Human TAFII 105 is a cell type-specific TFIID subunit related to hTAFII130

Participation of the TBP-associated factors (TAFs) in cell differentiation

The understanding of the mechanisms that regulate gene expression to establish differentiation programs and determine cell lineages, is one of the major challenges in Developmental Biology. Besides the participation of tissue-specific transcription factors and epigenetic processes, the role of general transcription factors has been ignored. Only in recent years, there have been scarce studies that address this issue. Here, we review the studies on the biological activity of some TATA-box binding protein (TBP)-associated factors (TAFs) during the proliferation of stem/progenitor cells and their involvement in cell differentiation. Particularly, the accumulated evidence suggests that TAF4, TAF4b, TAF7L, TAF8, TAF9, and TAF10, among others, participate in nervous system development, adipogenesis, myogenesis, and epidermal differentiation; while TAF1, TAF7, TAF15 may be involved in the regulation of stem cell proliferative abilities and cell cycle progression. On the other hand, evidence suggests that TBP variants such as TBPL1 and TBPL2 might be regulating some developmental processes such as germ cell maturation and differentiation, myogenesis, or ventral specification during development. Our analysis shows that it is necessary to study in greater depth the biological function of these factors and its participation in the assembly of specific transcription complexes that contribute to the differential gene expression that gives rise to the great diversity of cell types existing in an organism. The understanding of TAFs' regulation might lead to the development of new therapies for patients which suffer from mutations, alterations, and dysregulation of these essential elements of the transcriptional machinery.

Transcriptomic Analysis Reveals That Granulocyte Colony-Stimulating Factor Trigger a Novel Signaling Pathway (TAF9-P53-TRIAP1-CASP3) to Protect Retinal Ganglion Cells after Ischemic Optic Neuropathy

Optic nerve head (ONH) infarct can result in progressive retinal ganglion cell (RGC) death. The granulocyte colony-stimulating factor (GCSF) protects the RGC after ON infarct. However, protective mechanisms of the GCSF after ONH infarct are complex and remain unclear. To investigate the complex mechanisms involved, the transcriptome profiles of the GCSF-treated retinas were examined using microarray technology. The retinal mRNA samples on days 3 and 7 post rat anterior ischemic optic neuropathy (rAION) were analyzed by microarray and bioinformatics analyses. GCSF treatment influenced 3101 genes and 3332 genes on days 3 and 7 post rAION, respectively. ONH infarct led to changes in 702 and 179 genes on days 3 and 7 post rAION, respectively. After cluster analysis, the levels of TATA box-binding protein (TBP)-associated factor were significantly reduced after ONH infarct, but these significantly increased after GCSF treatment. The network analysis revealed that TBP associated factor 9 (TAF9) can bind to P53 to induce TP53-regulated inhibitor of apoptosis 1 (TRIAP1) expression. To evaluate the function of TAF9 in RGC apoptosis, GCSF plus TAF9 siRNA-treated rats were evaluated using retrograde labeling with FluoroGold assay, TUNEL assay, and Western blotting in an rAION model. The RGC densities in the GCSF plus TAF9 siRNA-treated rAION group were 1.95-fold (central retina) and 1.75-fold (midperipheral retina) lower than that in the GCSF-treated rAION group (p < 0.05). The number of apoptotic RGC in the GCSF plus TAF9 siRNA-treated group was threefold higher than that in the GCSF-treated group (p < 0.05). Treatment with TAF9 siRNA significantly reduced GCSF-induced TP53 and TRIAP1 expression by 2.4-fold and 4.7-fold, respectively, in the rAION model. Overexpression of TAF9 significantly reduced apoptotic RGC and CASP3 levels, and induced TP53 and TRIAP1 expression in the rAION model. Therefore, we have demonstrated that GCSF modulated a new pathway, TAF9-P53-TRIAP1-CASP3, to control RGC death and survival after ON infarct.

ARMC5 is part of an RPB1-specific ubiquitin ligase implicated in adrenal hyperplasia

ARMC5 is implicated in several pathological conditions, but its function remains unknown. We have previously identified CUL3 and RPB1 (the largest subunit of RNA polymerase II (Pol II) as potential ARMC5-interacting proteins. Here, we show that ARMC5, CUL3 and RBX1 form an active E3 ligase complex specific for RPB1. ARMC5, CUL3, and RBX1 formed an active E3 specific for RPB1. Armc5 deletion caused a significant reduction in RPB1 ubiquitination and an increase in an accumulation of RPB1, and hence an enlarged Pol II pool in normal tissues and organs. The compromised RPB1 degradation did not cause generalized Pol II stalling nor depressed transcription in the adrenal glands but did result in dysregulation of a subset of genes, with most upregulated. We found RPB1 to be highly expressed in the adrenal nodules from patients with primary bilateral macronodular adrenal hyperplasia (PBMAH) harboring germline ARMC5 mutations. Mutant ARMC5 had altered binding with RPB1. In summary, we discovered that wildtype ARMC5 was part of a novel RPB1-specific E3. ARMC5 mutations resulted in an enlarged Pol II pool, which dysregulated a subset of effector genes. Such an enlarged Pol II pool and gene dysregulation was correlated to adrenal hyperplasia in humans and KO mice.

Characterization and mitigation of gene expression burden in mammalian cells

Despite recent advances in circuit engineering, the design of genetic networks in mammalian cells is still painstakingly slow and fraught with inexplicable failures. Here, we demonstrate that transiently expressed genes in mammalian cells compete for limited transcriptional and translational resources. This competition results in the coupling of otherwise independent exogenous and endogenous genes, creating a divergence between intended and actual function. Guided by a resource-aware mathematical model, we identify and engineer natural and synthetic miRNA-based incoherent feedforward loop (iFFL) circuits that mitigate gene expression burden. The implementation of these circuits features the use of endogenous miRNAs as elementary components of the engineered iFFL device, a versatile hybrid design that allows burden mitigation to be achieved across different cell-lines with minimal resource requirements. This study establishes the foundations for context-aware prediction and improvement of in vivo synthetic circuit performance, paving the way towards more rational synthetic construct design in mammalian cells.

Functional specialization of two paralogous TAF12 variants by their selective association with SAGA and TFIID transcriptional regulatory complexes

TATA box-binding protein (TBP)-associated factors (TAFs), evolutionarily conserved from yeast to humans, play a central role during transcription initiation. A subset of TAF proteins is shared in transcription factor II D (TFIID) and SAGA transcription regulatory complexes. Although higher eukaryotes contain multiple TAF variants that specify tissue- and developmental stage-specific organization of TFIID or SAGA complexes, in unicellular genomes, however, each TAF is encoded by a single gene. Surprisingly, we found that the genome of Candida albicans, the predominant human fungal pathogen, contains two paralogous TAF12 genes, CaTAF12L and CaTAF12, encoding H2B-like histone-fold domain-containing variants. Of the available fungal genome sequences, only seven other closely related diploid pathogenic Candida genomes encode the two TAF12 paralogs. Using affinity purifications from C. albicans cell extracts, we demonstrate that CaTAF12L uniquely associates with the SAGA complex and CaTAF12 associates with the TFIID complex. We further show that CaTAF12, but not CaTAF12L, is essential for C. albicans growth. Conditional depletion of the two TAF12 variant proteins caused distinct cellular and colony phenotypes. Together our results define a specialized organization of the TAF12 variants and non-redundant roles for the two TAF12 variants in the unicellular C. albicans genome.

Zooming in on Transcription Preinitiation

Class II gene transcription commences with the assembly of the Preinitiation Complex (PIC) from a plethora of proteins and protein assemblies in the nucleus, including the General Transcription Factors (GTFs), RNA polymerase II (RNA pol II), co-activators, co-repressors, and more. TFIID, a megadalton-sized multiprotein complex comprising 20 subunits, is among the first GTFs to bind the core promoter. TFIID assists in nucleating PIC formation, completed by binding of further factors in a highly regulated stepwise fashion. Recent results indicate that TFIID itself is built from distinct preformed submodules, which reside in the nucleus but also in the cytosol of cells. Here, we highlight recent insights in transcription factor assembly and the regulation of transcription preinitiation.

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Architectural models of human and yeast PIC were proposed.

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Mediator core–ITC complex structure reveals novel interactions.

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TFIID submodule residing in the cytoplasm has been discovered.

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Complex assembly emerges as key concept in transcription regulation.

The core promoter: At the heart of gene expression

The identities of different cells and tissues in multicellular organisms are determined by tightly controlled transcriptional programs that enable accurate gene expression. The mechanisms that regulate gene expression comprise diverse multiplayer molecular circuits of multiple dedicated components. The RNA polymerase II (Pol II) core promoter establishes the center of this spatiotemporally orchestrated molecular machine. Here, we discuss transcription initiation, diversity in core promoter composition, interactions of the basal transcription machinery with the core promoter, enhancer-promoter specificity, core promoter-preferential activation, enhancer RNAs, Pol II pausing, transcription termination, Pol II recycling and translation. We further discuss recent findings indicating that promoters and enhancers share similar features and may not substantially differ from each other, as previously assumed. Taken together, we review a broad spectrum of studies that highlight the importance of the core promoter and its pivotal role in the regulation of metazoan gene expression and suggest future research directions and challenges.

Structural basis of transcription initiation by RNA polymerase II

Transcription of eukaryotic protein-coding genes commences with the assembly of a conserved initiation complex, which consists of RNA polymerase II (Pol II) and the general transcription factors, at promoter DNA. After two decades of research, the structural basis of transcription initiation is emerging. Crystal structures of many components of the initiation complex have been resolved, and structural information on Pol II complexes with general transcription factors has recently been obtained. Although mechanistic details await elucidation, available data outline how Pol II cooperates with the general transcription factors to bind to and open promoter DNA, and how Pol II directs RNA synthesis and escapes from the promoter.

tBRD-1 selectively controls gene activity in the Drosophila testis and interacts with two new members of the bromodomain and extra-terminal (BET) family

Multicellular organisms have evolved specialized mechanisms to control transcription in a spatial and temporal manner. Gene activation is tightly linked to histone acetylation on lysine residues that can be recognized by bromodomains. Previously, the testis-specifically expressed bromodomain protein tBRD-1 was identified in Drosophila. Expression of tBRD-1 is restricted to highly transcriptionally active primary spermatocytes. tBRD-1 is essential for male fertility and proposed to act as a co-factor of testis-specific TATA box binding protein-associated factors (tTAFs) for testis-specific transcription. Here, we performed microarray analyses to compare the transcriptomes of tbrd-1 mutant testes and wild-type testes. Our data confirmed that tBRD-1 controls gene activity in male germ cells. Additionally, comparing the transcriptomes of tbrd-1 and tTAF mutant testes revealed a subset of common target genes. We also characterized two new members of the bromodomain and extra-terminal (BET) family, tBRD-2 and tBRD-3. In contrast to other members of the BET family in animals, both possess only a single bromodomain, a characteristic feature of plant BET family members. Immunohistology techniques not only revealed that tBRD-2 and tBRD-3 partially co-localize with tBRD-1 and tTAFs in primary spermatocytes, but also that their proper subcellular distribution was impaired in tbrd-1 and tTAF mutant testes. Treating cultured male germ cells with inhibitors showed that localization of tBRD-2 and tBRD-3 depends on the acetylation status within primary spermatocytes. Yeast two-hybrid assays and co-immunoprecipitations using fly testes protein extracts demonstrated that tBRD-1 is able to form homodimers as well as heterodimers with tBRD-2, tBRD-3, and tTAFs. These data reveal for the first time the existence of single bromodomain BET proteins in animals, as well as evidence for a complex containing tBRDs and tTAFs that regulates transcription of a subset of genes with relevance for spermiogenesis.

Diversity in TAF proteomics: consequences for cellular differentiation and migration

Development is a highly controlled process of cell proliferation and differentiation driven by mechanisms of dynamic gene regulation. Specific DNA binding factors for establishing cell- and tissue-specific transcriptional programs have been characterised in different cell and animal models. However, much less is known about the role of “core transcription machinery” during cell differentiation, given that general transcription factors and their spatiotemporally patterned activity govern different aspects of cell function. In this review, we focus on the role of TATA-box associated factor 4 (TAF4) and its functional isoforms generated by alternative splicing in controlling lineage-specific differentiation of normal mesenchymal stem cells and cancer stem cells. In the light of our recent findings, induction, control and maintenance of cell differentiation status implies diversification of the transcription initiation apparatus orchestrated by alternative splicing.

Looping back to leap forward: transcription enters a new era

Comparative genome analyses reveal that organismal complexity scales not with gene number but with gene regulation. Recent efforts indicate that the human genome likely contains hundreds of thousands of enhancers, with a typical gene embedded in a milieu of tens of enhancers. Proliferation of cis-regulatory DNAs is accompanied by increased complexity and functional diversification of transcriptional machineries recognizing distal enhancers and core promoters and by the high-order spatial organization of genetic elements. We review progress in unraveling one of the outstanding mysteries of modern biology: the dynamic communication of remote enhancers with target promoters in the specification of cellular identity.

Targeting TBP-Associated Factors in Ovarian Cancer

As ovarian tumors progress, they undergo a process of dedifferentiation, allowing adaptive changes in growth and morphology that promote metastasis and chemoresistance. Herein, we outline a hypothesis that TATA-box binding protein associated factors (TAFs), which compose the RNA Polymerase II initiation factor, TFIID, contribute to regulation of dedifferentiation states in ovarian cancer. Numerous studies demonstrate that TAFs regulate differentiation and proliferation states; their expression is typically high in pluripotent cells and reduced upon differentiation. Strikingly, TAF2 exhibits copy number increases or mRNA overexpression in 73% of high-grade serous ovarian cancers (HGSC). At the biochemical level, TAF2 directs TFIID to TATA-less promoters by contact with an Initiator element, which may lead to the deregulation of the transcriptional output of these tumor cells. TAF4, which is altered in 66% of HGSC, is crucial for the stability of the TFIID complex and helps drive dedifferentiation of mouse embryonic fibroblasts to induced pluripotent stem cells. Its ovary-enriched paralog, TAF4B, is altered in 26% of HGSC. Here, we show that TAF4B mRNA correlates with Cyclin D2 mRNA expression in human granulosa cell tumors. TAF4B may also contribute to regulation of tumor microenvironment due to its estrogen-responsiveness and ability to act as a cofactor for NFκB. Conversely, TAF9, a cofactor for p53 in regulating apoptosis, may act as a tumor suppressor in ovarian cancer, since it is downregulated or deleted in 98% of HGSC. We conclude that a greater understanding of mechanisms of transcriptional regulation that execute signals from oncogenic signaling cascades is needed in order to expand our understanding of the etiology and progression of ovarian cancer, and most importantly to identify novel targets for therapeutic intervention.

TAF13 interacts with PRC2 members and is essential for Arabidopsis seed development

TBP-Associated Factors (TAFs) are components of complexes like TFIID, TFTC, SAGA/STAGA and SMAT that are important for the activation of transcription, either by establishing the basic transcription machinery or by facilitating histone acetylation. However, in Drosophila embryos several TAFs were shown to be associated with the Polycomb Repressive Complex 1 (PRC1), even though the role of this interaction remains unclear. Here we show that in Arabidopsis TAF13 interacts with MEDEA and SWINGER, both members of a plant variant of Polycomb Repressive Complex 2 (PRC2). PRC2 variants play important roles during the plant life cycle, including seed development. The taf13 mutation causes seed defects, showing embryo arrest at the 8-16 cell stage and over-proliferation of the endosperm in the chalazal region, which is typical for Arabidopsis PRC2 mutants. Our data suggest that TAF13 functions together with PRC2 in transcriptional regulation during seed development.

Distinct regulatory mechanisms of eukaryotic transcriptional activation by SAGA and TFIID

A growing number of human diseases are linked to abnormal gene expression which is largely controlled at the level of transcriptional initiation. The gene-specific activator promotes the initiation of transcription through its interaction with one or more components of the transcriptional initiation machinery, hence leading to stimulated transcriptional initiation or activation. However, all activator proteins do not target the same component(s) of the transcriptional initiation machinery. Rather, they can have different target specificities, and thus, can lead to distinct mechanisms of transcriptional activation. Two such distinct mechanisms of transcriptional activation in yeast are mediated by the SAGA (Spt-Ada-Gcn5-Acetyltransferase) and TFIID (Transcription factor IID) complexes, and are termed as "SAGA-dependent" and "TFIID-dependent" transcriptional activation, respectively. SAGA is the target of the activator in case of SAGA-dependent transcriptional activation, while the targeting of TFIID by the activator leads to TFIID-dependent transcriptional activation. Both the SAGA and TFIID complexes are highly conserved from yeast to human, and play crucial roles in gene activation among eukaryotes. The regulatory mechanisms of eukaryotic transcriptional activation by SAGA and TFIID are discussed here. This article is part of a Special Issue entitled The 26S Proteasome: When degradation is just not enough!

Taf1 regulates Pax3 protein by monoubiquitination in skeletal muscle progenitors

Pax3 plays critical roles during developmental and postnatal myogenesis. We have previously shown that levels of Pax3 protein are regulated by monoubiquitination and proteasomal degradation during postnatal myogenesis, but none of the key regulators of the monoubiquitination process were known. Here we show that Pax3 monoubiquitination is mediated by the ubiquitin-activating/conjugating activity of Taf1, a component of the core transcriptional machinery that was recently reported to be downregulated during myogenic differentiation. We show that Taf1 binds directly to Pax3 and overexpression of Taf1 increases the level of monoubiquitinated Pax3 and its degradation by the proteasome. A decrease of Taf1 results in a decrease in Pax3 monoubiquitination, an increase in the levels of Pax3 protein, and a concomitant increase in Pax3-mediated inhibition of myogenic differentiation and myoblast migration. These results suggest that Taf1 regulates Pax3 protein levels through its ability to mediate monoubiquitination, revealing a critical interaction between two proteins that are involved in distinct aspects of myogenic differentiation. Finally, these results suggest that the components of the core transcriptional are integrally involved in the process of myogenic differentiation, acting as nodal regulators of the differentiation program.

Unexpected roles for core promoter recognition factors in cell-type-specific transcription and gene regulation

The eukaryotic core promoter recognition complex was generally thought to play an essential but passive role in the regulation of gene expression. However, recent evidence now indicates that core promoter recognition complexes together with 'non-prototypical' subunits may have a vital regulatory function in driving cell-specific programmes of transcription during development. Furthermore, new roles for components of these complexes have been identified beyond development; for example, in mediating interactions with chromatin and in maintaining active gene expression across cell divisions.

TAF4b and Jun/activating protein-1 collaborate to regulate the expression of integrin alpha6 and cancer cell migration properties

The TAF4b subunit of the transcription factor IID, which has a central role in transcription by polymerase II, is involved in promoter recognition by selective recruitment of activators. The activating protein-1 (AP-1) family members participate in oncogenic transformation via gene regulation. Utilizing immunoprecipitation of endogenous protein complexes, we documented specific interactions between Jun family members and TATA box binding protein-associated factors (TAF) in colon HT29 adenocarcinoma cells. Particularly, TAF4b and c-Jun were found to colocalize and interact in the nucleus of advanced carcinoma cells and in cells with epithelial-to-mesenchymal transition (EMT) characteristics. TAF4b was found to specifically regulate the AP-1 target gene involved in EMT integrin alpha6, thus altering related cellular properties such as migration potential. Using a chromatin immunoprecipitation approach in colon adenocarcinoma cell lines, we further identified a synergistic role for TAF4b and c-Jun and other AP-1 family members on the promoter of integrin alpha6, underlining the existence of a specific mechanism related to gene expression control. We show evidence for the first time of an interdependence of TAF4b and AP-1 family members in cell type-specific promoter recognition and initiation of transcription in the context of cancer progression and EMT.

Genetically modified mouse models for premature ovarian failure (POF)

Premature ovarian failure (POF) is a complex disorder that affects approximately 1% of women. POF is characterized by the depletion of functional ovarian follicles before the age of 40 years, and clinically, patients may present with primary amenorrhea or secondary amenorrhea. Although some genes have been hypothesized to be candidates responsible for POF, the etiology of most of the cases is idiopathic, with the underlying causes still unidentified because of the heterogeneity of the disease. In this review, we consider some mutant mouse models that exhibit phenotypes which are comparable to human POF, and we suggest that the use of these mouse models may help us to gain a better understanding of the molecular mechanisms underlying POF in humans.

Shifting players and paradigms in cell-specific transcription

Historically, developmental-stage- and tissue-specific patterns of gene expression were assumed to be determined primarily by DNA regulatory sequences and their associated activators, while the general transcription machinery including core promoter recognition complexes, coactivators, and chromatin modifiers was held to be invariant. New evidence suggests that significant changes in these general transcription factors including TFIID, BAF, and Mediator may facilitate global changes in cell-type-specific transcription.

Transforming growth factor-beta regulates basal transcriptional regulatory machinery to control cell proliferation and differentiation in cranial neural crest-derived osteoprogenitor cells

Transforming growth factor-beta (Tgf-beta) signaling is crucial for regulating craniofacial development. Loss of Tgf-beta signaling results in defects in cranial neural crest cells (CNCC), but the mechanism by which Tgf-beta signaling regulates bone formation in CNCC-derived osteogenic cells remains largely unknown. In this study, we discovered that Tgf-beta regulates the basal transcriptional regulatory machinery to control intramembranous bone development. Specifically, basal transcription factor Taf4b is down-regulated in the CNCC-derived intramembranous bone in Tgfbr2(fl/fl);Wnt1-Cre mice. Tgf-beta specifically induces Taf4b expression. Moreover, small interfering RNA knockdown of Taf4b results in decreased cell proliferation and altered osteogenic differentiation in primary mouse embryonic maxillary mesenchymal cells, as seen in Tgfbr2 mutant cells. In addition, we show that Taf1 is decreased at the osteogenic initiation stage in the maxilla of Tgfbr2 mutant mice. Furthermore, small interfering RNA knockdown of Taf4b and Taf1 together in primary mouse embryonic maxillary mesenchymal cells results in up-regulated osteogenic initiator Runx2 expression, with decreased cell proliferation and altered osteogenic differentiation. Our results indicate a critical function of Tgf-beta-mediated basal transcriptional factors in regulating osteogenic cell proliferation and differentiation in CNCC-derived osteoprogenitor cells during intramembranous bone formation.

Recent advances in understanding the structure and function of general transcription factor TFIID

The general transcription factor TFIID is a macromolecular complex comprising the TATA-binding protein (TBP) and a set of 13-14 TBP associated factors (TAFs). This review discusses biochemical, genetic and electron microscopic data acquired over the past years that provide a model for the composition, organisation and assembly of TFIID. We also revisit ideas on how TFIID is recruited to the promoters of active and possibly repressed genes. Recent observations show that recognition of acetylated and methylated histone residues by structural domains in several TAFs plays an important role. Finally, we highlight several genetic studies suggesting that TFIID is required for initiation of transcription, but not for maintaining transcription once a promoter is in an active state.

Specific variants of general transcription factors regulate germ cell development in diverse organisms

Through the reductive divisions of meiosis, sexually reproducing organisms have gained the ability to produce specialized haploid cells called germ cells that fuse to establish the diploid genome of the resulting progeny. The totipotent nature of these germ cells is highlighted by their ability to provide a single fertilized egg cell with all the genetic information necessary to develop the complete repertoire of cell types of the future organism. Thus, the production of these germ cells must be tightly regulated to ensure the continued success of the germ line in future generations. One surprising germ cell development mechanism utilizes variation of the global transcriptional machinery, such as TFIID and TFIIA. Like histone variation, general transcription factor variation serves to produce gonadal-restricted or -enriched expression of selective transcriptional regulatory factors required for establishing and/or maintaining the germ line of diverse organisms. This strategy is observed among invertebrates and vertebrates, and perhaps plants, suggesting that a common theme in germ cell evolution is the diversification of selective promoter initiation factors to regulate critical gonadal-specific programs of gene expression required for sexual reproduction. This review discusses the identification and characterization of a subset of these specialized general transcription factors in diverse organisms that share a common goal of germ line regulation through transcriptional control at its most fundamental level.

Expression analysis of TFIID in single human oocytes: new potential molecular markers of oocyte quality

Molecular characterization of human female gametes should make it easier to understand the basis of certain infertility disorders. Biologically significant mRNAs have been analysed in single oocytes to search for molecular biomarkers of oocyte quality. Initial analysis was focused on mRNA for proteins involved in cell growth and cycle control, specifically those encoding members of the general transcription apparatus such as the subunits of the general transcription factor TFIID. This heteromultimeric protein, comprising about 15 subunits, is the most important general transcription factor of the second class. These proteins are essential for the initiation of transcription of protein-coding genes, so they must be present in mature oocytes for mRNA synthesis during the first phases of embryonic development. Semi-quantitative reverse transcriptionpolymerase chain reaction was used to identify different TFIID subunits in single oocytes and to search for differences in expression as compared with control tissues. The data show that the mRNAs for most TFIID subunits are indeed synthesized in oocytes, but their expression profiles differ markedly. TATAbox-binding protein associated factor 4B (TAF4B), TAF5 and TATAbox-binding protein-like 2 (TBPL2) are expressed at higher levels in oocytes than in control tissues. It is suggested that they could be used as biomarkers of oocyte quality.

Structural changes in TAF4b-TFIID correlate with promoter selectivity

Proper ovarian development requires the cell type-specific transcription factor TAF4b, a subunit of the core promoter recognition complex TFIID. We present the 35 A structure of a cell type-specific core promoter recognition complex containing TAF4b and TAF4 (4b/4-IID), which is responsible for directing transcriptional synergy between c-Jun and Sp1 at a TAF4b target promoter. As a first step toward correlating potential structure/function relationships of the prototypic TFIID versus 4b/4-IID, we have compared their 3D structures by electron microscopy and single-particle reconstruction. These studies reveal that TAF4b incorporation into TFIID induces an open conformation at the lobe involved in TFIIA and putative activator interactions. Importantly, this open conformation correlates with differential activator-dependent transcription and promoter recognition by 4b/4-IID. By combining functional and structural analysis, we find that distinct localized structural changes in a megadalton macromolecular assembly can significantly alter its activity and lead to a TAF4b-induced reprogramming of promoter specificity.

The TATA binding protein associated factor 4b (TAF4b) mediates FSH stimulation of the IGFBP-3 promoter in cultured porcine ovarian granulosa cells

We have established the gene for IGF binding protein-3 (IGFBP-3) as a target for FSH action. FSH effects on this gene require the PKA pathway as well as the PI-3 kinase and MAPK pathways. At the IGFBP-3 promoter, FSH effects depend on a site for TATA box binding protein (TBP) and formation of a high molecular weight transcription complex. To further elucidate FSH effects on the downstream events involving the TBP site, we cloned a pig TAF4b cDNA into a P-Flag expression vector. By co-transfecting granulosa cells with the IGFBP-3 promoter, we found that TAF4b mimics and enhances FSH induction of IGFBP-3 reporter activity. Using RT-PCR we showed that FSH stimulates expression of TAF4b. This would suggest that the role of TAF4b in follicular development is regulated by FSH. TAF4b may thus be the TFIID component that binds to the TBP site on the IGFBP-3 promoter and is essential for FSH induction of IGFBP-3.

Yeast two-hybrid map of Arabidopsis TFIID

General transcription factor IID (TFIID) is a multisubunit protein complex involved in promoter recognition and is fundamental to the nucleation of the RNA polymerase II transcriptional preinitiation complex. TFIID is comprised of the TATA binding protein (TBP) and 12-15 TBP-associated factors (TAFs). While general transcription factors have been extensively studied in metazoans and yeast, little is known about the details of their structure and function in the plant kingdom. This work represents the first attempt to compare the structure of a plant TFIID complex with that determined for other organisms. While no TAF3 homolog has been observed in plants, at least one homolog has been identified for each of the remaining 14 TFIID subunits, including both TAF14 and TAF15 which have previously been shown to be unique to either yeast or humans. The presence of both TAFs 14 and 15 in plants suggests ancient roles for these proteins that were lost in metazoans and fungi, respectively. Yeast two-hybrid interaction assays resulted in a total of 65 binary interactions between putative subunits of Arabidopsis TFIID, including 26 contacts unique to plants. The interaction matrix of Arabidopsis TAFs is largely consistent with the three-lobed topological map for yeast TFIID, which suggests that the structure and composition of TFIID have been highly conserved among eukaryotes.

A sequence motif in the simian virus 40 (SV40) early core promoter affects alternative splicing of transcribed mRNA

To identify new sequence elements in the promoter that affect splicing patterns of pre-mRNAs, we analyzed effects of different promoters on alternative splicing of model reporter genes. We compared the E1a alternative splicing pattern in transcripts expressed from the full-length cytomegalovirus, SV40 early, or a hybrid cytomegalovirus/SV40 early promoter and found that the hybrid promoter improved selection of the suboptimal E1a 5'SS-1. Expressing RNA from the hybrid promoter also enhanced selection of suboptimal splice sites in other alternatively spliced reporter genes, demonstrating the generality of this effect. Unlike previously defined promoter elements shown to affect alternative splicing, which were located in the enhancer/upstream activating sequences, the motif identified in this work is positioned within the core promoter; it is comprised of eight T-residues directly upstream of the SV40 early TATA box. This motif was previously implicated in DNA bending and negative regulation of transcription. Together, these results suggest that the identity of transcription complex assembled in the core promoter-dependent fashion can affect splice site selection during pre-mRNA splicing, perhaps by influencing the processivity of transcription elongation.

MYBBP1a is a Novel Repressor of NF-κB

NF-kappaB is an inducible transcription factor activated in many different cell types by inflammatory and stress signals. The transcription of a wide variety of NF-kappaB genes is regulated by the coordinated action of transcription co-activators and co-repressors. Previously we identified Myb binding protein 1a (MYBBP1a) as an interaction partner of the transcription activation domain of RelA/p65. MYBBP1a has been shown by others to regulate various transcription factors, through largely unknown mechanisms. Here we present evidence that MYBBP1a is a novel co-repressor of NF-kappaB. MYBBP1a interacted directly with RelA/p65 and expression of MYBBP1a in cells repressed NF-kappaB dependent reporter expression but did affect neither RelA/p65 nuclear translocation nor its DNA binding activity. In vitro, MYBBP1a inhibited transcription from chromatinized templates at a step before pre-initiation complex formation. MYBBP1a was found to compete with the histone acetyl transferase co-activator, p300, for interaction with the transcription activation domain of RelA/p65. Expression levels of MYBBP1a are dependent on the cell type, and are particularly high in Jurkat T cells. These results indicate that MYBBP1a is a novel NF-kappaB co-repressor of transcription that competes with p300 and may function to regulate cell type specific genes.

The new core promoter element XCPE1 (X Core Promoter Element 1) directs activator-, mediator-, and TATA-binding protein-dependent but TFIID-independent RNA polymerase II transcription from TATA-less promoters

The core promoter is a critical DNA element required for accurate transcription and regulation of transcription. Several core promoter elements have been previously identified in eukaryotes, but those cannot account for transcription from most RNA polymerase II-transcribed genes. Additional, as-yet-unidentified core promoter elements must be present in eukaryotic genomes. From extensive analyses of the hepatitis B virus X gene promoter, here we identify a new core promoter element, XCPE1 (the X gene core promoter element 1), that drives RNA polymerase II transcription. XCPE1 is located between nucleotides -8 and +2 relative to the transcriptional start site (+1) and has a consensus sequence of G/A/T-G/C-G-T/C-G-G-G/A-A-G/C(+1)-A/C. XCPE1 shows fairly weak transcriptional activity alone but exerts significant, specific promoter activity when accompanied by activator-binding sites. XCPE1 is also found in the core promoter regions of about 1% of human genes, particularly in poorly characterized TATA-less genes. Our in vitro transcription studies suggest that the XCPE1-driven transcription can be highly active in the absence of TFIID because it can utilize either free TBP or the complete TFIID complex. Our findings suggest the possibility of the existence of a TAF1 (TFIID)-independent transcriptional initiation mechanism that may be used by a category of TATA-less promoters in higher eukaryotes.

Cryo-electron microscopy studies of human TFIID: conformational breathing in the integration of gene regulatory cues

The multisubunit transcription factor TFIID is essential for directing eukaryotic promoter recognition and mediating interactions with activators/cofactors during assembly of the preinitiation complex. Despite its central role in transcription initiation and regulation, structural knowledge of the TFIID complex has so far been largely limited to electron microscopy studies of negatively stained samples. Here, we present a cryo-electron microscopy 3D reconstruction of the large endogenous human TFIID complex. The improved cryopreservation has allowed for a more detailed definition of the structural elements in the complex and for the detection, by an extensive statistical analysis of the data, of a conformational opening and closing of the cavity central to the TFIID architecture. We propose that these density rearrangements in the structure are a likely reflection of the plasticity of the interactions between TFIID and its many partner proteins.

TAF4 nucleates a core subcomplex of TFIID and mediates activated transcription from a TATA-less promoter

Activator-dependent recruitment of TFIID initiates formation of the transcriptional preinitiation complex. TFIID binds core promoter DNA elements and directs the assembly of other general transcription factors, leading to binding of RNA polymerase II and activation of RNA synthesis. How TATA box-binding protein (TBP) and the TBP-associated factors (TAFs) are assembled into a functional TFIID complex with promoter recognition and coactivator activities in vivo remains unknown. Here, we use RNAi to knock down specific TFIID subunits in Drosophila tissue culture cells to determine which subunits are most critical for maintaining stability of TFIID in vivo. Contrary to expectations, we find that TAF4 rather than TBP or TAF1 plays the most critical role in maintaining stability of the complex. Our analysis also indicates that TAF5, TAF6, TAF9, and TAF12 play key roles in stability of the complex, whereas TBP, TAF1, TAF2, and TAF11 contribute very little to complex stability. Based on our results, we propose that holo-TFIID comprises a stable core subcomplex containing TAF4, TAF5, TAF6, TAF9, and TAF12 decorated with peripheral subunits TAF1, TAF2, TAF11, and TBP. Our initial functional studies indicate a specific and significant role for TAF1 and TAF4 in mediating transcription from a TATA-less, downstream core promoter element (DPE)-containing promoter, whereas a TATA-containing, DPE-less promoter was far less dependent on these subunits. In contrast to both TAF1 and TAF4, RNAi knockdown of TAF5 had little effect on transcription from either class of promoter. These studies significantly alter previous models for the assembly, structure, and function of TFIID.

Coactivator cross-talk specifies transcriptional output

Cells often fine-tune gene expression at the level of transcription to generate the appropriate response to a given environmental or developmental stimulus. Both positive and negative influences on gene expression must be balanced to produce the correct level of mRNA synthesis. To this end, the cell uses several classes of regulatory coactivator complexes including two central players, TFIID and Mediator (MED), in potentiating activated transcription. Both of these complexes integrate activator signals and convey them to the basal apparatus. Interestingly, many promoters require both regulatory complexes, although at first glance they may seem to be redundant. Here we have used RNA interference (RNAi) in Drosophila cells to selectively deplete subunits of the MED and TFIID complexes to dissect the contribution of each of these complexes in modulating activated transcription. We exploited the robust response of the metallothionein genes to heavy metal as a model for transcriptional activation by analyzing direct factor recruitment in both heterogeneous cell populations and at the single-cell level. Intriguingly, we find that MED and TFIID interact functionally to modulate transcriptional response to metal. The metal response element-binding transcription factor-1 (MTF-1) recruits TFIID, which then binds promoter DNA, setting up a "checkpoint complex" for the initiation of transcription that is subsequently activated upon recruitment of the MED complex. The appropriate expression level of the endogenous metallothionein genes is achieved only when the activities of these two coactivators are balanced. Surprisingly, we find that the same activator (MTF-1) requires different coactivator subunits depending on the context of the core promoter. Finally, we find that the stability of multi-subunit coactivator complexes can be compromised by loss of a single subunit, underscoring the potential for combinatorial control of transcription activation.

Cyclic AMP-dependent modification of gonad-selective TAF(II)105 in a human ovarian granulosa cell line

In response to gonadotropins, the elevated level of intracellular-cyclic AMP (cAMP) in ovarian granulosa cells triggers an ordered activation of multiple ovarian genes, which in turn promotes various ovarian functions including folliculogenesis and steroidogenesis. Identification and characterization of transcription factors that control ovarian gene expression are pivotal to the understanding of the molecular basis of the tissue-specific gene regulation programs. The recent discovery of the mouse TATA binding protein (TBP)-associated factor 105 (TAF(II)105) as a gonad-selective transcriptional co-activator strongly suggests that general transcription factors such as TFIID may play a key role in regulating tissue-specific gene expression. Here we show that the human TAF(II)105 protein is preferentially expressed in ovarian granulosa cells. We also identified a novel TAF(II)105 mRNA isoform that results from alternative exon inclusion and is predicted to encode a dominant negative mutant of TAF(II)105. Following stimulation by the adenylyl cyclase activator forskolin, TAF(II)105 in granulosa cells undergoes rapid and transient phosphorylation that is dependent upon protein kinase A (PKA). Thus, our work suggests that pre-mRNA processing and post-translational modification represent two important regulatory steps for the gonad-specific functions of human TAF(II)105.

Cell-type-selective induction of c-jun by TAF4b directs ovarian-specific transcription networks

Cell-type-selective expression of the TFIID subunit TAF(II)105 (renamed TAF4b) in the ovary is essential for proper follicle development. Although a multitude of signaling pathways required for folliculogenesis have been identified, downstream transcriptional integrators of these signals remain largely unknown. Here, we show that TAF4b controls the granulosa-cell-specific expression of the proto-oncogene c-jun, and together they regulate transcription of ovary-selective promoters. Instead of using cell-type-specific activators, our findings suggest that the coactivator TAF4b regulates the expression of tissue-specific genes, at least in part, through the cell-type-specific induction of c-jun, a ubiquitous activator. Importantly, the loss of TAF4b in ovarian granulosa cells disrupts cellular morphologies and interactions during follicle growth that likely contribute to the infertility observed in TAF4b-null female mice. These data highlight a mechanism for potentiating tissue-selective functions of the basal transcription machinery and reveal intricate networks of gene expression that orchestrate ovarian-specific functions and cell morphology.

TAF7: a possible transcription initiation check-point regulator

Transcription consists of a series of highly regulated steps: assembly of a preinitiation complex (PIC) at the promoter nucleated by TFIID, followed by initiation, elongation, and termination. The present study has focused on the role of the TFIID component, TAF7, in regulating transcription initiation. In TFIID, TAF7 binds to TAF1 and inhibits its intrinsic acetyl transferase activity. We now report that although TAF7 remains bound to TAF1 and associated with TFIID during the formation of the PIC, TAF7 dissociates from the PIC upon transcription initiation. Entry of polymerase II into the assembling PIC is associated with TAF1 and TAF7 phosphorylation, coincident with TAF7 release. We propose that the TFIID composition is dynamic and that TAF7 functions as a check-point regulator suppressing premature transcription initiation until PIC assembly is complete.

Basic mechanisms for the control of germ cell gene expression

The patterns of gene expression in spermatocytes and oocytes are quite different from those in somatic cells. The messenger RNAs produced by these cells are not only required to support germ cell development but, in the case of oocytes, they are also used for maturation, fertilization, and early embryogenesis. Recent studies have begun to provide an explanation for how germ-cell-specific programs of gene expression are generated. Part of the answer comes from the observation that germ cells express core promoter-associated regulatory factors that are different from those expressed in somatic cells. These factors supplement or replace their somatic counterparts to direct expression during meiosis and gametogenesis. In addition, germ cell transcription involves the recognition and use of specialized core promoter sequences. Finally, transcription must occur on chromosomal DNA templates that are reorganized into new chromatin-packaging configurations using alternate histone subunits. This article will review recent advances in our understanding of the factors and mechanisms that control transcription in ovary and testis and will discuss models for germ cell gene expression.

TAF4b, a TBP associated factor, is required for oocyte development and function

Development of a fertilizable oocyte is a complex process that relies on the precise temporal and spatial expression of specific genes in germ cells and in surrounding somatic cells. Since female mice null for Taf4b, a TBP associated factor, are sterile, we sought to determine when during follicular development this phenotype was first observed. At postnatal day 3, ovaries of Taf4b null females contained fewer (P < 0.01) oocytes than ovaries of wild type and heterozygous Taf4b mice. However, expression of only one somatic cell marker Foxl2 was reduced in ovaries at day 15. Despite the reduced number of follicles, many proceed to the antral stage, multiple genes associated with granulosa cell differentiation and oocyte maturation were expressed in a normal pattern, and immature Taf4b null females could be hormonally primed to ovulate and mate. However, the ovulated cumulus oocyte complexes from the Taf4b null mice had fewer (P < 0.01) cumulus cells, and the oocytes were functionally abnormal. GVBD and polar body extrusion were reduced significantly (P < 0.01). The few oocytes that were fertilized failed to progress beyond the two-cell stage of development. Thus, infertility in Taf4b null female mice is associated with defects in early follicle formation, oocyte maturation, and zygotic cleavage following ovulation and fertilization.

Transcriptional regulation of early oogenesis: in search of masters

Transcription factors in the germline play important roles in ovary formation and folliculogenesis, and control both oocyte development and somatic cell function. Factor in the germline (Figla) and newborn ovary homeobox gene (Nobox) represent a growing number of oocyte-specific transcription factors that regulate genes unique to oocytes. Studies on oocyte-specific transcription factors are important in understanding the genetic pathways essential for oogenesis, pluripotency, and embryonic development. Likely, these genes regulate reproductive life span and represent candidate genes for reproductive disorders, such as premature ovarian failure, and infertility. Therefore, oocyte-specific transcription factors, and oocyte-specific genes regulated by such factors, are attractive tissue-specific pharmacological targets to regulate human fertility.

TAF4 inactivation in embryonic fibroblasts activates TGF beta signalling and autocrine growth

We have inactivated transcription factor TFIID subunit TBP-associated factor 4 (TAF4) in mouse embryonic fibroblasts. Mutant taf4(-/-) cells are viable and contain intact TFIID comprising the related TAF4b showing that TAF4 is not an essential protein. TAF4 inactivation deregulates more than 1000 genes indicating that TFIID complexes containing TAF4 and TAF4b have distinct target gene specificities. However, taf4(-/-) cell lines have altered morphology and exhibit serum-independent autocrine growth correlated with the induced expression of several secreted mitotic factors and activators of the transforming growth factor beta signalling pathway. In addition to TAF4 inactivation, many of these genes can also be induced by overexpression of TAF4b. A competitive equilibrium between TAF4 and TAF4b therefore regulates expression of genes controlling cell proliferation. We have further identified a set of genes that are regulated both by TAF4 and upon adaptation to serum starvation and which may be important downstream mediators of serum-independent growth. Our study also shows that TAF4 is an essential cofactor for activation by the retinoic acid receptor and CREB, but not for Sp1 and the vitamin D3 receptor.

TAF9b (formerly TAF9L) is a bona fide TAF that has unique and overlapping roles with TAF9

TFIID plays a key role in transcription initiation of RNA polymerase II preinitiation complex assembly. TFIID is comprised of the TATA box binding protein (TBP) and 14 TBP-associated factors (TAFs). A second set of transcriptional regulatory multiprotein complexes containing TAFs has been described (called SAGA, TFTC, STAGA, and PCAF/GCN5). Using matrix-assisted laser desorption ionization mass spectrometry, we identified a novel TFTC subunit, human TAF9Like, encoded by a TAF9 paralogue gene. We show that TAF9Like is a subunit of TFIID, and thus, it will be called TAF9b. TFIID and TFTC complexes in which both TAF9 and TAF9b are present exist. In vitro and in vivo experiments indicate that the interactions between TAF9b and TAF6 or TAF9 and TAF6 histone fold pairs are similar. We observed a differential induction of TAF9 and TAF9b during apoptosis that, together with their different ability to stabilize p53, points to distinct requirements for the two proteins in gene regulation. Small interfering RNA (siRNA) knockdown of TAF9 and TAF9b revealed that both genes are essential for cell viability. Gene expression analysis of cells treated with either TAF9 or TAF9b siRNAs indicates that the two proteins regulate different sets of genes with only a small overlap. Taken together, these data demonstrate that TAF9 and TAF9b share some of their functions, but more importantly, they have distinct roles in the transcriptional regulatory process.

Functional characterization of core promoter elements: DPE-specific transcription requires the protein kinase CK2 and the PC4 coactivator

Downstream core promoter elements are an expanding class of regulatory sequences that add considerable diversity to the promoter architecture of RNA polymerase II-transcribed genes. We set out to determine the factors necessary for downstream promoter element (DPE)-dependent transcription and find that, against expectations, TFIID and the GTFs are not sufficient. Instead, the protein kinase CK2 and the coactivator PC4 establish DPE-specific transcription in an in vitro transcription system containing TFIID, Mediator, and the GTFs. Chromatin immunoprecipitation analyses using the DPE-dependent IRF-1 and TAF7 promoters demonstrated that CK2, and PC4 are present on these promoters in vivo. In contrast, neither PC4 nor CK2 were detected on the TAF1-dependent cyclin D promoter, which contains a DCE type of downstream element. Our findings also demonstrate that CK2 activity alters TFIID-dependent recognition of DCE sequences. These data establish that CK2 acts as a switch, converting the transcriptional machinery from functioning on one type of downstream element to another.

Identification of Novel and Cell Type Enriched Cofactors of the Transcription Activation Domain of RelA (p65 NF-κB)

RelA (NF-kappaB) is a transcription factor inducible by distinct stimuli in many different cell types. To find new cell type specific cofactors of NF-kappaB dependent transcription, we isolated RelA transcription activation domain binding proteins from the nuclear extracts of three different cell types. Analysis by electrophoresis and liquid chromatography tandem mass spectrometry identified several novel putative molecular partners. Some were strongly enriched in the complex formed from the nuclear extracts of specific cell types.

TATA-binding protein (TBP)-like factor (TLF) is a functional regulator of transcription: reciprocal regulation of the neurofibromatosis type 1 and c-fos genes by TLF/TRF2 and TBP

The lack of direct targets for TATA-binding protein (TBP)-like factors (TLFs) confounds the understanding of their role in gene expression. Here we report that human TLF (also called TBP-related factor 2 [TRF2]) activates a number of different genes, including the neurofibromatosis type 1 (NF1) gene. The overexpression of TLF increases the amount of NF1 mRNA in cells. In vivo, TLF binds to and upregulates transcription from a fragment of the NF1 promoter. In vitro, purified TLF-TFIIA binds directly to the same NF1 promoter fragment that is required for TLF responsiveness in cells. Furthermore, targeted deletion of TLF in mice reduces NF1 levels. In contrast, TLF inhibits transcription driven by a fragment from the TATA-containing c-fos promoter by sequestering TFIIA. TBP affects the NF1 and c-fos promoters in a manner reciprocal to that of TLF, stimulating the c-fos promoter and inhibiting NF1 transcription. We conclude that TLF is a functional regulator of transcription with targets distinct from those of TBP.

A functional interaction between ATF7 and TAF12 that is modulated by TAF4

The ATF7 proteins, which are members of the cyclic AMP responsive binding protein (CREB)/activating transcription factor (ATF) family of transcription factors, display quite versatile properties: they can interact with the adenovirus E1a oncoprotein, mediating part of its transcriptional activity; they heterodimerize with the Jun, Fos or related transcription factors, likely modulating their DNA-binding specificity; they also recruit to the promoter a stress-induced protein kinase (JNK2). In the present study, we investigate the functional relationships of ATF7 with hsTAF12 (formerly hsTAF(II)20/15), which has originally been identified as a component of the general transcription factor TFIID. We show that overexpression of hsTAF12 potentiates ATF7-induced transcriptional activation through direct interaction with ATF7, suggesting that TAF12 is a functional partner of ATF7. In support of this conclusion, chromatin immunoprecipitation experiments confirm the interaction of ATF7 with TAF12 on an ATF7-responsive promoter, in the absence of any artificial overexpression of both proteins. We also show that the TAF12-dependent transcriptional activation is competitively inhibited by TAF4. Although both TAF12 isoforms (TAF12-1 and -2, formerly TAF(II)20 and TAF(II)15) interact with the ATF7 activation region through their histone-fold domain, only the largest, hsTAF12-1, mediates transcriptional activation through its N-terminal region.

Follicle-stimulating hormone induction of ovarian insulin-like growth factor-binding protein-3 transcription requires a TATA box-binding protein and the protein kinase A and phosphatidylinositol-3 kinase pathways

The current study was done to elucidate the mechanism of the FSH stimulation of IGF-binding protein 3 (IGFBP-3) expression and map the FSH response element on the pig IGFBP-3 promoter. Forskolin induced IGFBP-3 reporter activity in transiently transfected granulosa cells. The protein kinase A (PKA) inhibitor [N-[2-(p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, 2HCl] (and cotransfection with a PKA inhibitor expression vector), the phosphatidylinositol-3 kinase inhibitor [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one], and the ERK inhibitor [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene], all blocked FSH stimulation. Use of serial deletion constructs and site-directed mutagenesis show that a TATA box-binding protein site is required for FSH stimulation and that a specific protein 1 (Sp1) site is required for basal transcription. Gel shift assays of nuclear protein with a -61/-25 probe detected four protein-DNA complexes, with bands I and II having significantly higher intensities in FSH-treated cells than in controls. Mutation of the Sp1 site prevented formation of bands I and II whereas mutation of the TATA box-binding protein site prevented formation of band IV. Use of specific antibodies showed that Sp1 participates in formation of band I, Sp3 band II, and p300 in both I and II. Band III was nonspecifically competed out. We conclude that FSH stimulation of IGFBP-3 transcription is mediated by cAMP via the PKA pathway and requires the P1-3 kinase and likely the MAPK pathways.

Novel isoforms of the TFIID subunit TAF4 modulate nuclear receptor-mediated transcriptional activity

The transcription factor TFIID consists of TATA-binding protein (TBP) and TBP-associated factors (TAFs). TAFs are essential for modulation of transcriptional activity but the regulation of TAFs is complex and many important aspects remain unclear. In this study, we have identified and characterized five novel truncated forms of the TFIID subunit TAF4 (TAF(II)135). Analysis of the mouse gene structure revealed that all truncations were the results of alternative splicing and resulted in the loss of domains or parts of domains implicated in TAF4 functional interactions. Results from transcriptional assays showed that several of the TAF4 isoforms exerted dominant negative effects on TAF4 activity in nuclear receptor-mediated transcriptional activation. In addition, alternative TAF4 isoforms could be detected in specific cell types. Our results indicate an additional level of complexity in TAF4-mediated regulation of transcription and suggest context-specific roles for these new TAF4 isoforms in transcriptional regulation in vivo.

The transcription network regulating melanocyte development and melanoma

The enormous variety of pigmentation phenotypes in nature reflects a series of remarkable events that begin in the neural crest and end with the manufacture and distribution of pigment by mature melanocytes located in the epidermis and hair follicles. While the origins of melanoblasts from multipotent precursors in the neural crest is striking in itself, yet more so is the fact that these pioneer melanoblasts manage to undertake and survive their long migration, and in doing so proliferate and maintain their identity before ultimately arriving at their destination and undergoing differentiation. With the application of the powerful combination of genetics and molecular and cell biology the mystery surrounding the genesis of the melanocyte lineage is slowly being unravelled. At its heart is the powerful alliance between signal transduction and transcription that coordinates the program of gene expression that confers on a cell its identity, provides its passport for migration, and instructs it in the arts of survival and timely reproduction. The realization that the proliferation and migration of melanoblasts during development resembles closely the proliferation and metastasis of melanoma, a highly dangerous and increasingly common cancer, serves to highlight the value of the melanocyte system as a model for addressing key issues of general significance in both development and cancer.

Core promoter binding by histone-like TAF complexes

A major function of TFIID is core promoter recognition. TFIID consists of TATA-binding protein (TBP) and 14 TBP-associated factors (TAFs). Most of them contain a histone fold domain (HFD) that lacks the DNA-contacting residues of histones. Whether and how TAF HFDs contribute to core promoter DNA binding are yet unresolved. Here we examined the DNA binding activity of TAF9, TAF6, TAF4b, and TAF12, which are related to histones H3, H4, H2A, and H2B, respectively. Each of these TAFs has intrinsic DNA binding activity adjacent to or within the HFD. The DNA binding domains were mapped to evolutionarily conserved and essential regions. Remarkably, HFD-mediated interaction enhanced the DNA binding activity of each of the TAF6-TAF9 and TAF4b-TAF12 pairs and of a histone-like octamer complex composed of the four TAFs. Furthermore, HFD-mediated interaction stimulated sequence-specific binding by TAF6 and TAF9. These results suggest that TAF HFDs merge with other conserved domains for efficient and specific core promoter binding.

Transcription factories: quantitative studies of nanostructures in the mammalian nucleus

Transcription by the three nuclear RNA polymerases is carried out in transcription factories. This conclusion has been drawn from estimates of the total number of nascent transcripts or active polymerase molecules and the number of transcription sites within a cell. Here we summarise the variety of methods used to determine these parameters, discuss their associated problems and outline future prospects.

Sequence and Spacing of TATA Box Elements Are Critical for Accurate Initiation from the β-Phaseolin Promoter

The beta-phaseolin (phas) gene, which encodes one of the major seed storage proteins of P. vulgaris, is tightly regulated at the transcription level resulting in strict tissue-specific and spatial expression during embryonic development. The phas proximal promoter contains a complex arrangement of core promoter elements including three TATA boxes as well as several putative initiator elements. To delineate the respective contributions of the core promoter elements to transcription initiation we have performed site-directed mutagenesis of the phas promoter. In vivo expression studies were performed on transgenic Arabidopsis harboring phas promoter mutants driving expression of the beta-glucuronidase (gus) reporter gene. Quantitative assessment of GUS activity in seeds bearing the promoter mutants indicated that both sequence and spacing of the TATA elements influenced the efficiency of transcription. Substitution, insertion or deletion mutations had no effect on histochemical staining patterns indicating that strict spacing requirements are not essential for correct spatial expression of phas during embryogenesis. Further evaluation of the phas promoter by in vitro transcription analysis revealed the presence of multiple TATA-dependent transcription initiation start sites. The distance between TATA elements and transcription start sites was maintained in insertion and deletion mutants through the creation of novel initiation sites, indicating that positioning of the TATA elements rather than DNA sequence was the primary determinant of start site location. We conclude that, while dispensable for proper spatial distribution, the complex architecture of the phas promoter is required to ensure high levels of accurate phas transcription initiation in the developing embryo.