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Comment |
mRNA spindle localization and mitotic translational regulation by CPEB1 and CPEB4. Pascual R et al. (2020) Transition through cell cycle phases requires temporal and spatial regulation of gene expression to ensure accurate chromosome duplication and segregation. This regulation involves dynamic reprogramming of gene expression at multiple transcriptional and posttranscriptional levels. In transcriptionally silent oocytes, the CPEB-family of RNAbinding proteins coordinates temporal and spatial translation regulation of stored maternal mRNAs to drive meiotic progression. CPEB1 mediates mRNA localization to the meiotic spindle, which is required to ensure proper chromosome segregation. Temporal translational regulation also takes place in mitosis, where a large repertoire of transcripts are activated or repressed in specific cell cycle phases. However, whether control of localized translation at the spindle is required for mitosis is unclear, as mitotic and acentriolar-meiotic spindles are functionally and structurally different. Furthermore, the large differences in scale-ratio between cell volume and spindle size in oocytes compared to somatic mitotic cells may generate distinct requirements for gene expression compartmentalization in meiosis and mitosis. Here we show that mitotic spindles contain CPE-localized mRNAs and translating ribosomes. Moreover, CPEB1 and CPEB4 localize in the spindles and they may function sequentially in promoting mitotic stage transitions and correct chromosome segregation. Thus, CPEB1 and CPEB4 bind to specific spindle-associated transcripts controlling the expression and/or localization of their encoded factors that, respectively, drive metaphase and anaphase/cytokinesis.//////////////////
MAPK cascade couples maternal mRNA translation and degradation to meiotic cell cycle progression in mouse oocyte. Sha QQ et al. (2016) Mammalian oocyte maturation depends on the translational activation of stored maternal mRNAs upon meiotic resumption. Cytoplasmic polyadenylation element binding protein-1 (CPEB1) is a key oocyte factor that regulates maternal mRNA translation. However, the signal that triggers CPEB1 activation at the onset of mammalian oocyte maturation is not known. We provide evidence that a mitogen-activated protein kinase (MAPK) cascade couples maternal mRNA translation to meiotic cell cycle progression in mouse oocytes, by triggering CPEB1 phosphorylation and degradation. Mutations of the phosphorylation sites or ubiquitin E3 ligase binding sites in CPEB1 have a dominant negative effect in oocytes, and mimic the phenotype of ERK1/2 knockout, by impairing spindle assembly and mRNA translation. Overexpression of the CPEB1-downstream translation activator DAZL in ERK1/2-deficient oocytes partially rescued the meiotic defects, indicating that ERK1/2 is essential for spindle assembly, metaphase II arrest, and maternal-zygotic transition (MZT) primarily by triggering the translation of key maternal mRNAs. Taken together, ERK1/2-mediated CPEB1 phosphorylation/degradation is a major mechanism of maternal mRNA translational activation, and is crucial for mouse oocyte maturation and MZT.//////////////////
DAZL and CPEB1 regulate mRNA translation synergistically during oocyte maturation. Martins JP et al. (2016) Meiotic progression requires exquisitely coordinated translation of maternal mRNA accumulated during oocyte growth. A major regulator of this program is the cytoplasmic polyadenylation element binding protein 1 (CPEB1). However, the temporal pattern of translation at different meiotic stages implies the function of additional RNA binding proteins (RBPs). Here we report that deleted in azoospermia-like (DAZL) cooperates with CPEB1 to regulate maternal mRNA translation. Using a strategy that monitors ribosome loading onto endogenous mRNAs and a prototypic translation target, we show that ribosome loading is induced in a DAZL- and CPEB1-dependent manner, as the oocyte reenters meiosis. Depletion of the two RBPs from oocytes and 3' UTR mutagenesis demonstrate that both RBPs interact with Tex19.1 3' UTR and cooperate in translation activation of this mRNA. We observed a synergism between DAZL and cytoplasmic polyadenylation elements (CPE) in the translation pattern of maternal mRNAs when using a genome-wide analysis. Mechanistically, the number of DAZL proteins loaded on to the mRNA and the characteristics of the CPE may define the degree of cooperation between the two RBPs in activating translation and meiotic progression.//////////////////
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Comment |
Genome-wide analysis of translation reveals a critical role for deleted in azoospermia-like (Dazl) at the oocyte-to-zygote transition. Chen J et al. Oocyte maturation, fertilization, and early embryonic development occur in the absence of gene transcription. Therefore, it is critical to understand at a global level the post-transcriptional events that are driving these transitions. Here we used a systems approach by combining polysome mRNA profiling and bioinformatics to identify RNA-binding motifs in mRNAs that either enter or exit the polysome pool during mouse oocyte maturation. Association of mRNA with the polysomes correlates with active translation. Using this strategy, we identified highly specific patterns of mRNA recruitment to the polysomes that are synchronized with the cell cycle. A large number of the mRNAs recovered with translating ribosomes contain motifs for the RNA-binding proteins DAZL (deleted in azoospermia-like) and CPEB (cytoplasmic polyadenylation element-binding protein). Although a Dazl role in early germ cell development is well established, no function has been described during oocyte-to-embryo transition. We demonstrate that CPEB1 regulates Dazl post-transcriptionally, and that DAZL is essential for meiotic maturation and embryonic cleavage. In the absence of DAZL synthesis, the meiotic spindle fails to form due to disorganization of meiotic microtubules. Therefore, Cpeb1 and Dazl function in a progressive, self-reinforcing pathway to promote oocyte maturation and early embryonic development.
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Mutations |
4 mutations
Species: mouse
Mutation name: None
type: null mutation
fertility: infertile - ovarian defect
Comment: Germ cell differentiation and synaptonemal complex formation are disrupted in CPEB knockout mice. Tay J et al. CPEB is a sequence-specific RNA binding protein that regulates translation during vertebrate oocyte maturation. Adult female CPEB knockout mice contained vestigial ovaries that were devoid of oocytes; ovaries from mid-gestation embryos contained oocytes that were arrested at the pachytene stage. Male CPEB null mice also contained germ cells arrested at pachytene. The germ cells from the knockout mice harbored fragmented chromatin, suggesting a possible defect in homologous chromosome adhesion or synapsis. Two CPE-containing synaptonemal complex protein mRNAs, which interact with CPEB in vitro and in vivo, contained shortened poly(A) tails and mostly failed to sediment with polysomes in the null mice. Synaptonemal complexes were not detected in these animals. CPEB therefore controls germ cell differentiation by regulating the formation of the synaptonemal complex.
Species: human
Mutation name:
type: naturally occurring
fertility: subfertile
Comment: Deletion of CPEB1 gene: a rare but recurrent cause of premature ovarian insufficiency (POI). Hyon C et al. (2016) Premature ovarian insufficiency (POI) may be secondary to chemotherapy, radiotherapy or environmental factors. Genetic causes are identified in 20-25% of cases, but most POI cases remain idiopathic. To identify new genes involved in POI and to characterize the implication of CPEB1 gene in POI. Case report and cohort study replicate Setting: Study conducted in academic medical centers. A deletion including CPEB1vgene was first identified in a patient with primary amenorrhea. Secondly, 191 sporadic POI cases and 68 familial POI cases were included. For each patient, karyotype was normal and FMR1 premutation was excluded. Search for CPEB1 deletions was performed by Quantitative Multiplex PCR of Short Fluorescent Fragments (QMPSF) or DNA microarray analysis. Gene sequencing of CPEB1 was done for 95 patients. We identified 3 patients carrying a microdeletion in band 15q25.2. The proximal breakpoint, for the three patients, falls within a low copy repeat (LCR) region disrupting the CPEB1 gene which represents a strong candidate gene for POI as it is known to be implicated in oocyte meiosis. No mutation was identified by sequencing CPEB1 gene. Therefore heterozygous deletion of CPEB1 gene leading to haploinsufficiency, could be responsible for POI in humans. Microdeletions of CPEB1 were identified in 1.3% of patients with POI, whereas no mutation was identified. This microdeletion is rare but recurrent as it is mediated by NAHR due to the existence of LCRs in the region. This result demonstrates the importance of DNA microarray analysis in etiological evaluation and counseling of patients with POI.//////////////////
Species: human
Mutation name:
type: naturally occurring
fertility: subfertile
Comment: High-resolution array-CGH analysis on 46,XX patients affected by early onset primary ovarian insufficiency discloses new genes involved in ovarian function. Bestetti I et al. (2019) Can high resolution array-CGH analysis on a cohort of women showing a primary ovarian insufficiency (POI) phenotype in young age identify copy number variants (CNVs) with a deleterious effect on ovarian function? This approach has proved effective to clarify the role of CNVs in POI pathogenesis and to better unveil both novel candidate genes and pathogenic mechanisms. POI describes the progression toward the cessation of ovarian function before the age of 40 years. Genetic causes are highly heterogeneous and despite several genes being associated with ovarian failure, most of genetic basis of POI still needs to be elucidated. The current study included 67 46,XX patients with early onset POI (<19 years) and 134 control females recruited between 2012 and 2016 at the Medical Cytogenetics and Molecular Genetics Lab, IRCCS Istituto Auxologico Italiano. High resolution array-CGH analysis was carried out on POI patients' DNA. Results of patients and female controls were analyzed to search for rare CNVs. All variants were validated and subjected to a gene content analysis and disease gene prioritization based on the present literature to find out new ovary candidate genes. Case-control study with statistical analysis was carried out to validate our approach and evaluate any ovary CNVs/gene enrichment. Characterization of particular CNVs with molecular and functional studies was performed to assess their pathogenic involvement in POI. We identified 37 ovary-related CNVs involving 44 genes with a role in ovary in 32 patients. All except one of the selected CNVs were not observed in the control group. Possible involvement of the CNVs in POI pathogenesis was further corroborated by a case-control analysis that showed a significant enrichment of ovary-related CNVs/genes in patients (P = 0.0132; P = 0.0126). Disease gene prioritization identified both previously reported POI genes (e.g. BMP15, DIAPH2, CPEB1, BNC1) and new candidates supported by transcript and functional studies, such as TP63 with a role in oocyte genomic integrity and VLDLR which is involved in steroidogenesis. ClinVar database (http://www.ncbi.nlm.nih.gov/clinvar/); accession numbers SCV000787656 to SCV000787743. This is a descriptive analysis for almost all of the CNVs identified. Inheritance studies of CNVs in some non-familial sporadic cases was not performed as the parents' DNA samples were not available. Addionally, RT-qPCR analyses were carried out in few cases as RNA samples were not always available and the genes were not expressed in blood. Our array-CGH screening turned out to be efficient in identifying different CNVs possibly implicated in disease onset, thus supporting the extremely wide genetic heterogeneity of POI. Since almost 50% of cases are negative rare ovary-related CNVs, array-CGH together with next generation sequencing might represent the most suitable approach to obtain a comprehensive genetic characterization of POI patients. Supported by Italian Ministry of Health grants 'Ricerca Corrente' (08C203_2012) and 'Ricerca Finalizzata' (GR-2011-02351636, BIOEFFECT) to IRCCS Istituto Auxologico Italiano.//////////////////
Species: human
Mutation name:
type: naturally occurring
fertility: fertile
Comment: CPEB1 deletion is not a common explanation for premature ovarian insufficiency in a Chinese cohort. Jiao W et al. (2020) Premature ovarian insufficiency (POI), which is characterized by early menopause before the age of 40 years, affects approximately 1-5% of women. Cytoplasmic polyadenylation element binding protein 1 (CPEB1) is a post-transcriptional regulatory protein that is highly expressed in germ cells and promotes oocytes maturation, and several studies have found microdeletions of chromosome 15q25.2, which contains the CPEB1 gene, in POI patients. However, the deleted region also includes other plausible genes, and thus the contribution of CPEB1 to POI is uncertain. The present study aimed to determine the relationship between CPEB1 deletion and POI in a Chinese cohort. Quantitative real-time polymerase chain reaction (qPCR) with primers for exon 4 and exon 11 of CPEB1 was performed to detect the CPEB1 deletion in 323 patients with POI and in 300 healthy controls. Subsequent qPCR with primers for each exon of CPEB1 was performed to precisely localize the deletion locus. One patient with primary amenorrhea was found to carry a heterozygous deletion of exons 8-12 of the CPEB1 gene. Our study is the first to search for CPEB1 deletions in POI patients using a simple qPCR method, and we show that CPEB1 deletion is not a common cause for POI in a Chinese cohort.//////////////////
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