the findings shed light on the importance of intracellular phosphate regulation in animal cells, about which we historically know little, the researchers hope that following the breakthrough with this initial discovery, we may begin to make up for this shortfall.
“Given the paucity of knowledge about cytosolic Pi regulation in animal cells, our findings could have broad implications and open up new avenues to study Pi metabolism and signaling,” the researchers write in conclusion of their paper.
The study was published in the journal Nature.
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