Phosphorous is a mineral, and while in the form of inorganic phosphate, it provides living organisms with beneficial nutrients for many types of functions (The bas…c2024). Although it may seem like it, but phosphorus is not phosphate even though the words are used interchangeably. Inorganic phosphate plays a vital role in the mineralization of the skeleton as well as other biological processes throughout the body, such as pH buffering, building cell membranes, and energy metabolism (The bas…c2024; Inorg…c2013). It is very important for inorganic phosphate to remain in homeostasis to be able to maintain a healthy lifestyle. Different issues, both chronic and acute, may occur with any fluctuations of this state of homeostasis. Inorganic phosphate is becoming shown as a significant molecule that can regulate multiple cell functions by changing signal transduction pathways, gene expression, as well as protein abundance in many types of cells (Inorg…c2013).

Inorganic phosphate (Pi) is also very important for cellular metabolism to occur. The reason for this is because Pi helps create phospholipids, which are a form of lipid that is a key part of structural and metabolic tasks within living cells (The bas…c2024). Phospholipids generally consist of one phosphate group and two alcohols, as well as one or two fatty acids. The phosphate group and alcohol are polar and hydrophilic, while the fatty acids are neutral and hydrophobic. Because they do contain these two groups, this makes them important within the membranes (phos…c2024). These phospholipids go on to form nucleotides, the basic building block for nucleic acids, within RNA and DNA, which is needed for cellular energy metabolism to occur (The bas…c2024; Nucl…2024). Enzymatic processes, such as glycolysis require Ip to be present. This is because during the first step of glycolysis, a process called phosphorylation of glucose occurs and Pi is within adenosine triphosphate (ATP), guanosine triphosphate and uridine triphosphate (The bas…c2024).

Multilamellar bodies (MLBs) are cellular organelles found in eukaryotic cells, protozoa, and even more specifically in Dictyostelium discoideum amoebae of lysosomal origin. They are membrane-bound and function within lipid storage and secretion in many different types of cells as well as many other different physiological roles (Lip…c2013). MLBs are made up of circular membrane layers and very often display an electron-dense core (Bio…c2000). They range in size from about 0.1 micrometer to over 2 micrometers. MLBs have been suggested to be a waste disposal system that lets the D. discoideum to remove any bacteria that may be leftover. Although this is only speculation and the true function of MLBs is still not known. There are still studies going on to try to learn more about what these MLBs are and what their function truly is, but it is difficult because they lack certain biological clues. This does not mean that it is impossible to figure out what they are and do. Both amoebae and bacteria contain a specific type of lipid profile. By comparing the make-up of the lipids with the make-up of the MLBs in a purified form, bacteria, and amoebae, it would not make it impossible to figure out where the lipid from MLBs come from. (Lip…c2013). 

The PXo bodies shown in figure 2 all contain different characteristics based off how they are shaped, the size, and the color they take on according to which type of dye or marker is used. For example, in panel a, the green, fluorescent spots, GFP, show N-terminal addition, the red fluorescent, HA, show C-terminal addition, while the blue fluorescent, DAPI, shows where the nucleus is within the cell. Additionally, where the yellow fluorescent shows in the panel is where the green and red fluorescents overlap and tis helps to show where some things are located. The shapes of the PXo-HA in panel one show to be coccobacillus and range in size from small to large. In panel b and c, the PXo protein is more visible, and the shape of the cell is more visible. There also seems to be an increase in PXo bodies compared to the other areas, as shown in panel d. With panels e through k, there are some changes in the type of marker used from how panel a is characterized. For panel e, LysoTracker Red (LysoT) was used as a marker and it is acidic and detects lysosomes, but not exclusively. The organelles within this panel do show levels of acidity because of the presence of yellow spots or overlapping of red and green. In panel f, the marker used is Lamp1, which is also a lysosome marker. This panel does not show a presence of acidity within the organelles and is not associated with a lysosome. Panel g used a marker called Nile Red, which is a lipid dye. This panel shows that PXo is associated with lipids because of the presence of the fluorescent yellow. Panel h uses a Golgi marker called Man II. For this panel, the PXo does not overlap with the Golgi except in trace amounts. Panel i uses a marker called ConA, which is a glycosylation probe. Based off what is shown in this panel, the PXo bodies seem to be glycosylated. Panel j uses P Cho, which is a phosphor lipid tracer, and it shows that there are phospholipids within these organelles. The last panel, k, uses dextran, an endocytosis marker. This panel does not show the presence of an association with endosomes.¹

In figure 3, we can tell that PXo regulates the levels of inorganic phosphate, Pi, within the cytoplasm. This is because of the presence of fluorescent molecules shown in a FRET technique and when exposed to a particular light color, it can transfer energy to another molecule to show a specific color. The blue shows presence of low FRET ratio, or more cyan color than yellow, which represents high levels of Pi present in the cytoplasm. Red shows high FRET ratio, or more yellow than cyan, which represents low levels of Pi in cytoplasm. The average FRET ratio in panel f compared to the normal cells with AHL and supplemental phosphate added have some differences. When PXo is inhibited, the average FTRET ratio lowers showing a fall in phosphate levels within the cytoplasm. This shows that the PXo organelles would pump out phosphate from the cytoplasm. Based off panels d and e in this figure, panel e shows a higher presence of Pi in the cytoplasm because of the amount of cyan in the image. This also shows that there are higher levels shown with a PXo inhibitor.¹

            We can tell that the formation of PXo bodies depends on availability of inorganic phosphate because of what is shown in figure 4. In panel a, normal PXo bodies are shown, panel b contains PXo bodies with the PFA inhibitor, and panel c shows PXo bodies with an RNA based inhibitor, PXo-i. Panel d helps to show the sizes of these bodies in graph form. Based off the graph, the body in panel b is smaller than both panel a and c in size. Panels e through g help to show the amounts of organelles using fluorescents. Green fluorescent protein was used attached to the PXo protein as well as DAPI nuclear stain. In panel f, there is significantly less green with the presence of an inhibitor showing a decrease in the number of organelles. In panel g, there is significantly more green spots with the increase of supplemental phosphate, which shows an increase in the number and size of organelles. Panels j through l show the shape of the PXo bodies in a normal environment versus with an inhibitor added. The average of PXo bodies with the presence of an inhibitor is lower than a normal PXo body and a PXo body with supplemental phosphate added.¹

            Based off the data given in figure 5, we can determine what happens to the types of phospholipids found in PXo bodies when phosphate levels drop in the cytoplasm. Panel d the PXo bodies as a control and contained a 90.6% in phospholipids, while panel e shows PXo bodies with a PFA inhibitor and contained 84.2% phospholipids. In both panels, PE, Phosphatidylethanolamine and PC, Phosphatidylcholine are the two most common phospholipids present. With the decrease of phospholipids with the inhibitor, there was also a decrease in PC, but an increase in other phospholipids that were observed. The amount of PE remained the same in both cases where there was normal conditions and the presence of an inhibitor.¹

            In conclusion, this data does convince me that the PXo bodies form distinct organelles with a unique biochemical function in the cell. This is because of how differently the characteristics of these bodies change depending on the environment that they are in and what they are mixed with. The size and amount of these organelles change depending on what is with them, which shows that they form differently to be able to adapt and function properly. This is shown in many ways throughout all of the figures that were analyzed.¹

Hariri M, Millane G, Guimond M-P, et al (2000) Biogenesis of multilamellar bodies via autophagy. Molecular Biology of the Cell 11:255–268. doi: 10.1091/mbc.11.1.255 

Nucleotide. In: Genome.gov. https://www.genome.gov/genetics-glossary/Nucleotide#:~:text=A%20nucleotide%20is%20the%20basic,)%20and%20thymine%20(T). Accessed 17 Mar 2024 

Paquet VE, Lessire R, Domergue F, et al (2013) Lipid composition of multilamellar bodies secreted by Dictyostelium discoideum reveals their amoebal origin. Eukaryotic Cell 12:1326–1334. doi: 10.1128/ec.00107-13 

Rogers K (2024) Phospholipid. In: Encyclopædia Britannica. https://www.britannica.com/science/phospholipid. Accessed 17 Mar 2024 

Spina A, Sorvillo L, Esposito A, et al (2013) Inorganic phosphate as a signaling molecule: A potential strategy in osteosarcoma treatment. Current Pharmaceutical Design 19:5394–5403. doi: 10.2174/1381612811319300008 

Wagner CA (2023) The basics of phosphate metabolism. Nephrology Dialysis Transplantation 39:190–201. doi: 10.1093/ndt/gfad188 

Xu, C., Xu, J., Tang, H.W., Ericsson, M., Weng, J.H., DiRusso, J., Hu, Y., Ma, W., Asara, J.M., andXu, C., Xu, J., Tang, H.W., Ericsson, M., Weng, J.H., DiRusso, J., Hu, Y., Ma, W., Asara, J.M., and
Perrimon, N. A phosphate-sensing organelle regulates phosphate and tissue homeostasis.
Nature. 2023; 617, 798-806. 10.1038/s41586-023-06039-y.