Poly(A)-binding proteins are required for translational regulation in vertebrate oocytes and early embryos. Ozturk S et al. (2017) Poly(A)-binding proteins (PABPs) function in the timely regulation of gene expression during oocyte maturation, fertilisation and early embryo development in vertebrates. To this end, PABPs bind to poly(A) tails or specific sequences of maternally stored mRNAs to protect them from degradation and to promote their translational activities. To date, two structurally different PABP groups have been identified: (1) cytoplasmic PABPs, including poly(A)-binding protein, cytoplasmic 1 (PABPC1), embryonic poly(A)-binding protein (EPAB), induced PABP and poly(A)-binding protein, cytoplasmic 3; and (2) nuclear PABPs, namely embryonic poly(A)-binding protein 2 and nuclear poly(A)-binding protein 1. Many studies have been undertaken to characterise the spatial and temporal expression patterns and subcellular localisations of PABPC1 and EPAB in vertebrate oocytes and early embryos. In the present review, we comprehensively evaluate and discuss the expression patterns and particular functions of the EPAB and PABPC1 genes, especially in mouse and human oocytes and early embryos.//////////////////
Embryonic poly(A)-binding protein (EPAB) is required for granulosa cell EGF signaling and cumulus expansion in female mice. Yang CR et al. (2015) Embryonic poly (A)-binding protein (EPAB) is the predominant poly(A)-binding protein in Xenopus, mouse, and human oocytes and early embryos prior to zygotic genome activation (ZGA). EPAB is required for translational activation of maternally-stored mRNAs in the oocyte and Epab(-/-) female mice are infertile due to impaired oocyte maturation, cumulus expansion, and ovulation. The aim of this study was to characterize the mechanism of follicular somatic cell dysfunction in Epab(-/-) mice. Using a co-culture system of oocytectomized cumulus oophorus complexes (OOXs) with denuded oocytes, we found that when WT OOXs were co-cultured with Epab(-/-) oocytes, or when Epab(-/-) OOXs were co-cultured with WT oocytes, cumulus expansion failed to occur in response to epidermal growth factor (EGF). This finding suggests that oocytes and cumulus cells (CCs) from Epab(-/-) mice fail to send and receive the necessary signals required for cumulus expansion. The abnormalities in Epab(-/-) CCs are not due to lower expression of the oocyte-derived factors growth differentiation factor 9 (GDF9) or bone morphogenic protein 15 (BMP15) since Epab(-/-) oocytes express these proteins at comparable levels to WT. Epab(-/-) granulosa cells (GCs) exhibit decreased levels of p-MEK1/2, p-ERK1/2, and p-p90RSK in response to LH and EGF treatment, as well as decreased phosphorylation of the EGF receptor (p-EGFR). In conclusion, EPAB, which is oocyte-specific, is required for the ability of CCs and GCs to become responsive to LH and EGF signaling. These results emphasize the importance of oocyte-somatic communication for GC and CC function.//////////////////
Embryonic Poly(A) Binding Protein (EPAB) Is Required During Early Stages of Mouse Oocyte Development for Chromatin Organization, Transcriptional Silencing, and Meiotic Competence. Lowther KM et al. (2015) During oocyte maturation, fertilization, and early embryo development until zygotic genome activation (ZGA), transcription is suppressed and gene expression is dependent upon the timely activation of stored mRNAs. Embryonic poly(A) binding protein (EPAB) is the predominant poly(A)-binding protein in Xenopus, mouse, and human oocytes and early embryos, and is important for regulating translational activation of maternally-stored mRNAs. EPAB is critical for early development since Epab(-/-) female mice do not produce mature eggs and are infertile. In this study, we further characterize morphological and molecular aspects of Epab(-/-) oocytes. We demonstrate that Epab(-/-) oocytes are smaller in size, contain peripheral GVs, and are loosely associated with cumulus cells. Chromatin reorganization to the surrounded nucleolus (SN) configuration and transcriptional silencing that normally occurs during oocyte growth does not occur in Epab(-/-) oocytes. Interestingly, microinjection of Epab mRNA into Epab(-/-) preantral follicle-enclosed oocytes rescues reorganization of chromatin and oocyte maturation to metaphase II. Overall, these results demonstrate an important role for EPAB during oocyte growth and the acquisition of meiotic competence.//////////////////An embryonic poly(A)-binding protein (ePAB) is expressed in mouse oocytes and early preimplantation embryos. Seli E et al. (2005) Gene expression during oocyte maturation, fertilization, and early embryo development until zygotic gene activation is regulated mainly by translational activation of maternally derived mRNAs. This process requires the presence of a poly(A)-binding protein. However, the cytoplasmic somatic cell poly(A)-binding protein (PABP1) is not expressed until later in embryogenesis. We recently identified an embryonic poly(A)-binding protein (ePAB) in Xenopus. ePAB is the predominant cytoplasmic PABP in Xenopus oocytes and early embryos and prevents deadenylation of mRNAs, suggesting its importance in the regulation of gene expression during early Xenopus development. Here we report the identification of the mouse ortholog of Xenopus ePAB. The mouse ePAB gene on chromosome 2 contains 14 exons that specify an alternatively spliced mRNA encoding a protein of 608 or 561 aa with approximately 65% identity to Xenopus ePAB. Mouse ePAB mRNA is expressed in ovaries and testis but not in somatic tissues. In situ hybridization localizes ePAB RNA to oocytes and confirms its absence from surrounding somatic cells in the mouse ovary. During early development, mouse ePAB is expressed in prophase I and metaphase II oocytes and one-cell and two-cell embryos and then becomes undetectable in four-or-more-cell embryos. In contrast, PABP1 mRNA expression is minimal in oocytes and early embryos until the eight-cell stage when it increases, becoming predominant at the blastocyst stage. The expression of mouse ePAB before zygotic gene activation argues for its importance in translational activation of maternally derived mRNAs during mammalian oocyte and early preimplantation embryo development./////////////////Superovulation alters embryonic poly(A)-binding protein (Epab) and poly(A)-binding protein, cytoplasmic 1 (Pabpc1) gene expression in mouse oocytes and early embryos. Ozturk S et al. (2014) Embryonic poly(A)-binding protein (EPAB) and poly(A)-binding protein, cytoplasmic 1 (PABPC1) play critical roles in translational regulation of stored maternal mRNAs required for proper oocyte maturation and early embryo development in mammals. Superovulation is a commonly used technique to obtain a great number of oocytes in the same developmental stages in assisted reproductive technology (ART) and in clinical or experimental animal studies. Previous studies have convincingly indicated that superovulation alone can cause impaired oocyte maturation, delayed embryo development, decreased implantation rate and increased postimplantation loss. Although how superovulation results in these disturbances has not been clearly addressed yet, putative changes in genes related to oocyte and early embryo development seem to be potential risk factors. Thus, the aim of the present study was to determine the effect of superovulation on Epab and Pabpc1 gene expression. To this end, low- (5IU) and high-dose (10IU) pregnant mare's serum gonadotropin (PMSG) and human chorionic gonadotrophin (hCG) were administered to female mice to induce superovulation, with naturally cycling female mice serving as controls. Epab and Pabpc1 gene expression in germinal vesicle (GV) stage oocytes, MII oocytes and 1- and 2-cell embryos collected from each group were quantified using quantitative reverse transcription-polymerase chain reaction. Superovulation with low or high doses of gonadotropins significantly altered Epab and Pabpc1 mRNA levels in GV oocytes, MII oocytes and 1- and 2-cell embryos compared with their respective controls (P<0.05). These changes most likely lead to variations in expression of EPAB- and PABPC1-regulated genes, which may adversely influence the quality of oocytes and early embryos retrieved using superovulation.//////////////////
Expression regulated by
Comment
Ovarian localization
Oocyte, Granulosa
Comment
Epab and Pabpc1 are differentially expressed in the postnatal mouse ovaries. Ozturk S et al. (2015) Embryonic poly(A)-binding protein (EPAB) and poly(A)-binding protein, cytoplasmic 1 (PABPC1) bind poly(A) tails of mRNAs and mediate their translational regulation in germ cells and early preimplantation embryos. Although expression patterns and possible functions of the Epab and Pabpc1 genes have been examined in vertebrate germ cells and early embryos, their expression levels and cellular localizations in the postnatal mouse ovaries remained elusive. In the present study, we first aimed to characterize expression levels of the Epab and Pabpc1 genes in the prepubertal (1-, 2-, and 3-week old), pubertal (4-, 5-, and 6-week old), postpubertal (16-week and 18-week old), and aged (52-, 60-, and 72-week old) mouse ovaries by using quantitative real-time polymerase chain reaction (qRT-PCR). Epab mRNA was predominantly expressed in the prepubertal ovaries when compared to later developmental periods. However, Pabpc1 transcript was highly generated in the prepubertal and pubertal mouse ovaries except for 1-week old ovary than those of other developmental terms. In the prepubertal mouse ovaries, RNA in situ hybridization localized both Epab and Pabpc1 transcripts in the cytoplasm of oocytes and granulosa cells of all follicular stages. Consistently, Epab and Pabpc1 gene expression were detected in the cumulus cells and MII oocytes obtained from cumulus oocyte complexes (COCs). Ovarian follicle counting in the postnatal ovaries revealed that total number of follicles was higher in the prepubertal ovaries in comparison with later stages of development. As a result, Epab and Pabpc1 expression exhibit differences at postnatal ovary development stages and both genes are transcribed in the granulosa cells and oocytes. These findings suggest that EPAB may predominantly play roles in translational regulation of the mRNAs during early oogenesis and folliculogenesis, but PABPC1 most likely perform these roles in the later terms of ovarian development along with EPAB protein.//////////////////
Follicle stages
Comment
Alternative splicing of the mouse embryonic poly(A) binding protein (Epab) mRNA is regulated by an exonic splicing enhancer: a model for post-transcriptional control of gene expression in the oocyte. Seli E et al. (2008) Embryonic poly(A) binding protein (EPAB), expressed in oocytes and early embryos, binds and stabilizes maternal mRNAs, and mediates initiation of their translation. We identified an alternatively spliced form of Epab lacking exon 10 (c.Ex10del) and investigated the regulation of Epab mRNA alternative splicing as a model for alternative splicing in oocytes and early preimplantation embryos. Specifically, we evaluated the following mechanisms: imprinting; RNA editing and exonic splicing enhancers (ESEs). Sequence analysis led to the identification of two single nucleotide polymorphisms (SNPs): one was detected in exon 9 (rs55858A/G), and served as a marker for the parental origin of the alternatively spliced form, and the other was found in exon 10 (rs56574G/C), and co-segregated with the exon 9 SNP. We found that the presence of rs56574G in exon 10 led to the formation of an ESE, leading to efficient exclusion of exon 10. Real-time RT-PCR results revealed a 5-fold increase in the expression of the c.Ex10del alternative splicing variant in animals carrying rs56574G/G in exon 10 compared with rs56574C/C at the same locus. Our findings suggest that SNPs may alter the ratio between alternative splicing variants of oocyte-specific proteins. The role that these subtle differences play in determining individual reproductive outcome remains to be determined.//////////////////
Phenotypes
Mutations
1 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: infertile - ovarian defect Comment: Embryonic poly(A) binding protein (EPAB) is required for oocyte maturation and female fertility in mice. Guzeloglu-Kayisli O et al. Gene expression during oocyte maturation and early embryogenesis until zygotic genome activation requires translational activation of maternally-derived mRNAs. Embryonic poly(A) binding protein (EPAB) is the predominant poly(A) binding protein during this period in Xenopus, mouse, and human. In Xenopus oocytes, EPAB stabilizes maternal mRNAs and promotes their translation. To assess the role of EPAB in mammalian reproduction, we generated Epab knockout mice. While Epab-/- males and Epab+/- of both sexes were fertile, Epab-/- female mice were infertile, and could not generate embryos or mature oocytes in vivo or in vitro. Epab-/- oocytes failed to achieve translational activation of maternally-stored mRNAs upon stimulation of oocyte maturation, including Cyclin B1 and Dazl mRNAs. Microinjection of Epab mRNA into Epab-/- germinal vesicle stage oocytes did not rescue maturation, suggesting that EPAB is also required for earlier stages of oogenesis. In addition, late antral follicles in the ovaries of Epab-/- mice exhibited impaired cumulus expansion, and a 8-fold decrease in ovulation, associated with a significant down-regulation of mRNAs encoding EGF-like growth factors Areg, Ereg, and Btc, and their downstream regulators, Ptgs2, Has2, and Tnfaip6. Our findings indicate that EPAB is necessary for oogenesis, folliculogenesis, and female fertility in mice.