In cellular biology, P-bodies, or processing bodies, are distinct foci formed by phase separation within the cytoplasm of a eukaryotic cell consisting of many enzymes involved in mRNA turnover. [1] P-bodies are highly conserved structures and have been observed in somatic cells originating from vertebrates and invertebrates, plants and yeast. To date, P-bodies have been demonstrated to play fundamental roles in general mRNA decay, nonsense-mediated mRNA decay, adenylate-uridylate-rich element mediated mRNA decay, and microRNA (miRNA) induced mRNA silencing. [2] Not all mRNAs which enter P-bodies are degraded, as it has been demonstrated that some mRNAs can exit P-bodies and re-initiate translation. [3] [4] Purification and sequencing of the mRNA from purified processing bodies showed that these mRNAs are largely translationally repressed upstream of translation initiation and are protected from 5' mRNA decay. [5]
P-bodies were originally proposed to be the sites of mRNA degradation in the cell and involved in decapping and digestion of mRNAs earmarked for destruction. [6] [7] Later work called this into question suggesting P bodies store mRNA until needed for translation. [8] [5] [9]
In neurons, P-bodies are moved by motor proteins in response to stimulation. This is likely tied to local translation in dendrites. [10]
P-bodies were first described in the scientific literature by Bashkirov et al. [11] in 1997, in which they describe "small granules… discrete, prominent foci" as the cytoplasmic location of the mouse exoribonuclease mXrn1p. It wasn’t until 2002 that a glimpse into the nature and importance of these cytoplasmic foci was published., [12] [13] [14] when researchers demonstrated that multiple proteins involved with mRNA degradation localize to the foci. Their importance was recognized after experimental evidence was obtained pointing to P-bodies as the sites of mRNA degradation in the cell. [7] The researchers named these structures processing bodies or "P bodies". During this time, many descriptive names were used also to identify the processing bodies, including "GW-bodies" and "decapping-bodies"; however "P-bodies" was the term chosen and is now widely used and accepted in the scientific literature. [7] Recently evidence has been presented suggesting that GW-bodies and P-bodies may in fact be different cellular components. [15] The evidence being that GW182 and Ago2, both associated with miRNA gene silencing, are found exclusively in multivesicular bodies or GW-bodies and are not localized to P-bodies. Also of note, P-bodies are not equivalent to stress granules and they contain largely non-overlapping proteins. [5] The two structures support overlapping cellular functions but generally occur under different stimuli. Hoyle et al. suggests a novel site termed EGP bodies, or stress granules, may be responsible for mRNA storage as these sites lack the decapping enzyme. [16]
microRNA mediated repression occurs in two ways, either by translational repression or stimulating mRNA decay. miRNA recruit the RISC complex to the mRNA to which they are bound. The link to P-bodies comes by the fact that many, if not most, of the proteins necessary for miRNA gene silencing are localized to P-bodies, as reviewed by Kulkarni et al. (2010). [2] [17] [18] [19] [20] These proteins include, but are not limited to, the scaffold protein GW182, Argonaute (Ago), decapping enzymes and RNA helicases. The current evidence points toward P-bodies as being scaffolding centers of miRNA function, especially due to the evidence that a knock down of GW182 disrupts P-body formation. However, there remain many unanswered questions about P-bodies and their relationship to miRNA activity. Specifically, it is unknown whether there is a context dependent (stress state versus normal) specificity to the P-body's mechanism of action. Based on the evidence that P-bodies sometimes are the site of mRNA decay and sometimes the mRNA can exit the P-bodies and re-initiate translation, the question remains of what controls this switch. Another ambiguous point to be addressed is whether the proteins that localize to P-bodies are actively functioning in the miRNA gene silencing process or whether they are merely on standby.
In 2017, a new method to purify processing bodies was published. [5] Hubstenberger et al. used fluorescence-activated particle sorting (a method based on the ideas of fluorescence-activated cell sorting) to purify processing bodies from human epithelial cells. From these purified processing bodies they were able to use mass spectrometry and RNA sequencing to determine which proteins and RNAs are found in processing bodies, respectively. This study identified 125 proteins that are significantly associated with processing bodies. [5] Notably this work provided the most compelling evidence up to this date that P-bodies might not be the sites of degradation in the cell and instead used for storage of translationally repressed mRNA. This observation was further supported by single molecule imaging of mRNA by the Chao group in 2017. [9]
In 2018, Youn et al. took a proximity labeling approach called BioID to identify and predict the processing body proteome. [21] They engineered cells to express several processing body-localized proteins as fusion proteins with the BirA* enzyme. When the cells are incubated with biotin, BirA* will biotinylate proteins that are nearby, thus tagging the proteins within processing bodies with a biotin tag. Streptavidin was then used to isolate the tagged proteins and mass spectrometry to identify them. Using this approach, Youn et al. identified 42 proteins that localize to processing bodies. [21]
Gene ID | Protein | References | Also found in stress granules? |
---|---|---|---|
MOV10 | MOV10 | [5] [21] | Yes |
EDC3 | EDC3 | [21] | Yes |
EDC4 | EDC4 | [5] | Yes |
ZCCHC11 | TUT4 | [5] | No |
DHX9 | DHX9 | [5] | No |
RPS27A | RS27A | [5] | No |
UPF1 | RENT1 | [5] | Yes |
ZCCHC3 | ZCHC3 | [5] | No |
SMARCA5 | SMCA5 | [5] | No |
TOP2A | TOP2A | [5] | No |
HSPA2 | HSP72 | [5] | No |
SPTAN1 | SPTN1 | [5] | No |
SMC1A | SMC1A | [5] | No |
ACTBL2 | ACTBL | [5] | Yes |
SPTBN1 | SPTB2 | [5] | No |
DHX15 | DHX15 | [5] | No |
ARG1 | ARGI1 | [5] | No |
TOP2B | TOP2B | [5] | No |
APOBEC3F | ABC3F | [5] | No |
NOP58 | NOP58 | [5] | Yes |
RPF2 | RPF2 | [5] | No |
S100A9 | S100A9 | [5] | Yes |
DDX41 | DDX41 | [5] | No |
KIF23 | KIF23 | [5] | Yes |
AZGP1 | ZA2G | [5] | No |
DDX50 | DDX50 | [5] | Yes |
SERPINB3 | SPB3 | [5] | No |
SBSN | SBSN | [5] | No |
BAZ1B | BAZ1B | [5] | No |
MYO1C | MYO1C | [5] | No |
EIF4A3 | IF4A3 | [5] | No |
SERPINB12 | SPB12 | [5] | No |
EFTUD2 | U5S1 | [5] | No |
RBM15B | RB15B | [5] | No |
AGO2 | AGO2 | [5] | Yes |
MYH10 | MYH10 | [5] | No |
DDX10 | DDX10 | [5] | No |
FABP5 | FABP5 | [5] | No |
SLC25A5 | ADT2 | [5] | No |
DMKN | DMKN | [5] | No |
DCP2 | DCP2 | [5] [13] [14] [22] | No |
S100A8 | S10A8 | [5] | No |
NCBP1 | NCBP1 | [5] | No |
YTHDC2 | YTDC2 | [5] | No |
NOL6 | NOL6 | [5] | No |
XAB2 | SYF1 | [5] | No |
PUF60 | PUF60 | [5] | No |
RBM19 | RBM19 | [5] | No |
WDR33 | WDR33 | [5] | No |
PNRC1 | PNRC1 | [5] | No |
SLC25A6 | ADT3 | [5] | No |
MCM7 | MCM7 | [5] | Yes |
GSDMA | GSDMA | [5] | No |
HSPB1 | HSPB1 | [5] | Yes |
LYZ | LYSC | [5] | No |
DHX30 | DHX30 | [5] | Yes |
BRIX1 | BRX1 | [5] | No |
MEX3A | MEX3A | [5] | Yes |
MSI1 | MSI1H | [5] | Yes |
RBM25 | RBM25 | [5] | No |
UTP11L | UTP11 | [5] | No |
UTP15 | UTP15 | [5] | No |
SMG7 | SMG7 | [5] [21] | Yes |
AGO1 | AGO1 | [5] | Yes |
LGALS7 | LEG7 | [5] | No |
MYO1D | MYO1D | [5] | No |
XRCC5 | XRCC5 | [5] | No |
DDX6 | DDX6/p54/RCK | [5] [21] [23] [24] | Yes |
ZC3HAV1 | ZCCHV | [5] | Yes |
DDX27 | DDX27 | [5] | No |
NUMA1 | NUMA1 | [5] | No |
DSG1 | DSG1 | [5] | No |
NOP56 | NOP56 | [5] | No |
LSM14B | LS14B | [5] | Yes |
EIF4E2 | EIF4E2 | [21] | Yes |
EIF4ENIF1 | 4ET | [5] [21] | Yes |
LSM14A | LS14A | [5] [21] | Yes |
IGF2BP2 | IF2B2 | [5] | Yes |
DDX21 | DDX21 | [5] | Yes |
DSC1 | DSC1 | [5] | No |
NKRF | NKRF | [5] | No |
DCP1B | DCP1B | [5] [24] | No |
SMC3 | SMC3 | [5] | No |
RPS3 | RS3 | [5] | Yes |
PUM1 | PUM1 | [5] | Yes |
PIP | PIP | [5] | No |
RPL26 | RL26 | [5] | No |
GTPBP4 | NOG1 | [5] | No |
PES1 | PESC | [5] | No |
DCP1A | DCP1A | [5] [13] [14] [22] [20] | No |
ELAVL2 | ELAV2 | [5] | Yes |
IGLC2 | LAC2 | [5] | No |
IGF2BP1 | IF2B1 | [5] | Yes |
RPS16 | RS16 | [5] | No |
HNRNPU | HNRPU | [5] | No |
IGF2BP3 | IF2B3 | [5] | Yes |
SF3B1 | SF3B1 | [5] | No |
STAU2 | STAU2 | [5] | Yes |
ZFR | ZFR | [5] | No |
HNRNPM | HNRPM | [5] | No |
ELAVL1 | ELAV1 | [5] | Yes |
FAM120A | F120A | [5] | Yes |
STRBP | STRBP | [5] | No |
RBM15 | RBM15 | [5] | No |
LMNB2 | LMNB2 | [5] | No |
NIFK | MK67I | [5] | No |
TF | TRFE | [5] | No |
HNRNPR | HNRPR | [5] | No |
LMNB1 | LMNB1 | [5] | No |
ILF2 | ILF2 | [5] | No |
H2AFY | H2AY | [5] | No |
RBM28 | RBM28 | [5] | No |
MATR3 | MATR3 | [5] | No |
SYNCRIP | HNRPQ | [5] | Yes |
HNRNPCL1 | HNRCL | [5] | No |
APOA1 | APOA1 | [5] | No |
XRCC6 | XRCC6 | [5] | No |
RPS4X | RS4X | [5] | No |
DDX18 | DDX18 | [5] | No |
ILF3 | ILF3 | [5] | Yes |
SAFB2 | SAFB2 | [5] | Yes |
RBMX | RBMX | [5] | No |
ATAD3A | ATD3A | [5] | Yes |
HNRNPC | HNRPC | [5] | No |
RBMXL1 | RMXL1 | [5] | No |
IMMT | IMMT | [5] | No |
ALB | ALBU | [5] | No |
CSNK1D | CK1𝛿 | [23] | No |
XRN1 | XRN1 | [11] [13] [21] [22] | Yes |
TNRC6A | GW182 | [21] [22] [12] [20] [25] | Yes |
TNRC6B | TNRC6B | [21] | Yes |
TNRC6C | TNRC6C | [21] | Yes |
LSM4 | LSM4 | [20] [13] | No |
LSM1 | LSM1 | [13] | No |
LSM2 | LSM2 | [13] | No |
LSM3 | LSM3 | [13] [24] | Yes |
LSM5 | LSM5 | [13] | No |
LSM6 | LSM6 | [13] | No |
LSM7 | LSM7 | [13] | No |
CNOT1 | CCR4/CNOT1 | [24] [21] | Yes |
CNOT10 | CNOT10 | [21] | Yes |
CNOT11 | CNOT11 | [21] | Yes |
CNOT2 | CNOT2 | [21] | Yes |
CNOT3 | CNOT3 | [21] | Yes |
CNOT4 | CNOT4 | [21] | Yes |
CNOT6 | CNOT6 | [21] | Yes |
CNOT6L | CNOT6L | [21] | Yes |
CNOT7 | CNOT7 | [21] | Yes |
CNOT8 | CNOT8 | [21] | Yes |
CNOT9 | CNOT9 | [21] | No |
RBFOX1 | RBFOX1 | [26] | Yes |
ANKHD1 | ANKHD1 | [21] | Yes |
ANKRD17 | ANKRD17 | [21] | Yes |
BTG3 | BTG3 | [21] | Yes |
CEP192 | CEP192 | [21] | No |
CPEB4 | CPEB4 | [21] | Yes |
CPVL | CPVL | [21] | Yes |
DIS3L | DIS3L | [21] | No |
DVL3 | DVL3 | [21] | No |
FAM193A | FAM193A | [21] | No |
GIGYF2 | GIGYF2 | [21] | Yes |
HELZ | HELZ | [21] | Yes |
KIAA0232 | KIAA0232 | [21] | Yes |
KIAA0355 | KIAA0355 | [21] | No |
MARF1 | MARF1 | [21] | Yes |
N4BP2 | N4BP2 | [21] | No |
PATL1 | PATL1 | [21] | Yes |
RNF219 | RNF219 | [21] | Yes |
ST7 | ST7 | [21] | Yes |
TMEM131 | TMEM131 | [21] | Yes |
TNKS1BP1 | TNKS1BP1 | [21] | Yes |
TTC17 | TTC17 | [21] | Yes |
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein.
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, proteins or non-coding RNA, and ultimately affect a phenotype. These products are often proteins, but in non-protein-coding genes such as transfer RNA (tRNA) and small nuclear RNA (snRNA), the product is a functional non-coding RNA. The process of gene expression is used by all known life—eukaryotes, prokaryotes, and utilized by viruses—to generate the macromolecular machinery for life.
Polyadenylation is the addition of a poly(A) tail to an RNA transcript, typically a messenger RNA (mRNA). The poly(A) tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In eukaryotes, polyadenylation is part of the process that produces mature mRNA for translation. In many bacteria, the poly(A) tail promotes degradation of the mRNA. It, therefore, forms part of the larger process of gene expression.
In cell biology, a granule is a small particle barely visible by light microscopy. The term is most often used to describe a secretory vesicle containing important components of cell phyisology. Examples of granules include granulocytes, platelet granules, insulin granules, germane granules, starch granules, and stress granules.
In the cellular biology, stress granules are biomolecular condensates in the cytosol composed of proteins and RNA that assemble into 0.1–2 μm membraneless organelles when the cell is under stress. The mRNA molecules found in stress granules are stalled translation pre-initiation complexes associated with 40S ribosomal subunits, translation initiation factors, poly(A)+ mRNA and RNA-binding proteins (RBPs). While they are membraneless organelles, stress granules have been proposed to be associated with the endoplasmatic reticulum. There are also nuclear stress granules. This article is about the cytosolic variety.
The exosome complex is a multi-protein intracellular complex capable of degrading various types of RNA molecules. Exosome complexes are found in both eukaryotic cells and archaea, while in bacteria a simpler complex called the degradosome carries out similar functions.
5′-3′ exoribonuclease 1 (Xrn1) is a protein that in humans is encoded by the XRN1 gene. Xrn1 hydrolyses RNA in the 5′ to 3′ direction.
Polyadenylate-binding protein 1 is a protein that in humans is encoded by the PABPC1 gene. The protein PABP1 binds mRNA and facilitates a variety of functions such as transport into and out of the nucleus, degradation, translation, and stability. There are two separate PABP1 proteins, one which is located in the nucleus (PABPN1) and the other which is found in the cytoplasm (PABPC1). The location of PABP1 affects the role of that protein and its function with RNA.
Poly(A)-specific ribonuclease (PARN), also known as polyadenylate-specific ribonuclease or deadenylating nuclease (DAN), is an enzyme that in humans is encoded by the PARN gene.
Regulator of nonsense transcripts 2 is a protein that in humans is encoded by the UPF2 gene.
Trinucleotide repeat-containing gene 6A protein is a protein that in humans is encoded by the TNRC6A gene.
mRNA-decapping enzyme 2 is a protein that in humans is encoded by the DCP2 gene.
mRNA-decapping enzyme 1A is a protein that in humans is encoded by the DCP1A gene.
mRNA-decapping enzyme 1B is a protein that in humans is encoded by the DCP1B gene.
Post-transcriptional regulation is the control of gene expression at the RNA level. It occurs once the RNA polymerase has been attached to the gene's promoter and is synthesizing the nucleotide sequence. Therefore, as the name indicates, it occurs between the transcription phase and the translation phase of gene expression. These controls are critical for the regulation of many genes across human tissues. It also plays a big role in cell physiology, being implicated in pathologies such as cancer and neurodegenerative diseases.
The process of messenger RNA decapping consists of hydrolysis of the 5' cap structure on the RNA exposing a 5' monophosphate. In eukaryotes, this 5' monophosphate is a substrate for the 5' exonuclease Xrn1 and the mRNA is quickly destroyed. There are many situations which may lead to the removal of the cap, some of which are discussed below.
The mRNA decapping complex is a protein complex in eukaryotic cells responsible for removal of the 5' cap. The active enzyme of the decapping complex is the bilobed Nudix family enzyme Dcp2, which hydrolyzes 5' cap and releases 7mGDP and a 5'-monophosphorylated mRNA. This decapped mRNA is inhibited for translation and will be degraded by exonucleases. The core decapping complex is conserved in eukaryotes. Dcp2 is activated by Decapping Protein 1 (Dcp1) and in higher eukaryotes joined by the scaffold protein VCS. Together with many other accessory proteins, the decapping complex assembles in P-bodies in the cytoplasm.
Cryptic unstable transcripts (CUTs) are a subset of non-coding RNAs (ncRNAs) that are produced from intergenic and intragenic regions. CUTs were first observed in S. cerevisiae yeast models and are found in most eukaryotes. Some basic characteristics of CUTs include a length of around 200–800 base pairs, a 5' cap, poly-adenylated tail, and rapid degradation due to the combined activity of poly-adenylating polymerases and exosome complexes. CUT transcription occurs through RNA Polymerase II and initiates from nucleosome-depleted regions, often in an antisense orientation. To date, CUTs have a relatively uncharacterized function but have been implicated in a number of putative gene regulation and silencing pathways. Thousands of loci leading to the generation of CUTs have been described in the yeast genome. Additionally, stable uncharacterized transcripts, or SUTs, have also been detected in cells and bear many similarities to CUTs but are not degraded through the same pathways.
In cellular biology, a chromatoid body is a dense structure in the cytoplasm of male germ cells. It is composed mainly of RNA and RNA-binding proteins and is thus a type of RNP granule. Chromatoid body-like granules first appear in spermatocytes and condense into a single granule in round spermatids. The structure disappears again when spermatids start to elongate. The chromatoid body is crucial for spermatogenesis, but its exact role in the process is not known. Following significant strides in the understanding of small non-coding RNA mediated gene regulation and Piwi-interacting RNA (piRNA) and their roles in germline development, the function of chromatoid bodies (CBs) has been somewhat elucidated. However, due to similarities with RNP granules found in somatic cells – such as stress granules and processing bodies – chromatoid body is thought to be involved in post-transcriptional regulation of gene expression. Postmeiotic germ cell differentiation induces the accumulation of piRNAs and proteins of piRNA machinery along with several distinct RNA regulator proteins. Although evidence suggests CB involvement in mRNA regulation and small RNA mediated gene regulation, the mechanism of action remains obscure.
Roy R. Parker is a biochemist who has been an active investigator in science since the 1970s. He is currently a Distinguished Professor of Chemistry and Biochemistry and Cech-Leinwand Endowed Chair of Biochemistry at the University of Colorado Boulder. Throughout his life, Parker has contributed a vast degree of knowledge to research and studies of biochemistry. His current focus includes the biogenesis, function, and degradation of multiple forms of RNA in eukaryotes. Parker aims to use his research to understand how various diseases and pathologies result from abnormalities in RNA. In 2012, Parker was elected to the National Academy of Sciences in Biochemistry.