Activation of a T-box-Otx2-Gsc gene network independent of TBP and TBP-related factors.

Embryonic development relies on activating and repressing regulatory influences that are faithfully integrated at the core promoter of individual genes. In vertebrates, the basal machinery recognizing the core promoter includes TATA-binding protein (TBP) and two TBP-related factors. In Xenopus embryos, the three TBP family factors are all essential for development and are required for expression of distinct subsets of genes. Here, we report on a non-canonical TBP family-insensitive (TFI) mechanism of transcription initiation that involves mesoderm and organizer gene expression. Using TBP family single- and triple-knockdown experiments, α-amanitin treatment, transcriptome profiling and chromatin immunoprecipitation, we found that TFI gene expression cannot be explained by functional redundancy, is supported by active transcription and shows normal recruitment of the initiating form of RNA polymerase II to the promoter. Strikingly, recruitment of Gcn5 (also known as Kat2a), a co-activator that has been implicated in transcription initiation, to TFI gene promoters is increased upon depletion of TBP family factors. TFI genes are part of a densely connected TBP family-insensitive T-box-Otx2-Gsc interaction network. The results indicate that this network of genes bound by Vegt, Eomes, Otx2 and Gsc utilizes a novel, flexible and non-canonical mechanism of transcription that does not require TBP or TBP-related factors.

TBP2 is essential for germ cell development by regulating transcription and chromatin condensation in the oocyte.

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.

The mammalian-specific Tex19.1 gene plays an essential role in spermatogenesis and placenta-supported development.

STUDY QUESTION: What is the consequence of Tex19.1 gene deletion in mice? SUMMARY ANSWER: The Tex19.1 gene is important in spermatogenesis and placenta-supported development. WHAT IS KNOWN ALREADY: Tex19.1 is expressed in embryonic stem (ES) cells, primordial germ cells (PGCs), placenta and adult gonads. Its invalidation in mice leads to a variable impairment in spermatogenesis and reduction of perinatal survival. STUDY DESIGN, SIZE, DURATION: We generated knock-out mice and ES cells and compared them with wild-type counterparts. The phenotype of the Tex19.1 knock-out mouse line was investigated during embryogenesis, fetal development and placentation as well as during adulthood. PARTICIPANTS/MATERIALS, SETTING, METHODS: We used a mouse model system to generate a mutant mouse line in which the Tex19.1 gene was deleted in the germline. We performed an extensive analysis of Tex19.1-deficient ES cells and assessed their in vivo differentiation potential by generating chimeric mice after injection of the ES cells into wild-type blastocysts. For mutant animals, a morphological characterization was performed for testes and ovaries and placenta. Finally, we characterized semen parameters of mutant animals and performed real-time RT-PCR for expression levels of retrotransposons in mutant testes and ES cells. MAIN RESULTS AND THE ROLE OF CHANCE: While Tex19.1 is not essential in ES cells, our study points out that it is important for spermatogenesis and for placenta-supported development. Furthermore, we observed an overexpression of the class II LTR-retrotransposon MMERVK10C in Tex19.1-deficient ES cells and testes. LIMITATIONS, REASONS FOR CAUTION: The Tex19.1 knock-out phenotype is variable with testis morphology ranging from severely altered (in sterile males) to almost indistinguishable compared with the control counterparts (in fertile males). This variability in the testis phenotype subsequently hampered the molecular analysis of mutant testes. Furthermore, these results were obtained in the mouse, which has a second isoform (i.e. Tex19.2), while other mammals possess only one Tex19 (e.g. in humans). WIDER IMPLICATIONS OF THE FINDINGS: The fact that one gene has a role in both placentation and spermatogenesis might open new ways of studying human pathologies that might link male fertility impairment and placenta-related pregnancy disorders. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the Centre National de la Recherche Scientifique (CNRS), the Institut National de la Santé et de la Recherche Médicale (INSERM) (Grant Avenir), the Ministère de l'Education Nationale, de l'Enseignement Supérieur et de la Recherche, the Université de Strasbourg, the Association Française contre les Myopathies (AFM) and the Fondation pour la Recherche Médicale (FRM) and Hôpitaux Universitaires de Strasbourg.The authors have nothing to disclose.

TBPL2/TFIIA complex establishes the maternal transcriptome through oocyte-specific promoter usage.

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.

Oesophageal tonsil of the chicken.

The oesophageal tonsil of the chicken is a novel member of the mucosal-associated lymphoid tissue (MALT), which is located around the entrance of the proventriculus. It consists of 6 to 8 single units, which are surrounded by a thin fibrous capsule. Each one is organised around the bottom of the longitudinal folds of the oesophagus, and serves as a 'tonsillar crypt'. Stratified squamous epithelium is infiltrated by lymphoid cells, i.e. T cells, plasma cells, macrophages, and dendritic cells, but not B cells, to form lymphoepithelium (LE). In the LE vimentin-, MHC II- and ATPase-positive cells possibly represent Langerhans' cells, but the appearance of 74.3 positive cells in the LE is unusual, because the 74.3 monoclonal antibody (mAb) recognises chicken follicular dendritic cells in the germinal centre and medulla of the bursal follicles. The subepithelial lymphoid tissue is organised into T- and B-dependent regions, which are the interfollicular areas and the germinal centres, respectively. Existence of high-endothelial venules in the interfollicular region suggests an extensive cellular connection between the oesophageal tonsil and the other lymphoid organs. In the resting oesophagus the lumen is closed, but during swallowing a bolus the crypt opens and the lymphoepithelium can be exposed to undigested food, antigens, infectious agents and vaccines. The location of the oesophageal tonsil, cranial to the stomach, may provide this organ with a unique role as compared to the other parts of the MALT; namely, it may contribute to the replication of infectious bursal disease virus (IBDV) and/or the pathogenesis of infectious bursal disease.

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.

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.