CRL4 complex regulates mammalian oocyte survival and reprogramming by activation of TET proteins. Yu C 2013 et al.
The duration of a woman's reproductive period is determined by the size and persistence of a dormant oocyte pool. Specific oocyte genes are essential for follicle maintenance and female fertility. The mechanisms that regulate the expression of these genes are poorly understood. We found that a cullin-ring finger ligase-4 (CRL4) complex was crucial in this process. Oocyte-specific deletion of the CRL4 linker protein DDB1 or its substrate adaptor VPRBP (also known as DCAF1) caused rapid oocyte loss, premature ovarian insufficiency, and silencing of fertility maintaining genes. CRL4(VPRBP) activates the TET methylcytosine dioxygenases, which are involved in female germ cell development and zygote genome reprogramming. Hence, CRL4(VPRBP) ubiquitin ligase is a guardian of female reproductive life in germ cells and a maternal reprogramming factor after fertilization.
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NCBI Summary:
Members of the ten-eleven translocation (TET) gene family, including TET3, play a role in the DNA methylation process (Langemeijer et al., 2009 [PubMed 19923888]).[supplied by OMIM, Nov 2010]
General function
Enzyme
, Epigenetic modifications
Comment
Haploinsufficiency, but Not Defective Paternal 5mC Oxidation, Accounts for the Developmental Defects of Maternal Tet3 Knockouts. Inoue A et al. (2015) Paternal DNA demethylation in mammalian zygotes is achieved through Tet3-mediated iterative oxidation of 5-methylcytosine (5mC) coupled with replication-dependent dilution. Tet3-mediated paternal DNA demethylation is believed to play important roles in mouse development given that Tet3 heterozygous embryos derived from Tet3-deficient oocytes exhibit embryonic sublethality. Here, we demonstrate that the sublethality phenotype of the Tet3 maternal knockout mice is caused by haploinsufficiency but not defective paternal 5mC oxidation. We found that Tet3 heterozygous progenies derived from heterozygous father or mother also exhibit sublethality. Importantly, wild-type embryos reconstituted with paternal pronuclei that bypassed 5mC oxidation develop and grow to adulthood normally. Genome-scale DNA methylation analysis demonstrated that hypermethylation in maternal Tet3 knockout embryos is largely diminished by the blastocyst stage. Our study thus reveals that Tet3-mediated paternal 5mC oxidation is dispensable for mouse development and suggests the existence of a compensatory mechanism for defective 5mC oxidation in preimplantation embryos.//////////////////
Cellular localization
Cytoplasmic
Comment
Ovarian function
Germ cell development, Oogenesis, Early embryo development
, Pluripotent cell derivation
Comment
Dynamics of genomic 5-hydroxymethylcytosine during mouse oocyte growth. Sakashita A 2014 et al.
Recent studies of the demethylation process in murine zygotes have shown that 5-methylcytosine (5mC) is first converted into 5-hydroxymethylcytosine (5hmC) or further-oxidized cytosines in the paternal genome by the maternal ten-eleven translocation 3 (TET3) enzyme. This process is crucial for normal embryogenesis, and our aim was to elucidate the effect of Tet3 on the maternal genome during female germ-line development. Immunofluorescence analysis showed that 5hmC was clearly present in fully grown oocytes but not in nongrowing and early growth-stage oocytes. The 5hmC in the maternal genome was clearly detectable in DNA methyltransferase 3-like enzyme (Dnmt3L)-null oocytes and their fertilized zygotes, although Dnmt3L is essential for DNA methylation in oocytes. An analysis using an enzyme digestion-based method showed that 5hmC was present in LTR retrotransposons from the late growth period of oocytes. Quantitative RT-PCR analysis showed that Tet3 expression was enhanced during oocyte growth and exhibited an approximately 40-fold increase between nongrowing and fully grown oocytes. Our results show that 5hmC is generated since the oocyte growth stage, accompanied by up-regulation of Tet3; 5hmC is located mainly in LTR retrotransposons, indicating that 5hmC generated in growth-stage oocytes is responsible for genomewide demethylation after fertilization.
/////////////////////////Tet3 is required for normal IVF preimplantation embryos development of bovine. Cheng H et al. (2019) DNA methylation is a central epigenetic event that regulates cellular differentiation, reprogramming, and pathogenesis. DNA demethylation occurs in pre-implantation embryos and primordial germ cells (PGCs). Recent studies suggest that TET3-mediated oxidation of 5-methylcytosine (5-mC) contributes to genome-wide loss of DNA methylation, yet the mechanism of this process in bovine pre-implanted embryos has remained unknown. In this study, we analyzed the expression of Tet gene family at different stages of embryo development. The results revealed that Tet3 was highly expressed in bovine oocytes and IVF pre-implantation embryos. Knockdown of Tet3 by injection of siRNA in GV oocytes was used to assess its role in epigenetic remodeling and embryo development. The results showed that knockdown of Tet3 significantly inhibited oocyte development, maturation, fertilization and decreased subsequently cleavage and blastocyst rates. Tet3 knockdown significantly increased 5-mC levels, while the 5-hmC levels slightly declined. The q-PCR data showed that expression levels of the pluripotency genes (POU5F1 and NANOG) were significantly decreased, but the imprinted gene H19 did not change in the Tet3 knockdown group. In addition, some pluripotency genes (POU5F1 and NANOG) and repeated elements (satellite I and α-satellite) promoter regions showed hypermethylation in the Tet3 knockdown group, except the imprinted gene H19. Furthermore, the percentage of apoptotic cells and the expression levels of the pro-apoptotic gene BAX were significantly increased, while the anti-apoptotic gene BCL-2 mRNA levels were decreased in the Tet3 knockdown group. Our results indicated that Tet3 could influence expression level of the pluripotency genes through regulating the methylation status of promoter region, thus affect embryonic development. This article is protected by copyright. All rights reserved.//////////////////
Active demethylation in mouse zygotes involves cytosine deamination and base excision repair. Santos F 2013 et al.
BACKGROUND
DNA methylation in mammals is an epigenetic mark necessary for normal embryogenesis. During development active loss of methylation occurs in the male pronucleus during the first cell cycle after fertilisation. This is accompanied by major chromatin remodelling and generates a marked asymmetry between the paternal and maternal genomes. The mechanism(s) by which this is achieved implicate, among others, base excision repair (BER) components and more recently a major role for TET3 hydroxylase. To investigate these methylation dynamics further we have analysed DNA methylation and hydroxymethylation in fertilised mouse oocytes by indirect immunofluorescence (IF) and evaluated the relative contribution of different candidate factors for active demethylation in knock-out zygotes by three-dimensional imaging and IF semi-quantification.
RESULTS
We find two distinct phases of loss of paternal methylation in the zygote, one prior to and another coincident with, but not dependent on, DNA replication. TET3-mediated hydroxymethylation is limited to the replication associated second phase of demethylation. Analysis of cytosine deaminase (AID) null fertilised oocytes revealed a role for this enzyme in the second phase of loss of paternal methylation, which is independent from hydroxymethylation. Investigation into the possible repair pathways involved supports a role for AID-mediated cytosine deamination with subsequent U-G mismatch long-patch BER by UNG2 while no evidence could be found for an involvement of TDG.
CONCLUSIONS
There are two observable phases of DNA demethylation in the mouse zygote, before and coincident with DNA replication. TET3 is only involved in the second phase of loss of methylation. Cytosine deamination and long-patch BER mediated by UNG2 appear to independently contribute to this second phase of active demethylation. Further work will be necessary to elucidate the mechanism(s) involved in the first phase of active demethylation that will potentially involve activities required for early sperm chromatin remodelling.
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Replication-dependent loss of 5-hydroxymethylcytosine in mouse preimplantation embryos. Inoue A et al. Although global erasure of DNA methylation has been observed in zygotes and primordial germ cells, the responsible enzyme(s) have been elusive. The demonstration that members of the Tet (ten eleven translocation) family of proteins are capable of catalyzing conversion of 5-methylcytosine (5mC) of DNA to 5-hydroxymethylcytosine (5hmC) raises the possibility that Tet proteins may participate in this process. Indeed, recent studies have implicated the involvement of Tet3 in the conversion of 5mC to 5hmC in zygotes. This result, combined with the demonstration that Tet proteins can further oxidize 5hmC to 5-carboxylcytosine followed by excision by thymine-DNA glycosylase, raises the possibility that active demethylation may take place in a process that involves Tet3-mediated oxidation followed by base excision repair. We demonstrated by immunostaining of mitotic chromosome spreads of preimplantation embryos that the 5hmC associated with the paternal genome in zygotes is gradually lost during preimplantation development. Our study suggests that, although the conversion of 5mC to 5hmC in zygotes is an enzyme-catalyzed process, loss of 5hmC during preimplantation appears to be a DNA replication-dependent passive process.
Expression regulated by
Comment
Ovarian localization
Oocyte
Comment
Pre- and Postovulatory Aging of Murine Oocytes Affect the Transcript Level and Poly(A) Tail Length of Maternal Effect Genes. Dankert D 2014 et al.
Maternal effect genes code for oocyte proteins that are important for early embryogenesis. Transcription in oocytes does not take place from the onset of meiotic progression until zygotic genome activation. During this period, protein levels are regulated posttranscriptionally, for example by poly(A) tail length. Posttranscriptional regulation may be impaired in preovulatory and postovulatory aged oocytes, caused by delayed ovulation or delayed fertilization, respectively, and may lead to developmental defects. We investigated transcript levels and poly(A) tail length of ten maternal effect genes in in vivo- and in vitro- (follicle culture) grown oocytes after pre- and postovulatory aging. Quantitative RT-PCR was performed using random hexamer-primed cDNA to determine total transcript levels and oligo(dT)16-primed cDNA to analyze poly(A) tail length. Transcript levels of in vivo preovulatory-aged oocytes remained stable except for decreases in Brg1 and Tet3. Most genes investigated showed a tendency towards increased poly(A) content. Polyadenylation of in vitro preovulatory-aged oocytes was also increased, along with transcript level declines of Trim28, Nlrp2, Nlrp14 and Zar1. In contrast to preovulatory aging, postovulatory aging of in vivo- and in vitro-grown oocytes led to a shortening of poly(A) tails. Postovulatory aging of in vivo-grown oocytes resulted in deadenylation of Nlrp5 after 12 h, and deadenylation of 4 further genes (Tet3, Trim28, Dnmt1, Oct4) after 24 h. Similarly, transcripts of in vitro-grown oocytes were deadenylated after 12 h of postovulatory aging (Tet3, Trim28, Zfp57, Dnmt1, Nlrp5, Zar1). This impact of aging on poly(A) tail length may affect the timed translation of maternal effect gene transcripts and thereby contribute to developmental defects.
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Reprogramming of the paternal genome upon fertilization involves genome-wide oxidation of 5-methylcytosine. Iqbal K et al. Genome-wide erasure of DNA cytosine-5 methylation has been reported to occur along the paternal pronucleus in fertilized oocytes in an apparently replication-independent manner, but the mechanism of this reprogramming process has remained enigmatic. Recently, considerable amounts of 5-hydroxymethylcytosine (5hmC), most likely derived from enzymatic oxidation of 5-methylcytosine (5mC) by TET proteins, have been detected in certain mammalian tissues. 5hmC has been proposed as a potential intermediate in active DNA demethylation. Here, we show that in advanced pronuclear-stage zygotes the paternal pronucleus contains substantial amounts of 5hmC but lacks 5mC. The converse is true for the maternal pronucleus, which retains 5mC but shows little or no 5hmC signal. Importantly, 5hmC persists into mitotic one-cell, two-cell, and later cleavage-stage embryos, suggesting that 5mC oxidation is not followed immediately by genome-wide removal of 5hmC through excision repair pathways or other mechanisms. This conclusion is supported by bisulfite sequencing data, which shows only limited conversion of modified cytosines to cytosines at several gene loci. It is likely that 5mC oxidation is carried out by the Tet3 oxidase. Tet3, but not Tet1 or Tet2, was expressed at high levels in oocytes and zygotes, with rapidly declining levels at the two-cell stage. Our results show that 5mC oxidation is part of the early life cycle of mammals.
5-Hydroxymethylcytosine in the mammalian zygote is linked with epigenetic reprogramming. Wossidlo M et al. The epigenomes of early mammalian embryos are extensively reprogrammed to acquire a totipotent developmental potential. A major initial event in this reprogramming is the active loss/demethylation of 5-methylcytosine (5mC) in the zygote. Here, we report on findings that link this active demethylation to molecular mechanisms. We detect 5-hydroxymethylcytosine (5hmC) as a novel modification in mouse, bovine and rabbit zygotes. On zygotic development 5hmC accumulates in the paternal pronucleus along with a reduction of 5mC. A knockdown of the 5hmC generating dioxygenase Tet3 simultaneously affects the patterns of 5hmC and 5mC in the paternal pronucleus. This finding links the loss of 5mC to its conversion into 5hmC. The maternal pronucleus seems to be largely protected against this mechanism by PGC7/Dppa3/Stella, as in PGC7 knockout zygotes 5mC also becomes accessible to oxidation into 5hmC. In summary, our data suggest an important role of 5hmC and Tet3 for DNA methylation reprogramming processes in the mammalian zygote. Fig. 4
Follicle stages
Comment
Phenotypes
Mutations
2 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: infertile - ovarian defect Comment: The role of Tet3 DNA dioxygenase in epigenetic reprogramming by oocytes. Gu TP et al. Sperm and eggs carry distinctive epigenetic modifications that are adjusted by reprogramming after fertilization. The paternal genome in a zygote undergoes active DNA demethylation before the first mitosis. The biological significance and mechanisms of this paternal epigenome remodelling have remained unclear. Here we report that, within mouse zygotes, oxidation of 5-methylcytosine (5mC) occurs on the paternal genome, changing 5mC into 5-hydroxymethylcytosine (5hmC). Furthermore, we demonstrate that the dioxygenase Tet3 (ref. 5) is enriched specifically in the male pronucleus. In Tet3-deficient zygotes from conditional knockout mice, paternal-genome conversion of 5mC into 5hmC fails to occur and the level of 5mC remains constant. Deficiency of Tet3 also impedes the demethylation process of the paternal Oct4 and Nanog genes and delays the subsequent activation of a paternally derived Oct4 transgene in early embryos. Female mice depleted of Tet3 in the germ line show severely reduced fecundity and their heterozygous mutant offspring lacking maternal Tet3 suffer an increased incidence of developmental failure. Oocytes lacking Tet3 also seem to have a reduced ability to reprogram the injected nuclei from somatic cells. Therefore, Tet3-mediated DNA hydroxylation is involved in epigenetic reprogramming of the zygotic paternal DNA following natural fertilization and may also contribute to somatic cell nuclear reprogramming during animal cloning.
Species: mouse
Mutation name: type: null mutation fertility: embryonic lethal Comment: Maternal TET3 is dispensable for embryonic development but is required for neonatal growth. Tsukada Y et al. (2015) The development of multicellular organisms is accompanied by reprogramming of the epigenome in specific cells, with the epigenome of most cell types becoming fixed after differentiation. Genome-wide reprogramming of DNA methylation occurs in primordial germ cells and in fertilized eggs during mammalian embryogenesis. The 5-methylcytosine (5mC) content of DNA thus undergoes a marked decrease in the paternal pronucleus of mammalian zygotes. This loss of DNA methylation has been thought to be mediated by an active demethylation mechanism independent of replication and to be required for development. TET3-mediated sequential oxidation of 5mC has recently been shown to contribute to the genome-wide loss of 5mC in the paternal pronucleus of mouse zygotes. We now show that TET3 localizes not only to the paternal pronucleus but also to the maternal pronucleus and oxidizes both paternal and maternal DNA in mouse zygotes, although these phenomena are less pronounced in the female pronucleus. Genetic ablation of TET3 in oocytes had no significant effect on oocyte development, maturation, or fertilization or on pregnancy, but it resulted in neonatal sublethality. Our results thus indicate that zygotic 5mC oxidation mediated by maternal TET3 is required for neonatal growth but is not essential for development.//////////////////