P-bodies are dynamic ribonucleoprotein granules found in the cell cytoplasm. They are primarily composed of translationally repressed mRNAs and proteins associated with mRNA decay machinery.
What are P-Bodies?
P-bodies (processing bodies) are evolutionarily conserved in eukaryotes and possess the characteristics of liquid droplets. An investigation on proteins related to mRNA decay pathways (decapping and breakdown) has found that P-bodies contain mRNA decay intermediates. This observation has led to an initial hypothesis that P-bodies are basically the cellular locations of mRNA decay.
It was later found that P-bodies are indispensable in regard to mRNA decay. In this context, a recent study has demonstrated that mRNA delay takes place in yeast strains lack P-bodies. Therefore, it is still uncertain what role P-bodies play in mRNA decay. One hypothesis is that they act as storage sites for translationally repressed mRNAs and inactive mRNA decay enzymes.
P-bodies are constitutively associated with proteins that are involved in translational repression and mRNA decay. These proteins include cytoplasmic deadenylase complex, decapping coactivator and enzyme, using oral contraception before clomid decapping activators, and 5’-3’ exoribonuclease.
In addition, RNA-binding proteins are also an integral part of P-bodies. According to a recent study, myosins are also associated with P-bodies, indicating a possible connection between P-bodies and cytoskeleton regulation.
Formation of P-bodies depends on liquid-liquid phase separation (LLPS), which means that these non-membrane cellular compartments are formed by the phase-separation from the cytoplasm. Recently, several fluorescence microscopy studies have revealed that a rapid exchange of components (proteins and RNA) occurs between P-bodies and the cytoplasm, suggesting that P-bodies have dynamic and liquid-like properties.
In addition, P-body dynamics that clearly indicate liquid-like properties are as follows: the spherical morphology of P-bodies due to surface tension as well as the fusion of two P-bodies to form a larger structure that maintains its original round shape. Hexanediol can reversibly dissolve P-bodies, which hinders weak intermolecular interactions.
Concentrations of many P-body-associated proteins with domains containing low complexity sequences and LLPS-associated RNA-binding activities play an essential role in the formation of new P-bodies as well as the maintenance of existing P-bodies. The presence of translationally repressed mRNA and polysome-associated RNA binding proteins is essential for maintaining P-bodies.
Regarding formation of new P-bodies, post-translational modifications of proteins, such as phosphorylation and ubiquitination, are known to have significant contributions. For instance, phosphorylation of decapping enzymes, Dcp1/2, is essential for P-body formation and localization. Moreover, ubiquitination of these enzymes plays an indispensable role in P-body assembly, either independently or by regulating phosphorylation of other P-body-associated proteins. Besides these physiological modifications, certain stress conditions, such as glucose starvation and osmotic stress, are also known to increase the formation of new P-bodies.
Functions of P-Bodies
P-bodies play an essential role in regulating mRNA metabolism. Initially it was thought that P-bodies participate in mRNA decay; however, recent studies using mRNA single-molecule imaging system have clearly demonstrated that mRNA decay events occur in yeast cytoplasm rather than in P-bodies.
In addition, these studies have also revealed that mRNA decay products are present throughout the cytoplasm rather than being stored in P-bodies. All these findings clearly indicate that P-bodies are not directly involved in mRNA decay; they may act as reservoirs to store translationally repressed mRNAs and inactive decapping enzymes.
Stress-induced activation of P-bodies can lead to the inhibition of translation initiation. P-bodies are also known to store proteins and mRNAs associated with nonsense-mediated decay, a special type of mRNA quality control process for degrading mRNAs that terminate translation aberrantly. Moreover, in some cases, P-bodies also contain proteins and microRNAs related to the microRNA repression pathway.
According to many experimental confirmations, mRNAs recirculate between P-bodies and polysomes. One possible mechanism is that mRNAs that cannot participate in translation interact with decapping machinery, and the formed complex is transported to P-bodies from polysomes. Such aggregation of translationally repressed mRNAs inside P-bodies may be essential for maintaining proper amounts of mRNAs within polysomes as well as regulating effective translation of mRNAs into proteins.
- All RNA Content
- What is RNA?
- RNA Structure
- Types of RNA: mRNA, rRNA and tRNA
- RNA Synthesis
Last Updated: Sep 12, 2018
Dr. Sanchari Sinha Dutta
Dr. Sanchari Sinha Dutta is a science communicator who believes in spreading the power of science in every corner of the world. She has a Bachelor of Science (B.Sc.) degree and a Master's of Science (M.Sc.) in biology and human physiology. Following her Master's degree, Sanchari went on to study a Ph.D. in human physiology. She has authored more than 10 original research articles, all of which have been published in world renowned international journals.
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