Reconstitution of the oocyte transcriptional network with transcription factors. Hamazaki N et al. (2020) During female germline development, oocytes become a highly specialized cell type and form a maternal cytoplasmic store of crucial factors. Oocyte growth is triggered at the transition from primordial to primary follicle and is accompanied by dynamic changes in gene expression1, but the gene regulatory network that controls oocyte growth remains unknown. Here we identify a set of transcription factors that are sufficient to trigger oocyte growth. By investigation of the changes in gene expression and functional screening using an in vitro mouse oocyte development system, we identified eight transcription factors, each of which was essential for the transition from primordial to primary follicle. Notably, enforced expression of these transcription factors swiftly converted pluripotent stem cells into oocyte-like cells that were competent for fertilization and subsequent cleavage. These transcription-factor-induced oocyte-like cells were formed without specification of primordial germ cells, epigenetic reprogramming or meiosis, and demonstrate that oocyte growth and lineage-specific de novo DNA methylation are separable from the preceding epigenetic reprogramming in primordial germ cells. This study identifies a core set of transcription factors for orchestrating oocyte growth, and provides an alternative source of ooplasm, which is a unique material for reproductive biology and medicine.//////////////////
General function
Nucleic acid binding, DNA binding, Transcription factor
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Cellular localization
Nuclear
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Ovarian function
Initiation of primordial follicle growth, Germ cell development, Oocyte maturation, Early embryo development
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TBPL2/TFIIA complex establishes the maternal transcriptome through oocyte-specific promoter usage. Yu C et al. (2020) During oocyte growth, transcription is required to create RNA and protein reserves to achieve maternal competence. During this period, the general transcription factor TATA binding protein (TBP) is replaced by its paralogue, TBPL2 (TBP2 or TRF3), which is essential for RNA polymerase II transcription. We show that in oocytes TBPL2 does not assemble into a canonical TFIID complex. Our transcript analyses demonstrate that TBPL2 mediates transcription of oocyte-expressed genes, including mRNA survey genes, as well as specific endogenous retroviral elements. Transcription start site (TSS) mapping indicates that TBPL2 has a strong preference for TATA-like motif in core promoters driving sharp TSS selection, in contrast with canonical TBP/TFIID-driven TATA-less promoters that have broader TSS architecture. Thus, we show a role for the TBPL2/TFIIA complex in the establishment of the oocyte transcriptome by using a specific TSS recognition code.//////////////////
TBP2 is a general transcription factor specialized for female germ cells. Mller F et al. ABSTRACT: The complexity of the core promoter transcription machinery has emerged as an additional level of transcription regulation that is used during vertebrate development. Recent studies, including one published in BMC Biology, provide mechanistic insights into how the TATA binding protein (TBP) and its vertebrate-specific paralog TBP2 (TRF3) switch function during the transition from the oocyte to the embryo.See research article http://www.biomedcentral.com/1741-7007/7/45.
Analysis of TATA-binding protein 2 (TBP2) and TBP expression suggests different roles for the two proteins in regulation of gene expression during oogenesis and early mouse development. Gazdag E et al. Gametogenesis, the process during which germ cells are generated is essential for reproduction. In mammals, maternal mRNA and proteins present in the oocyte are required to ensure the progression of development until the embryo activates its genome after fertilisation. It is well established that the oocyte synthesises these maternal factors during oocyte growth and then undergoes a quiescent transcriptional period that will be resumed only after fertilisation. However, the mechanisms that govern transcriptional regulation and subsequent silencing during oogenesis are not well understood. Here, we have examined the expression and localisation of the TATA-binding protein (TBP) and the related protein TBP2 (also called TRF3, TBP-related factor 3) during oogenesis and in early mouse embryos. We show that TBP is expressed in the oocytes at the beginning of folliculogenesis, but it is undetectable during further stages of oocyte development, and becomes abundant again only after fertilisation. In contrast to TBP, we found that TBP2 is highly expressed in growing oocytes during folliculogenesis, declines upon ovulation, and is almost undetectable after fertilisation by the two-cell stage. The mirroring localisation profile of TBP and TBP2 suggests different roles for the two proteins in establishing specialised programs of gene expression during oocyte development and in early mouse embryos. Analysis of mutant mouse ovaries in which oocyte-specific factors have been knocked-out suggests that TBP2 is a potential candidate for regulating transcriptional control of oogenesis. Moreover, our results obtained with oocytes lacking the oocyte-specific nuclear chaperone nucleoplasmin 2 suggest that TBP2 function may be related to non-condensed chromatin conformation.
Expression regulated by
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Ovarian localization
Oocyte
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Developmental and cell type-specific regulation of core promoter transcription factors in germ cells of frogs and mice Xiao L, et al .
This article reports on the comparative cell type-specific expression profiles of selected core promoter-associated transcription factors during gametogenesis and embryogenesis in frogs and mice. In frogs we tested TBP, TRF2/TLF, TRF3, TFIIAalphabeta, and ALF, as well as variant forms of TAFs 4, 5, and 6. Four of these factors, TRF3, TAF4L, TAF5L, and the previously-characterized ALF gene, are preferentially expressed in testis and ovary. In mice we tested TBP, TRF2/TLF, TRF3, TFIIAalphabeta, and ALF. The results showed that while ALF was present in testis and ovary, as expected, TRF3 could only be detected in the ovary. RT-PCR experiments using RNAs from microdissected ovary tissue, together with in situ hybridization analysis, showed that TRF3 and ALF genes are specifically expressed in oocytes in both adult and prepubertal animals, whereas, their somatic counterparts, TBP and TFIIAalphabeta, are present in oocytes and in surrounding somatic cells of the follicle. Furthermore, both mice and frogs displayed a reduction in TRF3 and ALF transcript levels around the time of fertilization. In mice, transcripts from these genes could again be detected at low levels in embryonic reproductive tissues, but only reached maximal levels in adult animals. Finally, the results of protein-DNA interaction assays show that all combinations of core promoter complexes can be formed in vitro using recombinant TBP, TRF3, TFIIA, and ALF, including a TRF3-ALF complex. Overall, the diverse gene regulatory patterns observed here and in earlier reports indicate precise control over which transcription factor complexes can be formed in vivo during gametogenesis and early embryogenesis.
Regulated expression of TATA-binding protein-related factor 3 (TRF3) during early embryogenesis. Yang Y et al. RNA polymerase (Pol) II transcription persists in TATA-box-binding protein (TBP)(-/-) mutant mouse embryos, indicating TBP-independent mechanisms for Pol II transcription in early development. TBP-related factor 3 (TRF3) has been proposed to substitute for TBP in TBP(-/-) mouse embryos. We examined the expression of TRF3 in maturing oocytes and early embryos and found that TRF3 was co-expressed with TBP in the meiotic oocytes and early embryos from the late one-cell stage onward. The amounts of TBP and TRF3 changed dynamically and correlated well with transcriptional activity. Chromatin immunoprecipitation (ChIP) assay revealed that different gene promoters in mouse embryonic stem (ES) cells recruited TRF3 and TBP selectively. Comparative analyses of TRF3 and TBP during cell cycle showed that both factors proceeded through cell cycle in a similar pace, except that TRF3 was slightly delayed than TBP in entering the nucleus when cells were exiting the M-phase. Data from expression and biochemical analyses therefore support the hypothesis that TRF3 plays a role in early mouse development. In addition, results from co-localization study suggest that TRF3 may be also involved in Pol I transcription.Cell Research advance online publication 23 May 2006; doi: 10.1038/sj.cr.7310064.
Follicle stages
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Phenotypes
Mutations
3 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: infertile - ovarian defect Comment: TBP2 is essential for germ cell development by regulating transcription and chromatin condensation in the oocyte. Gazdag E et al. Development of the germline requires consecutive differentiation events. Regulation of these has been associated with germ cell-specific and pluripotency-associated transcription factors, but the role of general transcription factors (GTFs) remains elusive. TATA-binding protein (TBP) is a GTF involved in transcription by all RNA polymerases. During ovarian folliculogenesis in mice the vertebrate-specific member of the TBP family, TBP2/TRF3, is expressed exclusively in oocytes. To determine TBP2 function in vivo, we generated TBP2-deficient mice. We found that Tbp2(-/-) mice are viable with no apparent phenotype. However, females lacking TBP2 are sterile due to defective folliculogenesis, altered chromatin organization, and transcriptional misregulation of key oocyte-specific genes. TBP2 binds to promoters of misregulated genes, suggesting that TBP2 directly regulates their expression. In contrast, TBP ablation in the female germline results in normal ovulation and fertilization, indicating that in these cells TBP is dispensable. We demonstrate that TBP2 is essential for the differentiation of female germ cells, and show the mutually exclusive functions of these key core promoter-binding factors, TBP and TBP2, in the mouse.
Species: human
Mutation name: type: naturally occurring fertility: infertile - ovarian defect Comment: A homozygous variant in TBPL2 was identified in women with oocyte maturation defects and infertility. Yang P et al. (2021) What are the genetic causes of oocyte maturation defects? A homozygous splicing variant (c.788 + 3A>G) in TATA-box binding protein like 2 (TBPL2) was identified as a contributory genetic factor in oocyte maturation defects. TBPL2, a vertebrate oocyte-specific general transcription factor, is essential for oocyte development. TBPL2 variants have not been studied in human oocyte maturation defects. Two infertile families characterized by oocyte maturation defects were recruited for whole-exome sequencing (WES). Genomic DNA was extracted from peripheral blood for WES analysis. Sanger sequencing was performed for data validation. Pathogenicity of variants was predicted by in silico analysis. Minigene assay and single-oocyte RNA sequencing were performed to investigate the effects of the variant on mRNA integrity and oocyte transcriptome, respectively. A homozygous splicing variant (c.788 + 3A>G) in TBPL2 was identified in two unrelated families characterized by oocyte maturation defects. Haplotype analysis indicated that the disease allele of Families 1 and 2 was independent. The variant disrupted the integrity of TBPL2 mRNA. Transcriptome sequencing of affected oocytes showed that vital genes for oocyte maturation and fertilization were widely and markedly downregulated, suggesting that a mutation in the transcriptional factor, TBPL2, led to global gene alterations in oocytes. Limitations include the lack of direct functional evidence. Owing to the scarcity of human oocyte samples, only two immature MI oocytes were obtained from the patients, and we could only investigate the effect of the mutation at the transcriptional level by high-throughput sequencing technology. No extra oocytes were obtained to assess the transcriptional activity of the mutant oocytes by immunofluorescence, or investigate the effects on the binding of TBPL2 caused by the mutation. Our findings highlight a critical role of TBPL2 in female reproduction and identify a homozygous splicing mutation in TBPL2 that might be related to defects in human oocyte maturation. This information will facilitate the genetic diagnosis of infertile individuals with repeated failures of IVF, providing a basis for genetic counseling. This study was supported by the National Key Research and Development Program of China (2018YFC1004000, 2017YFC1001504 and 2017YFC1001600), the National Natural Science Foundation of China (81871168, 31900409 and 31871509), the Foundation for Distinguished Young Scholars of Shandong Province (JQ201816), the Innovative Research Team of High-Level Local Universities in Shanghai (SSMU-ZLCX20180401) and the Fundamental Research Funds of Shandong University. The authors have no competing interests to declare. N/A.//////////////////
Species: human
Mutation name: type: naturally occurring fertility: infertile - ovarian defect Comment: A homozygous missense mutation in TBPL2 is associated with oocyte maturation arrest and degeneration. Wang Y et al. (2021) The genetic causes in most of patients with oocyte maturation arrest remain largely unknown. In this study, we identified a homozygous missense mutation in TBPL2 (TATA box binding protein like 2) in two infertile sisters with oocyte maturation arrest and degeneration from a consanguineous family by whole-exome sequencing. The TBPL2 mutation is rare and pathogenic, and impaired the transcription initiation function of the protein. Our results showed that TBPL2 might be associated with female infertility due to oocyte maturation arrest and degeneration. This article is protected by copyright. All rights reserved.//////////////////