The nuclear experience of CPEB: implications for RNA processing and translational control

Cytoplasmic Polyadenylation Element Binding Protein 1 and Atherosclerosis: Prospective Target and New Insights

The ribonucleic acid (RNA)-binding protein Cytoplasmic Polyadenylation Element Binding Protein 1 (CPEB1), a key member of the CPEB family, is essential in controlling gene expression involved in both healthy physiological and pathological processes. CPEB1 can bind to the 3'- untranslated regions (UTR) of substrate messenger ribonucleic acid (mRNA) and regulate its translation. There is increasing evidence that CPEB1 is closely related to the pathological basis of atherosclerosis. According to recent investigations, many pathological processes, including inflammation, lipid metabolism, endothelial dysfunction, angiogenesis, oxidative stress, cellular senescence, apoptosis, and insulin resistance, are regulated by CPEB1. This review considers the prevention and treatment of atherosclerotic heart disease in relation to the evolution of the physiological function of CPEB1, recent research breakthroughs, and the potential participation of CPEB1 in atherosclerosis.

CPEB and translational control by cytoplasmic polyadenylation: impact on synaptic plasticity, learning, and memory

The late 1990s were banner years in molecular neuroscience; seminal studies demonstrated that local protein synthesis, at or near synapses, was necessary for synaptic plasticity, the underlying cellular basis of learning and memory [1, 2]. The newly made proteins were proposed to "tag" the stimulated synapse, distinguishing it from naive synapses, thereby forming a cellular memory [3]. Subsequent studies demonstrated that the transport of mRNAs from soma to dendrite was linked with translational unmasking at synapses upon synaptic stimulation. It soon became apparent that one prevalent mechanism governing these events is cytoplasmic polyadenylation, and that among the proteins that control this process, CPEB, plays a central role in synaptic plasticity, and learning and memory. In vertebrates, CPEB is a family of four proteins, all of which regulate translation in the brain, that have partially overlapping functions, but also have unique characteristics and RNA binding properties that make them control different aspects of higher cognitive function. Biochemical analysis of the vertebrate CPEBs demonstrate them to respond to different signaling pathways whose output leads to specific cellular responses. In addition, the different CPEBs, when their functions go awry, result in pathophysiological phenotypes resembling specific human neurological disorders. In this essay, we review key aspects of the vertebrate CPEB proteins and cytoplasmic polyadenylation within the context of brain function.

Cytoplasmic Polyadenylation Is an Ancestral Hallmark of Early Development in Animals

Differential regulation of gene expression has produced the astonishing diversity of life on Earth. Understanding the origin and evolution of mechanistic innovations for control of gene expression is therefore integral to evolutionary and developmental biology. Cytoplasmic polyadenylation is the biochemical extension of polyadenosine at the 3'-end of cytoplasmic mRNAs. This process regulates the translation of specific maternal transcripts and is mediated by the Cytoplasmic Polyadenylation Element-Binding Protein family (CPEBs). Genes that code for CPEBs are amongst a very few that are present in animals but missing in nonanimal lineages. Whether cytoplasmic polyadenylation is present in non-bilaterian animals (i.e., sponges, ctenophores, placozoans, and cnidarians) remains unknown. We have conducted phylogenetic analyses of CPEBs, and our results show that CPEB1 and CPEB2 subfamilies originated in the animal stem lineage. Our assessment of expression in the sea anemone, Nematostella vectensis (Cnidaria), and the comb jelly, Mnemiopsis leidyi (Ctenophora), demonstrates that maternal expression of CPEB1 and the catalytic subunit of the cytoplasmic polyadenylation machinery (GLD2) is an ancient feature that is conserved across animals. Furthermore, our measurements of poly(A)-tail elongation reveal that key targets of cytoplasmic polyadenylation are shared between vertebrates, cnidarians, and ctenophores, indicating that this mechanism orchestrates a regulatory network that is conserved throughout animal evolution. We postulate that cytoplasmic polyadenylation through CPEBs was a fundamental innovation that contributed to animal evolution from unicellular life.

CPEB1 regulates the inflammatory immune response, phagocytosis, and alternative polyadenylation in microglia

Microglia are myeloid cells of the central nervous system that perform tasks essential for brain development, neural circuit homeostasis, and neural disease. Microglia react to inflammatory stimuli by upregulating inflammatory signaling through several different immune cell receptors such as the Toll-like receptor 4 (TLR4), which signals to several downstream effectors including transforming growth factor beta-activated kinase 1 (TAK1). Here, we show that TAK1 levels are regulated by CPEB1, a sequence-specific RNA binding protein that controls translation as well as RNA splicing and alternative poly(A) site selection in microglia. Lipopolysaccharide (LPS) binds the TLR4 receptor, which in CPEB1-deficient mice leads to elevated expression of ionized calcium binding adaptor molecule 1 (Iba1), a microglial protein that increases with inflammation, and increased levels of the cytokine IL6. This LPS-induced IL6 response is blocked by inhibitors of JNK, p38, ERK, NFκB, and TAK1. In contrast, phagocytosis, which is elevated in CPEB1-deficient microglia, is unaffected by LPS treatment or ERK inhibition, but is blocked by TAK1 inhibition. These data indicate that CPEB1 regulates microglial inflammatory responses and phagocytosis. RNA-seq indicates that these changes in inflammation and phagocytosis are accompanied by changes in RNA levels, splicing, and alternative poly(A) site selection. Thus, CPEB1 regulation of RNA expression plays a role in microglial function.

Localization and Functional Roles of Components of the Translation Apparatus in the Eukaryotic Cell Nucleus

Components of the translation apparatus, including ribosomal proteins, have been found in cell nuclei in various organisms. Components of the translation apparatus are involved in various nuclear processes, particularly those associated with genome integrity control and the nuclear stages of gene expression, such as transcription, mRNA processing, and mRNA export. Components of the translation apparatus control intranuclear trafficking; the nuclear import and export of RNA and proteins; and regulate the activity, stability, and functional recruitment of nuclear proteins. The nuclear translocation of these components is often involved in the cell response to stimulation and stress, in addition to playing critical roles in oncogenesis and viral infection. Many components of the translation apparatus are moonlighting proteins, involved in integral cell stress response and coupling of gene expression subprocesses. Thus, this phenomenon represents a significant interest for both basic and applied molecular biology. Here, we provide an overview of the current data regarding the molecular functions of translation factors and ribosomal proteins in the cell nucleus.

The RNA-binding protein Cpeb4 is a novel positive regulator of osteoclast differentiation

Cytoplasmic polyadenylation element binding (CPEB) proteins are RNA-binding proteins involved in translational regulation of the specific target mRNAs and control function of various organs including brain, liver and hematopoietic system. However, the role of CPEB proteins during osteoclast differentiation remains unclear. Here we show that Cpeb4 is required for RANKL-induced osteoclast differentiation in mouse macrophage-derived RAW264.7 cell line. Cpeb4 mRNA and protein levels are upregulated at the late stage of osteoclast differentiation. Immunofluorescence analysis revealed that Cpeb4 is translocated from cytoplasm to nuclear bodies in response to RANKL stimulation. Inhibition of PI3K-Akt signaling or calcium-NFAT pathways using chemical inhibitors suppressed nuclear localization of Cpeb4. Loss-of-function analysis showed that shRNA-mediated Cpeb4 depletion strongly impaired TRAP-positive osteoclast formation and expression of key differentiation markers including Acp5, Ctsk, Nfatc1 and Dcstamp. These results suggest that Cpeb4 is a positive regulator in osteoclastogenesis downstream of RANKL signaling.

CPEB1 Expression Correlates with Severity of Posttraumatic Ankle Osteoarthritis and Aggravates Catabolic Effect of IL-1β on Chondrocytes

Most cases of posttraumatic ankle osteoarthritis (PTAOA) represent a sequela of ankle fractures. The cytoplasmic polyadenylation element-binding protein 1 (CPEB1) is an RNA binding protein that controls protein expression. Here, we report the previously unappreciated association of CPEB1 with PTAOA. We found that CPEB1 was upregulated in articular cartilage from patients with PTAOA. Additionally, its expression level positively correlated with disease severity. In human primary chondrocytes cultured in vitro, CPEB1 was upregulated when treated with pro-inflammatory cytokines, i.e., IL-1β and TNF-α, suggesting that the observed CPEB1 upregulation in articular cartilage of PTAOA patients may be attributed to local inflammatory milieu. Functionally, CPEB1 overexpression aggravated the catabolic effect of IL-1β on chondrocytes in vitro, and vice versa, its knockdown reduced this effect, together implying a detrimental role of CPEB1 involved in OA progression. In sum, our study identifies CPEB1 as a potential regulator of disease progression of PTAOA.

Is it useful to use several "omics" for obtaining valuable results?

The integration of cell communication and the transfer of signals from stimuli via transcription to translation and further to activation of new protein is crucial for appropriate metabolism and function of living organisms. The overall elucidation and the examination of these complex processes require multistep laboratory approaches in order to obtain results which will not only detect particular stage but also indicate the mechanisms lying upon this process. Such results will be reliable because they will cover multidirectional methods and approaches. The analysis of currently available results already provided with the conclusion that often single omics approach does not correspond with other expected information and may bring misinterpretations. That is why the integration of several "omics" is useful for searching entire explanations and answers as well as appropriate interpretation of obtained complex results. The hypothesis was stated that "from transcriptomics can not be concluded to proteomics". This review focuses on the reasons for the integration of transcriptomic, proteomic and other-omics analysis. Moreover it also describes the examples of clinical meanings and mentions some methods used in these approaches.

CPEB2-dependent translation of long 3'-UTR Ucp1 mRNA promotes thermogenesis in brown adipose tissue

Expression of mitochondrial proton transporter uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) is essential for mammalian thermogenesis. While human UCP1 mRNA exists in a long form only, alternative polyadenylation creates two different isoforms in mice with 10% of UCP1 mRNA found in the long form (Ucp1L) and ~90% in the short form (Ucp1S). We generated a mouse model expressing only Ucp1S and found that it showed impaired thermogenesis due to a 60% drop in UCP1 protein levels, suggesting that Ucp1L is more efficiently translated than Ucp1S. In addition, we found that β3 adrenergic receptor signaling promoted the translation of mouse Ucp1L and human Ucp1 in a manner dependent on cytoplasmic polyadenylation element binding protein 2 (CPEB2). CPEB2-knockout mice showed reduced UCP1 levels and impaired thermogenesis in BAT, which was rescued by ectopic expression of CPEB2. Hence, long 3'-UTR Ucp1 mRNA translation activated by CPEB2 is likely conserved and important in humans to produce UCP1 for thermogenesis.

The translational regulation of maternal mRNAs in time and space

Since their discovery, the study of maternal mRNAs has led to the identification of mechanisms underlying their spatiotemporal regulation within the context of oogenesis and early embryogenesis. Following synthesis in the oocyte, maternal mRNAs are translationally silenced and sequestered into storage in cytoplasmic granules. At the same time, their unique distribution patterns throughout the oocyte and embryo are tightly controlled and connected to their functions in downstream embryonic processes. At certain points in oogenesis and early embryogenesis, maternal mRNAs are translationally activated to perform their functions in a timely manner. The cytoplasmic polyadenylation machinery is responsible for the translational activation of maternal mRNAs, and its role in initiating the maternal to zygotic transition events has recently come to light. Here, we summarize the current knowledge on maternal mRNA regulation, with particular focus on cytoplasmic polyadenylation as a mechanism for translational regulation.

Down-regulation of cancer-associated gene CDC73 contributes to cellular senescence

Dysregulated gene expression is another important contributor in explaining cancer-related phenotypes in addition to mutations. Cellular senescence is a mechanism for the prevention of cancer and thus it is important to understand the regulation of gene expression in senescence due to its potential in anti-cancer therapy. Here, we found that CDC73, which encodes the cell division cycle 73 and acts as a tumor suppressor, was unexpectedly up-regulated in several cancer types but down-regulated in a variety of senescent cells. Importantly, depletion of CDC73 could induce senescence-associated phenotypes in both normal and cancer cells, with an increase in p21 expression. In terms of molecular mechanism, alternative polyadenylation (APA)-mediated 3' untranslated region (3' UTR) lengthening explained, at least in part, the decreased CDC73 expression in senescent cells because longer 3' UTR had a higher rate of RNA degradation compared to the shorter one. Our work discovered that post-transcriptional down-regulation of CDC73 contributed to cellular senescence.

Paxillin and embryonic PolyAdenylation Binding Protein (ePABP) engage to regulate androgen-dependent Xenopus laevis oocyte maturation - A model of kinase-dependent regulation of protein expression

Steroid-triggered Xenopus laevis oocyte maturation is an elegant physiologic model of nongenomic steroid signaling, as it proceeds completely independent of transcription. We previously demonstrated that androgens are the main physiologic stimulator of oocyte maturation in Xenopus oocytes, and that the adaptor protein paxillin plays a crucial role in mediating this process through a positive feedback loop in which paxillin first enhances Mos protein translation, ensued by Erk2 activation and Erk-dependent phosphorylation of paxillin on serine residues. Phosphoserine-paxillin then further augments Mos protein translation and downstream Erk2 activation, resulting in meiotic progression. We hypothesized that paxillin enhances Mos translation by interacting with embryonic PolyAdenylation Binding Protein (ePABP) on polyadenylated Mos mRNA. Knockdown of ePABP phenocopied paxillin knockdown, with reduced Mos protein expression, Erk2 and Cdk1 activation, as well as oocyte maturation. In both Xenopus oocytes and mammalian cells (HEK-293), paxillin and ePABP constitutively interacted. Testosterone (Xenopus) or EGF (HEK-293) augmented ePABP-paxillin binding, as well as ePABP binding to Mos mRNA (Xenopus), in an Erk-dependent fashion. Thus, ePABP and paxillin work together in an Erk-dependent fashion to enhance Mos protein translation and promote oocyte maturation.

Translational Control of Germ Cell Decisions

Germline poses unique challenges to gene expression control at the transcriptional level. While the embryonic germline maintains a global hold on new mRNA transcription, the female adult germline produces transcripts that are not translated into proteins until embryogenesis of subsequent generation. As a consequence, translational control plays a central role in governing various germ cell decisions including the formation of primordial germ cells, self-renewal/differentiation decisions in the adult germline, onset of gametogenesis and oocyte maturation. Mechanistically, several common themes such as asymmetric localization of mRNAs, conserved RNA-binding proteins that control translation by 3' UTR binding, translational activation by the cytoplasmic elongation of the polyA tail and the assembly of mRNA-protein complexes called mRNPs have emerged from the studies on Caenorhabditis elegans, Xenopus and Drosophila. How mRNPs assemble, what influences their dynamics, and how a particular 3' UTR-binding protein turns on the translation of certain mRNAs while turning off other mRNAs at the same time and space are key challenges for future work.

RNA-binding protein CPEB1 remodels host and viral RNA landscapes

Host and virus interactions occurring at the post-transcriptional level are critical for infection but remain poorly understood. Here, we performed comprehensive transcriptome-wide analyses revealing that human cytomegalovirus (HCMV) infection results in widespread alternative splicing (AS), shortening of 3' untranslated regions (3' UTRs) and lengthening of poly(A)-tails in host gene transcripts. We found that the host RNA-binding protein CPEB1 was highly induced after infection, and ectopic expression of CPEB1 in noninfected cells recapitulated infection-related post-transcriptional changes. CPEB1 was also required for poly(A)-tail lengthening of viral RNAs important for productive infection. Strikingly, depletion of CPEB1 reversed infection-related cytopathology and post-transcriptional changes, and decreased productive HCMV titers. Host RNA processing was also altered in herpes simplex virus-2 (HSV-2)-infected cells, thereby indicating that this phenomenon might be a common occurrence during herpesvirus infections. We anticipate that our work may serve as a starting point for therapeutic targeting of host RNA-binding proteins in herpesvirus infections.

New Phosphospecific Antibody Reveals Isoform-Specific Phosphorylation of CPEB3 Protein

Cytoplasmic Polyadenylation Element Binding proteins (CPEBs) are a family of polyadenylation factors interacting with 3’UTRs of mRNA and thereby regulating gene expression. Various functions of CPEBs in development, synaptic plasticity, and cellular senescence have been reported. Four CPEB family members of partially overlapping functions have been described to date, each containing a distinct alternatively spliced region. This region is highly conserved between CPEBs-2-4 and contains a putative phosphorylation consensus, overlapping with the exon seven of CPEB3. We previously found CPEBs-2-4 splice isoforms containing exon seven to be predominantly present in neurons, and the isoform expression pattern to be cell type-specific. Here, focusing on the alternatively spliced region of CPEB3, we determined that putative neuronal isoforms of CPEB3 are phosphorylated. Using a new phosphospecific antibody directed to the phosphorylation consensus we found Protein Kinase A and Calcium/Calmodulin-dependent Protein Kinase II to robustly phosphorylate CPEB3 in vitro and in primary hippocampal neurons. Interestingly, status epilepticus induced by systemic kainate injection in mice led to specific upregulation of the CPEB3 isoforms containing exon seven. Extensive analysis of CPEB3 phosphorylation in vitro revealed two other phosphorylation sites. In addition, we found plethora of potential kinases that might be targeting the alternatively spliced kinase consensus site of CPEB3. As this site is highly conserved between the CPEB family members, we suggest the existence of a splicing-based regulatory mechanism of CPEB function, and describe a robust phosphospecific antibody to study it in future.

CPEB1 mediates epithelial-to-mesenchyme transition and breast cancer metastasis

In mouse mammary epithelial cells, CPEB1 mediates the apical localization of ZO-1 mRNA, which encodes a critical tight junction component. In mice lacking CPEB1 and in cultured cells from which CPEB has been depleted, randomly distributed ZO-1 mRNA leads to the loss of cell polarity. We have investigated whether this diminution of polarity results in an epithelial-to-mesenchyme (EMT) transition and possible increased metastatic potential. Here, we show that CPEB1-depleted mammary epithelial cells alter their gene expression profile in a manner consistent with an EMT and also become motile, which are made particularly robust when cells are treated with TGF-β, an enhancer of EMT. CPEB1-depleted mammary cells become metastatic to the lung following injection into mouse fat pads while ectopically-expressed CPEB1 prevents metastasis. Surprisingly, CPEB1 depletion causes some EMT/metastasis-related mRNAs to have shorter poly(A) tails while other mRNAs to have longer poly(A) tails. Matrix metalloproteinase 9 (MMP9) mRNA, which encodes a metastasis-promoting factor, undergoes poly(A) lengthening and enhanced translation upon CPEB reduction. Moreover, in human breast cancer cells that become progressively more metastatic, CPEB1 is reduced while MMP9 becomes more abundant. These data suggest that at least in part, CPEB1 regulation of MMP9 mRNA expression mediates metastasis of breast cancer cells.

Intranuclear dynamics of the Nup107-160 complex

The Nup107-160 nuclear pore subcomplex (Y-complex) and the chromatin-binding nucleoporin Elys dynamically colocalize with Nup98 and the export factor CRM1 in nuclear GLFG bodies present in HeLa sublines. Thus, in addition to its structural role at the NPC and its mitotic functions, the Y-complex may also act inside the nucleus during interphase.

Nup98 is a glycine-leucine-phenylalanine-glycine (GLFG) repeat–containing nucleoporin that, in addition to nuclear transport, contributes to multiple aspects of gene regulation. Previous studies revealed its dynamic localization within intranuclear structures known as GLFG bodies. Here we show that the mammalian Nup107-160 complex (Y-complex), a major scaffold module of the nuclear pore, together with its partner Elys, colocalizes with Nup98 in GLFG bodies. The frequency and size of GLFG bodies vary among HeLa sublines, and we find that an increased level of Nup98 is associated with the presence of bodies. Recruitment of the Y-complex and Elys into GLFG bodies requires the C-terminal domain of Nup98. During cell division, Y-Nup–containing GLFG bodies are disassembled in mitotic prophase, significantly ahead of nuclear pore disassembly. FRAP studies revealed that, unlike at nuclear pores, the Y-complex shuttles into and out of GLFG bodies. Finally, we show that within the nucleoplasm, a fraction of Nup107, a key component of the Y-complex, displays reduced mobility, suggesting interaction with other nuclear components. Together our data uncover a previously neglected intranuclear pool of the Y-complex that may underscore a yet-uncharacterized function of these nucleoporins inside the nucleus, even in cells that contain no detectable GLFG bodies.

mRNA imprinting: Additional level in the regulation of gene expression

Following its synthesis in the nucleus, mRNA undergoes various stages that are critical for the proper synthesis, localization and possibly functionality of its encoded protein. Recently, we have shown that two RNA polymerase II (Pol II) subunits, Rpb4p and Rpb7p, associate with the nascent transcript co-transcriptionally. This "mRNA imprinting" lasts throughout the mRNA lifetime and is required for proper regulation of all major stages that the mRNA undergoes. Other possible cases of co-transcriptional imprinting are discussed. Since mRNAs can be transported from the synthesizing cell to other cells, we propose that mRNA imprinting can also affect the phenotype of the recipient cells. This can be viewed as "mRNA-based epigenetics."

Arsenite-activated JNK signaling enhances CPEB4-Vinexin interaction to facilitate stress granule assembly and cell survival

Stress granules (SGs) are compartmentalized messenger ribonucleoprotein particles (mRNPs) where translationally repressed mRNAs are stored when cells encounter environmental stress. Cytoplasmic polyadenylation element-binding protein (CPEB)4 is a sequence-specific RNA-binding protein and translational regulator. In keeping with the results obtained from the study of other RNA-binding proteins, we found CPEB4 localized in SGs in various arsenite-treated cells. In this study, we identified that Vinexin, a CPEB4-interacting protein, is a novel component of SGs. Vinexin is a SH3-domain-containing adaptor protein and affects cell migration through its association with Vinculin to localize at focal adhesions (FAs). Unexpectedly, Vinexin is translocated from FAs to SGs under arsenite-induced stress. The recruitment of Vinexin to SGs depends on its interaction with CPEB4 and influences SG formation and cell survival. Arsenite-activated c-Jun N-terminal kinase (JNK) signaling enhances the association between CPEB4 and Vinexin, which consequently facilitates SG localization of Vinexin. Taken together, this study uncovers a novel interaction between a translational regulator and an adaptor protein to influence SG assembly and cell survival.

A fly trap mechanism provides sequence-specific RNA recognition by CPEB proteins

How CPEB RNA-binding proteins regulate cytoplasmic polyadenylation and translation is poorly understood. Allain and colleagues report the structures of the tandem RNA recognition motifs (RRMs) of two human paralogs (CPEB1 and CPEB4) in their free and RNA-bound states. Structural and functional studies reveal how RNA binding by CPEB proteins leads to an optimal positioning of the N-terminal and zinc-binding domains at the 3′ UTR, which favors the nucleation of ribonucleoprotein complexes for translation regulation. This study provides the molecular basis for the translational regulatory circuit established by CPEB proteins.

Cytoplasmic changes in polyA tail length is a key mechanism of translational control and is implicated in germline development, synaptic plasticity, cellular proliferation, senescence, and cancer progression. The presence of a U-rich cytoplasmic polyadenylation element (CPE) in the 3′ untranslated regions (UTRs) of the responding mRNAs gives them the selectivity to be regulated by the CPE-binding (CPEB) family of proteins, which recognizes RNA via the tandem RNA recognition motifs (RRMs). Here we report the solution structures of the tandem RRMs of two human paralogs (CPEB1 and CPEB4) in their free and RNA-bound states. The structures reveal an unprecedented arrangement of RRMs in the free state that undergo an original closure motion upon RNA binding that ensures high fidelity. Structural and functional characterization of the ZZ domain (zinc-binding domain) of CPEB1 suggests a role in both protein–protein and protein–RNA interactions. Together with functional studies, the structures reveal how RNA binding by CPEB proteins leads to an optimal positioning of the N-terminal and ZZ domains at the 3′ UTR, which favors the nucleation of the functional ribonucleoprotein complexes for translation regulation.

Specificity factors in cytoplasmic polyadenylation

Poly(A) tail elongation after export of an messenger RNA (mRNA) to the cytoplasm is called cytoplasmic polyadenylation. It was first discovered in oocytes and embryos, where it has roles in meiosis and development. In recent years, however, has been implicated in many other processes, including synaptic plasticity and mitosis. This review aims to introduce cytoplasmic polyadenylation with an emphasis on the factors and elements mediating this process for different mRNAs and in different animal species. We will discuss the RNA sequence elements mediating cytoplasmic polyadenylation in the 3' untranslated regions of mRNAs, including the CPE, MBE, TCS, eCPE, and C-CPE. In addition to describing the role of general polyadenylation factors, we discuss the specific RNA binding protein families associated with cytoplasmic polyadenylation elements, including CPEB (CPEB1, CPEB2, CPEB3, and CPEB4), Pumilio (PUM2), Musashi (MSI1, MSI2), zygote arrest (ZAR2), ELAV like proteins (ELAVL1, HuR), poly(C) binding proteins (PCBP2, αCP2, hnRNP-E2), and Bicaudal C (BICC1). Some emerging themes in cytoplasmic polyadenylation will be highlighted. To facilitate understanding for those working in different organisms and fields, particularly those who are analyzing high throughput data, HUGO gene nomenclature for the human orthologs is used throughout. Where human orthologs have not been clearly identified, reference is made to protein families identified in man.

Cytoplasmic RNA: a case of the tail wagging the dog

The addition of poly(A) tails to eukaryotic nuclear mRNAs promotes their stability, export to the cytoplasm and translation. Subsequently, the balance between exonucleolytic deadenylation and selective re-establishment of translation-competent poly(A) tails by cytoplasmic poly(A) polymerases is essential for the appropriate regulation of gene expression from oocytes to neurons. In recent years, surprising roles for cytoplasmic poly(A) polymerase-related enzymes that add uridylyl, rather than adenylyl, residues to RNA 3' ends have also emerged. These terminal uridylyl transferases promote the turnover of certain mRNAs but also modify microRNAs, their precursors and other small RNAs to modulate their stability or biological functions.

Ribonucleoprotein complexes that control circadian clocks

Circadian clocks are internal molecular time-keeping mechanisms that enable organisms to adjust their physiology and behavior to the daily surroundings. Misalignment of circadian clocks leads to both physiological and health impairment. Post-transcriptional regulation and translational regulation of circadian clocks have been extensively investigated. In addition, accumulating evidence has shed new light on the involvement of ribonucleoprotein complexes (RNPs) in the post-transcriptional regulation of circadian clocks. Numerous RNA-binding proteins (RBPs) and RNPs have been implicated in the post-transcriptional modification of circadian clock proteins in different model organisms. Herein, we summarize the advances in the current knowledge on the role of RNP complexes in circadian clock regulation.

Translational control of cell growth and malignancy by the CPEBs

The cytoplasmic polyadenylation element binding proteins (CPEBs) associate with specific sequences in mRNA 3' untranslated regions to promote translation. They do so by inducing cytoplasmic polyadenylation, which requires specialized poly(A) polymerases. Aberrant expression of these proteins correlates with certain types of cancer, indicating that cytoplasmic RNA 3' end processing is important in the control of growth. Several CPEB-regulated mRNAs govern cell cycle progression, regulate senescence, establish cell polarity, and promote tumorigenesis and metastasis. In this Opinion article, we discuss the emerging evidence that indicates a key role for the CPEBs in cancer biology.

Poly(A)-specific ribonuclease (PARN): an allosterically regulated, processive and mRNA cap-interacting deadenylase

Deadenylation of eukaryotic mRNA is a mechanism critical for mRNA function by influencing mRNA turnover and efficiency of protein synthesis. Here, we review poly(A)-specific ribonuclease (PARN), which is one of the biochemically best characterized deadenylases. PARN is unique among the currently known eukaryotic poly(A) degrading nucleases, being the only deadenylase that has the capacity to directly interact during poly(A) hydrolysis with both the m(7)G-cap structure and the poly(A) tail of the mRNA. In short, PARN is a divalent metal-ion dependent poly(A)-specific, processive and cap-interacting 3'-5' exoribonuclease that efficiently degrades poly(A) tails of eukaryotic mRNAs. We discuss in detail the mechanisms of its substrate recognition, catalysis, allostery and processive mode of action. On the basis of biochemical and structural evidence, we present and discuss a working model for PARN action. Models of regulation of PARN activity by trans-acting factors are discussed as well as the physiological relevance of PARN.

CPEB1 coordinates alternative 3'-UTR formation with translational regulation

More than half of mammalian genes generate multiple messenger RNA isoforms that differ in their 3' untranslated regions (3' UTRs) and therefore in regulatory sequences, often associated with cell proliferation and cancer; however, the mechanisms coordinating alternative 3'-UTR processing for specific mRNA populations remain poorly defined. Here we report that the cytoplasmic polyadenylation element binding protein 1 (CPEB1), an RNA-binding protein that regulates mRNA translation, also controls alternative 3'-UTR processing. CPEB1 shuttles to the nucleus, where it co-localizes with splicing factors and mediates shortening of hundreds of mRNA 3' UTRs, thereby modulating their translation efficiency in the cytoplasm. CPEB1-mediated 3'-UTR shortening correlates with cell proliferation and tumorigenesis. CPEB1 binding to pre-mRNAs not only directs the use of alternative polyadenylation sites, but also changes alternative splicing by preventing U2AF65 recruitment. Our results reveal a novel function of CPEB1 in mediating alternative 3'-UTR processing, which is coordinated with regulation of mRNA translation, through its dual nuclear and cytoplasmic functions.

CPEB1 regulates the expression of MTDH/AEG-1 and glioblastoma cell migration

Cytoplasmic polyadenylation element-binding protein 1 (CPEB1) is an mRNA-binding protein present in both neurons and glia. CPEB1 is capable of both repressing mRNA translation and activating it depending upon its phosphorylation state. CPEB1-bound mRNAs are held in translational dormancy until CPEB1 is phosphorylated, leading to the cytoplasmic polyadenylation of the bound mRNA that triggers translation. Here, we show that CPEB1 can bind to and regulate translation of the mRNA-encoding metadherin (MTDH, also known as AEG-1 and Lyric) in the rat glioblastoma cell line CNS1. MTDH/AEG-1 is being revealed as a critical signaling molecule in tumor progression, playing roles in invasion, metastasis, and chemoresistance. By using a mutant of CPEB1 that cannot be phosphorylated (thereby holding target mRNAs in translational arrest), we show that inhibiting CPEB1-mediated translation blocks MTDH/AEG-1 expression in vitro and inhibits glioblastomas tumor growth in vivo. CPEB1-mediated translation is likely to impact several signaling pathways that may promote tumor progression, but we present evidence suggesting a role in directed cell migration in glioblastoma cells. In addition, reporter mRNA containing CPEB1-binding sites is transported to the leading edge of migrating cells and translated, whereas the same mRNA with point mutations in the binding sites is synthesized perinuclearly. Our findings show that CPEB1 is hyperactive in rat glioblastoma cells and is regulating an important cohort of mRNAs whose increased translation is fueling the progression of tumor proliferation and dispersal in the brain. Thus, targeting CPEB1-mediated mRNA translation might be a sound therapeutic approach.

MicroRNA-mediated mRNA translation activation in quiescent cells and oocytes involves recruitment of a nuclear microRNP

MicroRNAs can promote translation of specific mRNAs in quiescent (G0) mammalian cells and immature Xenopus laevis oocytes. We report that microRNA-mediated upregulation of target mRNAs in oocytes is dependent on nuclear entry of the microRNA; cytoplasmically-injected microRNA repress target mRNAs. Components of the activation microRNP, AGO, FXR1 (FXR1-iso-a) and miR16 are present in the nucleus and cytoplasm. Importantly, microRNA target mRNAs for upregulation, Myt1, TNFα and a reporter bearing the TNFα AU-rich, microRNA target sequence, are associated with AGO in immature oocyte nuclei and AGO2 in G0 human nuclei, respectively. mRNAs that are repressed or lack target sites are not associated with nuclear AGO. Crosslinking-coupled immunopurification revealed greater association of AGO2 with FXR1 in the nucleus compared to cytoplasm. Consistently, overexpression of FXR1-iso-a rescues activation of cytoplasmically-injected RNAs and in low density, proliferating cells. These data indicate the importance of a compartmentalized AGO2-FXR1-iso-a complex for selective recruitment for microRNA-mediated upregulation.

An unusual two-step control of CPEB destruction by Pin1

Cytoplasmic polyadenylation is a conserved mechanism that controls mRNA translation and stability. A key protein that promotes polyadenylation-induced translation of mRNAs in maturing Xenopus oocytes is the cytoplasmic polyadenylation element binding protein (CPEB). During this meiotic transition, CPEB is subjected to phosphorylation-dependent ubiquitination and partial destruction, which is necessary for successive waves of polyadenylation of distinct mRNAs. Here we identify the peptidyl-prolyl cis-trans isomerase Pin1 as an important factor mediating CPEB destruction. Pin1 interacts with CPEB in an unusual manner in which it occurs prior to CPEB phosphorylation and prior to Pin1 activation by serine 71 dephosphorylation. Upon induction of maturation, CPEB becomes phosphorylated, which occurs simultaneously with Pin1 dephosphorylation. At this time, the CPEB-Pin1 interaction requires cdk1-catalyzed CPEB phosphorylation on S/T-P motifs. Subsequent CPEB ubiquitination and destruction are mediated by a conformational change induced by Pin1 isomerization of CPEB. Similar to M phase progression in maturing Xenopus oocytes, the destruction of CPEB during the mammalian cell cycle requires Pin1 as well. These data identify Pin1 as a new and essential factor regulating CPEB degradation.

The eukaryotic transcriptional machinery regulates mRNA translation and decay in the cytoplasm

In eukaryotes, nuclear mRNA synthesis is physically separated from its cytoplasmic translation and degradation. Recent unexpected findings have revealed that, despite this separation, the transcriptional machinery can remotely control the cytoplasmic stages. Key to this coupling is the capacity of the transcriptional machinery to "imprint" the transcript with factors that escort it to the cytoplasm and regulate its localization, translation and decay. Some of these factors are known transcriptional regulators that also function in mRNA decay and are hence named "synthegradases". Imprinting can be carried out and/or regulated by RNA polymerase II or by promoter cis- and trans-acting elements. This article is part of a Special Issue entitled: RNA polymerase II Transcript Elongation.

The CPEB-family of proteins, translational control in senescence and cancer

Cytoplasmic elongation of the poly(A) tail was originally identified as a mechanism to activate maternal mRNAs, stored as silent transcripts with short poly(A) tails, during meiotic progression. A family of RNA-binding proteins named CPEBs, which recruit the translational repression or cytoplasmic polyadenylation machineries to their target mRNAs, directly mediates cytoplasmic polyadenylation. Recent years have witnessed an explosion of studies showing that CPEBs are not only expressed in a variety of somatic tissues, but have essential functions controlling gene expression in time and space in the adult organism. These "new" functions of the CPEBs include regulating the balance between senescence and proliferation and its pathological manifestation, tumor development. In this review, we summarize current knowledge on the functions of the CPEB-family of proteins in the regulation of cell proliferation, their target mRNAs and the mechanism controlling their activities.

Xtr, a plural tudor domain-containing protein, is involved in the translational regulation of maternal mRNA during oocyte maturation in Xenopus laevis

Xtr in the fertilized eggs of Xenopus has been demonstrated to be a member of a messenger ribonucleoprotein (mRNP) complex that plays a crucial role in karyokinesis during cleavage. Since the Xtr is also present both in oocytes and spermatocytes and its amount increases immediately after spematogenic cells enter into the meiotic phase, this protein was also predicted to act during meiotic progression. Taking advantage of Xenopus oocytes' large size to microinject anti-Xtr antibody into them for inhibition of Xtr function, we examined the role of Xtr in meiotic progression of oocytes. Microinjection of anti-Xtr antibody into immature oocytes followed by reinitiation of oocyte maturation did not affect germinal vesicle break down and the oscillation of Cdc2/cyclin B activity during meiotic progression but caused abnormal spindle formation and chromosomal alignment at meiotic metaphase I and II. Immunoprecipitation of Xtr showed the association of Xtr with FRGY2 and mRNAs such as RCC1 and XL-INCENP mRNAs, which are involved in the progression of karyokinesis. When anti-Xtr antibody was injected into oocytes, translation of XL-INCENP mRNA, which is known to be repressed in immature oocytes and induced after reinitiation of oocyte maturation, was inhibited even if the oocytes were treated with progesterone. A similar translational regulation was observed in oocytes injected with a reporter mRNA, which was composed of an enhanced green fluorescent protein open reading frame followed by the 3' untranslational region (3'UTR) of XL-INCENP mRNA. These results indicate that Xtr regulates the translation of XL-INCENP mRNA through its 3'UTR during meiotic progression of oocyte.

Cytoplasmic RNA-binding proteins and the control of complex brain function

The formation and maintenance of neural circuits in the mammal central nervous system (CNS) require the coordinated expression of genes not just at the transcriptional level, but at the translational level as well. Recent evidence shows that regulated messenger RNA (mRNA) translation is necessary for certain forms of synaptic plasticity, the cellular basis of learning and memory. In addition, regulated translation helps guide axonal growth cones to their targets on other neurons or at the neuromuscular junction. Several neurologic syndromes have been correlated with and indeed may be caused by aberrant translation; one important example is the fragile X mental retardation syndrome. Although translation in the CNS is regulated by multiple mechanisms and factors, we focus this review on regulatory mRNA-binding proteins with particular emphasis on fragile X mental retardation protein (FMRP) and cytoplasmic polyadenylation element binding (CPEB) because they have been shown to be at the nexus of translational control and brain function in health and disease.

NMDAR signaling facilitates the IPO5-mediated nuclear import of CPEB3

Cytoplasmic polyadenylation element-binding protein (CPEB)3 is a nucleocytoplasm-shuttling RNA-binding protein and predominantly resides in the cytoplasm where it represses target RNA translation. When translocated into the nucleus, CPEB3 binds to Stat5b and downregulates Stat5b-dependent transcription. In neurons, the activation of N-methyl-d-aspartate receptors (NMDARs) accumulates CPEB3 in the nucleus and redistributes CPEB3 in the nucleocytoplasmic compartments to control gene expression. Nonetheless, it is unclear which karyopherin drives the nuclear import of CPEB3 and which transport direction is most affected by NMDA stimulation to increase the nuclear pool of CPEB3. Here, we have identified that the karyopherins, IPO5 and CRM1, facilitate CPEB3 translocation by binding to RRM1 and a leucine-containing motif of CPEB3, respectively. NMDAR signaling increases RanBP1 expression and reduces the level of cytoplasmic GTP-bound Ran. These changes enhance CPEB3-IPO5 interaction, which consequently accelerates the nuclear import of CPEB3. This study uncovers a novel NMDA-regulated import pathway to facilitate the nuclear translocation of CPEB3.

Bidirectional control of mRNA translation and synaptic plasticity by the cytoplasmic polyadenylation complex

Translational control of mRNAs in dendrites is essential for certain forms of synaptic plasticity and learning and memory. CPEB is an RNA-binding protein that regulates local translation in dendrites. Here, we identify poly(A) polymerase Gld2, deadenylase PARN, and translation inhibitory factor neuroguidin (Ngd) as components of a dendritic CPEB-associated polyadenylation apparatus. Synaptic stimulation induces phosphorylation of CPEB, PARN expulsion from the ribonucleoprotein complex, and polyadenylation in dendrites. A screen for mRNAs whose polyadenylation is altered by Gld2 depletion identified >100 transcripts including one encoding NR2A, an NMDA receptor subunit. shRNA depletion studies demonstrate that Gld2 promotes and Ngd inhibits dendritic NR2A expression. Finally, shRNA-mediated depletion of Gld2 in vivo attenuates protein synthesis-dependent long-term potentiation (LTP) at hippocampal dentate gyrus synapses; conversely, Ngd depletion enhances LTP. These results identify a pivotal role for polyadenylation and the opposing effects of Gld2 and Ngd in hippocampal synaptic plasticity.

CPEB-mediated ZO-1 mRNA localization is required for epithelial tight-junction assembly and cell polarity

CPEB is a translational regulatory sequence-specific RNA-binding protein that controls germ cell development. Here we show that CPEB heterozygous female mice are fertile but contain disorganized mammary epithelial cells, in which zonal occludens-1 and claudin-3, apical tight-junction proteins, are mislocalized. CPEB depletion from mammary epithelial cells disrupts zonal occludens-1 apical localization and tight-junction distribution; conversely, ectopic expression of CPEB enhances zonal occludens-1 localization. CPEB and zonal occludens-1 mRNA are co-localized apically and zonal occludens-1 3' untranslated region-binding sites for CPEB are necessary for RNA localization. In a three-dimensional culture system that models lumen-containing mammary ducts, depletion of CPEB or zonal occludens-1 impairs central cavity formation, indicating a loss of cell polarity. Cavity formation in zonal occludens-1-depleted cells is rescued when they are transduced with zonal occludens-1 mRNA containing, but not lacking, CPEB-binding sites. Our data demonstrate that CPEB-mediated zonal occludens-1 mRNA localization is essential for tight-junction assembly and mammary epithelial cell polarity.

RNA-related nuclear functions of human Pat1b, the P-body mRNA decay factor

The evolutionarily conserved Pat1 proteins are P-body components recently shown to play important roles in cytoplasmic gene expression control. Using human cell lines, we demonstrate that human Pat1b is a shuttling protein whose nuclear export is mediated via a consensus NES sequence and Crm1, as evidenced by leptomycin B (LMB) treatment. However, not all P-body components are nucleocytoplasmic proteins; rck/p54, Dcp1a, Edc3, Ge-1, and Xrn1 are insensitive to LMB and remain cytoplasmic in its presence. Nuclear Pat1b localizes to PML-associated foci and SC35-containing splicing speckles in a transcription-dependent manner, whereas in the absence of RNA synthesis, Pat1b redistributes to crescent-shaped nucleolar caps. Furthermore, inhibition of splicing by spliceostatin A leads to the reorganization of SC35 speckles, which is closely mirrored by Pat1b, indicating that it may also be involved in splicing processes. Of interest, Pat1b retention in these three nuclear compartments is mediated via distinct regions of the protein. Examination of the nuclear distribution of 4E-T(ransporter), an additional P-body nucleocytoplasmic protein, revealed that 4E-T colocalizes with Pat1b in PML-associated foci but not in nucleolar caps. Taken together, our findings strongly suggest that Pat1b participates in several RNA-related nuclear processes in addition to its multiple regulatory roles in the cytoplasm.

CPEB2-eEF2 interaction impedes HIF-1α RNA translation

Translation of mRNA into protein proceeds in three phases: initiation, elongation, and termination. Regulated translation allows the prompt production of selective proteins in response to physiological needs and is often controlled by sequence-specific RNA-binding proteins that function at initiation. Whether the elongation phase of translation can be modulated individually by trans-acting factors to synthesize polypeptides at variable rates remains to be determined. Here, we demonstrate that the RNA-binding protein, cytoplasmic polyadenylation element binding protein (CPEB)2, interacts with the elongation factor, eEF2, to reduce eEF2/ribosome-triggered GTP hydrolysis in vitro and slow down peptide elongation of CPEB2-bound RNA in vivo. The interaction of CPEB2 with eEF2 downregulates HIF-1α RNA translation under normoxic conditions; however, when cells encounter oxidative stress, CPEB2 dissociates from HIF-1α RNA, leading to rapid synthesis of HIF-1α for hypoxic adaptation. This study delineates the molecular mechanism of CPEB2-repressed translation and presents a unique model for controlling transcript-selective translation at elongation.

Characterization of RNase MRP RNA and novel snoRNAs from Giardia intestinalis and Trichomonas vaginalis

Background

Eukaryotic cells possess a complex network of RNA machineries which function in RNA-processing and cellular regulation which includes transcription, translation, silencing, editing and epigenetic control. Studies of model organisms have shown that many ncRNAs of the RNA-infrastructure are highly conserved, but little is known from non-model protists. In this study we have conducted a genome-scale survey of medium-length ncRNAs from the protozoan parasites Giardia intestinalis and Trichomonas vaginalis.

Results

We have identified the previously 'missing' Giardia RNase MRP RNA, which is a key ribozyme involved in pre-rRNA processing. We have also uncovered 18 new H/ACA box snoRNAs, expanding our knowledge of the H/ACA family of snoRNAs.

Conclusions

Results indicate that Giardia intestinalis and Trichomonas vaginalis, like their distant multicellular relatives, contain a rich infrastructure of RNA-based processing. From here we can investigate the evolution of RNA processing networks in eukaryotes.

Machine vision-based localization of nucleic and cytoplasmic injection sites on low-contrast adherent cells

Automated robotic bio-micromanipulation can improve the throughput and efficiency of single-cell experiments. Adherent cells, such as fibroblasts, include a wide range of mammalian cells and are usually very thin with highly irregular morphologies. Automated micromanipulation of these cells is a beneficial yet challenging task, where the machine vision sub-task is addressed in this article. The necessary but neglected problem of localizing injection sites on the nucleus and the cytoplasm is defined and a novel two-stage model-based algorithm is proposed. In Stage I, the gradient information associated with the nucleic regions is extracted and used in a mathematical morphology clustering framework to roughly localize the nucleus. Next, this preliminary segmentation information is used to estimate an ellipsoidal model for the nucleic region, which is then used as an attention window in a k-means clustering-based iterative search algorithm for fine localization of the nucleus and nucleic injection site (NIS). In Stage II, a geometrical model is built on each localized nucleus and employed in a new texture-based region-growing technique called Growing Circles Algorithm to localize the cytoplasmic injection site (CIS). The proposed algorithm has been tested on 405 images containing more than 1,000 NIH/3T3 fibroblast cells, and yielded the precision rates of 0.918, 0.943, and 0.866 for the NIS, CIS, and combined NIS-CIS localizations, respectively.

Translational control in oocyte development

Translational control of specific mRNAs is a widespread mechanism of gene regulation, and it is especially important in pattern formation in the oocytes of organisms in which the embryonic axes are established maternally. Drosophila and Xenopus have been especially valuable in elucidating the relevant molecular mechanisms. Here, we comprehensively review what is known about translational control in these two systems, focusing on examples that illustrate key concepts that have emerged. We focus on protein-mediated translational control, rather than regulation mediated by small RNAs, as the former appears to be predominant in controlling these developmental events. Mechanisms that modulate the ability of the specific mRNAs to be recruited to the ribosome, that regulate polyadenylation of specific mRNAs, or that control the association of particular mRNAs into translationally inert ribonucleoprotein complexes will all be discussed.

Insights into 4E-BP1 and p53 mediated regulation of accelerated cell senescence

Senescence is a valid tumor suppressive mechanism in cancer. Accelerated cell senescence describes the growth arrested state of cells that have been treated with anti-tumor drugs, such as doxorubicin that induce a DNA damage response. Discodermolide, a microtubule-stabilizing agent, is a potent inducer of accelerated cell senescence. Resistance to discodermolide is mediated via resistance to accelerated cell senescence, and is associated with reduced expression of the mTORC1 substrate, 4E-BP1 and increased expression of p53 [1]. Although the association of p53 with senescence induction is well-characterized, senescence reversion in the presence of high expression of p53 has not been well-documented. Furthermore, studies addressing the role of mTOR signaling in regulating senescence have been limited and recent data implicate a novel, senescence-associated role for 4E-BP1 in crosstalk with the transcription factor p53. This research perspective will address these somewhat contradictory findings and summarize recent research regarding senescence and mTORC1 signaling.

CPEB4 is a cell survival protein retained in the nucleus upon ischemia or endoplasmic reticulum calcium depletion

The RNA binding protein CPEB (cytoplasmic polyadenylation element binding) regulates cytoplasmic polyadenylation and translation in germ cells and the brain. In neurons, CPEB is detected at postsynaptic sites, as well as in the cell body. The related CPEB3 protein also regulates translation in neurons, albeit probably not through polyadenylation; it, as well as CPEB4, is present in dendrites and the cell body. Here, we show that treatment of neurons with ionotropic glutamate receptor agonists causes CPEB4 to accumulate in the nucleus. All CPEB proteins are nucleus-cytoplasm shuttling proteins that are retained in the nucleus in response to calcium-mediated signaling and alpha-calcium/calmodulin-dependent kinase protein II (CaMKII) activity. CPEB2, -3, and -4 have conserved nuclear export signals that are not present in CPEB. CPEB4 is necessary for cell survival and becomes nuclear in response to focal ischemia in vivo and when cultured neurons are deprived of oxygen and glucose. Further analysis indicates that nuclear accumulation of CPEB4 is controlled by the depletion of calcium from the ER, specifically, through the inositol-1,4,5-triphosphate (IP3) receptor, indicating a communication between these organelles in redistributing proteins between subcellular compartments.

Sequence analysis and genetic variability of stearoyl CoA desaturase (SCD) gene in the Italian Mediterranean river buffalo

Stearoyl-CoA desaturase (SCD) plays a key metabolic role by changing the saturated FA content of ruminant milk and meat. In this study we characterized for the first time the stearoyl-CoA desaturase (SCD) gene in river buffalo (Bubalus bubalis) and investigated its genetic variability. On a total of 78 buffaloes, 15 SNPs were detected and 6 of them were preliminarily genotyped. In particular, the g.133A>C SNP was found to create a new consensus site for the SP1 binding site, thus generating a new tandem repeat in the promoter region. A preliminary association study with the milk fatty acid content showed that the C allele significantly affects the total desaturation index (P<0.01). Linkage disequilibrium analysis allowed identification of 7 haplotypes and 4 tag SNPs. Such polymorphisms could represent useful genetic markers for association studies with fatty acid composition, but further studies are needed to evaluate their potential use to improve the nutritional quality of the dairy products.

KHDC1B is a novel CPEB binding partner specifically expressed in mouse oocytes and early embryos

mRNAs required for meiotic maturation and early embryonic development are stored in growing oocytes. These transcripts are translationally repressed until hormonal cues trigger ovulation. Errors in translation underlie some cases of human infertility and are associated with ovarian germ cell tumors. However, it remains unclear how maternal transcripts are kept quiescent in mammals. This study describes a potential translational regulator, KHDC1B. KHDC1B is a member of a small family of KH-domain containing proteins specific to eutherian mammals. Two family members, KHDC1A and 1B, are highly expressed in oocytes. KHDC1A and 1B bind polyU agarose and form oligomers like other KH-domain proteins. The functions of these proteins were tested by expression in Xenopus embryos. KHDC1A caused cell death, whereas KHDC1B caused cleavage arrest. This arrest phenotype was rescued by coexpression of the mouse translational regulator cytoplasmic polyadenylation binding protein 1 (mCPEB1). Coimmunoprecipitation and coimmunostaining experiments confirmed the functional interaction between KHDC1B and mCPEB1. Finally, KHDC1B levels and binding partners were shown to fluctuate with the cell cycle. KHDC1B, via its interaction with mCEPB1, may regulate translation of mRNA targets required for oocyte maturation.

A novel role of CPEB3 in regulating EGFR gene transcription via association with Stat5b in neurons

CPEB3 is a sequence-specific RNA-binding protein and represses translation of its target mRNAs in neurons. Here, we have identified a novel function of CPEB3 as to interact with Stat5b and inhibit its transcription activity in the nucleus without disrupting dimerization, DNA binding and nuclear localization of Stat5b. Moreover, CPEB3 is a nucleocytoplasm-shuttling protein with predominant residence in the cytoplasm; whereas activation of NMDA receptors accumulates CPEB3 in the nucleus. Using the knockdown approach, we have found the receptor tyrosine kinase, EGFR, is a target gene transcriptionally activated by Stat5b and downregulated by CPEB3 in neurons. The increased EGFR expression in CPEB3 knockdown neurons, when stimulated with EGF, alters the kinetics of downstream signaling. Taken together, CPEB3 has a novel function in the nucleus as to suppress Stat5b-dependent EGFR gene transcription. Consequently, EGFR signaling is negatively regulated by CPEB3 in neurons.