PXo Bodies: The Newly Discovered Phosphate-Storing Organelle Found in Fruit Flies 

By: Yechezkal Freundlich  |  December 19, 2023

By Yechezkal Freundlich 

Phosphate plays a crucial role in organisms, and it is responsible for several functions within our bodies. It is responsible for bone mineralization and formation––the process that triggers the death of mature cartilage cells that have completed their development — providing room for new bone tissue to form. Additionally, phosphate is an important component of the lipid bilayer of the cell membrane, DNA, RNA, and proteins, maintaining the structure of the cell membrane. Finally, It is an essential electrolyte in the human body, constituting about 1% of the total body weight (NIH). 

In early May of 2023, scientists at the Department of Genetics, in the Blavatnik Institute at Harvard Medical School, led by geneticist Charles (Chiwei) Xu, found a new organelle storing and regulating phosphate. An organelle is a structure within the cell analogous to an organ — specialized components to do specific jobs — allowing the whole cell to function, just like your heart, lungs, and liver do for your whole body. Major organelles include the nucleus, where DNA is kept and translated into RNA; the endoplasmic reticulum, where RNA is translated into proteins; the golgi apparatus, where enzymatic processing of proteins takes place; and the mitochondrion, which powers the cell with ATP and is involved in monitoring and regulating the cell. 

Xu and his colleagues were curious about phosphate’s function in tissue renewal in the guts of fruit flies (Drosophila Melanogaster). They inhibited the absorption of phosphate by feeding the flies phosphonoformic acid. When they stained and imaged the cells of the intestinal lining of the flies, they were surprised to see that the lack of phosphate led to an increase in cell production. Intrigued about why this occurred, Xu and his team investigated a gene called PXo (CG10483), which shares similarities with a mammalian gene responsible for producing a protein that senses phosphate levels. When cells experienced a lack of phosphate, the expression of PXo weakened. Surprisingly, this decrease in gene expression led to a significant increase in cell division. Conversely, when the scientists modified the gene to enhance the production of the PXo protein, cell division slowed down. 

The researchers labeled the PXo proteins with fluorescent markers to track their directory and found that they flowed into a mysterious oval-shaped structure inside the cell that did not seem to be any known organelle. The oval-shaped structure had multiple membrane layers, and the PXo protein transported phosphate across them. The organelle then began converting these phosphates into phospholipids, a crucial component in membrane construction. The fly cells were deprived of phosphate, and the organelles broke apart and released the stored phospholipids into each cell, indicating that they function like reservoirs, Xu told Nature. This is a way that intestinal cells can maintain stable phosphate levels. Xu named this newly discovered organelle PXo bodies. 

The discovery of PXo bodies, this previously unknown phosphate-storing organelle within fruit flies, not only unveils the intricacies of cellular function but also underscores the vastness of unexplored territories within the realm of biology. Charles Xu and his team’s groundbreaking work has illuminated the significance of phosphate in cellular renewal, challenging our existing understanding. 

This revelation emphasizes the importance of investing in scientific research. The pursuit of knowledge, as demonstrated by Xu and his colleagues, leads to unexpected and profound discoveries that have the potential to reshape our comprehension of life processes. PXo bodies, acting as reservoirs for phosphate, showcase the remarkable adaptations that organisms have developed to maintain stability and functionality at the cellular level. 

In a world where there is still so much left to unravel, this study serves as a reminder of the countless mysteries waiting to be solved. The exploration of the unknown not only expands our understanding of the intricate workings of living organisms but also presents new opportunities for advancements in medicine, technology, and beyond. 

Therefore, this discovery should inspire continued support and encouragement for scientific research. By investing in the pursuit of knowledge, we pave the way for innovations that have the potential to improve lives, solve challenges, and deepen our appreciation for the wonders of the natural world. The journey of exploration is ongoing, and each breakthrough brings us closer to comprehending the beauty and complexity of our world.