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 À/À 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.[Keywords: TBPL2; TRF3; TBP; Zp3; RNA Polymerase II; ovary] Supplemental material is available at http://www.genesdev.org.

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.

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.

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.

The oesophageal tonsil of the chicken is a novel member of the mucosalassociated 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.

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.

The first steps of oocyte development from primordial follicle are characterised by a 1 growth phase, when unique RNA and protein reserves are created to achieve oocyte 2 competence. During this growth, oocytes do not divide and the general transcription 3 factor TATA binding protein (TBP) is replaced by its paralogue, TBPL2 (also called TBP2 4 or TRF3), which is essential for RNA polymerase II transcription (Pol II) 1,2 . However, 5 the composition and function of transcription machinery and the regulatory mechanisms 6 mediating Pol II transcription during this developmental stage remain unknown. In 7 somatic cells, the general transcription factor TFIID, which contains TBP and 13 TBP-8 associated factors, is the first to bind gene promoters to nucleate Pol II transcription 9 initiation 3 . Here, we show that in oocytes TBPL2 does not assemble into a canonical TFIID 10 complex, while it stably associates with TFIIA via distinct TFIIA interactions when 11 compared to TBP. Our transcript analyses in wild type and Tbpl2 -/oocytes demonstrates 12 that TBPL2 mediates transcription of oocyte-expressed genes, including mRNA 13 destabilisation factors genes, as well as specific endogenous retroviral elements (ERVs). 14 Transcription start site (TSS) mapping from wild-type and Tbpl2 -/growing oocytes 15demonstrates that TBPL2 has a strong preference for TATA-like motif in gene core 16 promoters driving specific sharp TSS selection. This is in marked contrast with 17 TBP/TFIID-driven TATA-less gene promoters in preceding stages that have broad TSS 18 architecture. We anticipate that our findings describing oocyte-specific transcription 19 regulation will help to understand the mechanisms associated with primary ovarian 20 insufficiency, which constitutes a frequent cause of infertility among women. 21 22