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Irwin Davidson

Publications and source records attributed to Irwin Davidson.

At least 19 recordsLinked to original sources
PubMed2006

Functional interaction between the homeoprotein CDX1 and the transcriptional machinery containing the TATA-binding protein.

We have previously reported that the CDX1 homeoprotein interacts with the TATA-box binding protein (TBP) on the promoter of the glucose-6-phosphatase (G6Pase) gene. We show here that CDX1 interacts with TBP via the homeodomain and that the transcriptional activity additionally requires the N-terminal domain upstream of the homeodomain. CDX1 interacting with TBP is connected to members of the TFIID and Mediator complexes, two major elements of the general transcriptional machinery. Transcription luciferase assays performed using an altered-specificity mutant of TBP provide evidence for the functionality of the interaction between CDX1 and TBP. Unlike CDX1, CDX2 does not interact with TBP nor does it transactivate the G6Pase promoter. Swapping experiments between the domains of CDX1 and CDX2 indicate that, despite opposite functional effects of the homeoproteins on the G6Pase promoter, the N-terminal domains and homeodomains of both CDX1 and CDX2 have the intrinsic ability to activate transcription and to interact with TBP. However, the carboxy domains define the specificity of CDX1 and CDX2. Thus, intra-molecular interactions control the activity and partner recruitment of CDX1 and CDX2, leading to different molecular functions.

Binding Sites↗
PubMed2006

Changes in intranuclear chromatin architecture induce bipolar nuclear localization of histone variant H1T2 in male haploid spermatids.

Spermiogenesis entails a major biochemical and morphological restructuring of the germ cell packing the DNA into the condensed spermatid nucleus. H1T2 is a histone H1 variant selectively and transiently expressed in male haploid germ cells during spermiogenesis that specifically localizes to a chromatin domain at the apical pole under the acrosome. We explored the mechanisms determining polar localization of H1T2 in spermatids. In acrosome-deficient round spermatids of hrb -/- and gopc -/- mice, H1T2 localization is not altered, indicating that proper acrosome development is not required for specifying nuclear polarity. In contrast, in late round spermatids from trf2 -/- or hmgb2 -/- mice, a bipolar H1T2 localization was observed revealing that polarity is modified by loss of proteins specifying chromatin architecture. Our results show that intranuclear chromatin organization is critical for correct polar localization of H1T2 and that H1T2 can be a useful molecular marker revealing chromatin disorganization in spermatids.

Active Transport, Cell Nucleus↗
PubMed2006

TBP as a candidate gene for mental retardation in patients with subtelomeric 6q deletions.

Monozygotic twin brothers with a subtelomeric 6q deletion presented with mental retardation, microcephaly, seizures, an enlarged cisterna magna, dimpling at elbows, a high arched palate and a thin upper lip. The same subtelomeric deletion was detected in the mother of the patients, presenting with a milder phenotype. We narrowed down the breakpoint to a region of approximately 100 kb and estimated the size of the terminal deletion to be 1.2 Mb. This region contains four known and seven putative genes. Comparison of the deletion with other reported patients showed TBP was the most plausible candidate gene for the mental retardation in this syndrome. We verified that the TBP gene expression was halved in our patients using real-time PCR. Cognitive and behavioural tests performed on previously described heterozygous tbp mice suggested that TBP is potentially involved in cognitive development.

Abnormalities, Multiple↗
PubMed2005

New insights into TAFs as regulators of cell cycle and signaling pathways.

RNA polymerase II general transcription factor TFIID is a macromolecular complex comprising the TATA-binding protein, TBP and 13-14 evolutionary conserved TBP-associated factors, TAFs. Although genetic experiments have shown that TAFs are essential for cell cycle progression in yeast and in rapidly proliferating vertebrate cells in vitro, new experiments indicate they may be dispensible in specific developmental and physiological processes. Moreover, the TAF4 subunit of TFIID negatively regulates proliferation by inhibiting activation of the TGFbeta signalling pathway by its paralogue TAF4b. TAF4 is however essential in the retinoic acid and cAMP signalling pathways acting as a cofactor for CREB and the retinoic acid receptor, but is a negative regulator of the ATF7 transcription factor.

Animals↗
PubMed2005

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.

Animals↗
PubMed2005

Proteolytic cleavage of ALF into alpha- and beta-subunits that form homologous and heterologous complexes with somatic TFIIA and TRF2 in male germ cells.

Male germ cells specifically express paralogues of components of the general transcription apparatus including ALF a paralogue of TFIIAalpha/beta. We show that endogenous ALF is proteolytically cleaved to give alpha- and beta-subunits and we map the proteolytic cleavage site by mass spectrometry. Immunoprecipitations show that ALFalpha- and beta-subunits form a series of homologous and heterologous complexes with somatic TFIIA which is coexpressed in male germ cells. In addition, we show that ALF is coexpressed in late pachytene spermatocytes and in haploid round spermatids with transcription factor TRF2, and that these proteins form stable complexes in testis extracts. Our observations highlight how cleavage of ALF and coexpression with TFIIA and TRF2 increases the combinatorial possibilities for gene regulation at different developmental stages of spermatogenesis.

Amino Acid Sequence↗
PubMed2005

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.

Activating Transcription Factors↗
PubMed2005

Polar nuclear localization of H1T2, a histone H1 variant, required for spermatid elongation and DNA condensation during spermiogenesis.

Spermiogenesis entails a major biochemical and morphological restructuring of the germ cell involving replacement of the somatic histones by protamines packing the DNA into the condensed spermatid nucleus and elimination of the cytoplasm during the elongation phase. We describe H1T2, an histone H1 variant selectively and transiently expressed in male haploid germ cells during spermiogenesis. In round and elongating spermatids, H1T2 specifically localizes to a chromatin domain at the apical pole, revealing a polarity in the spermatid nucleus. Inactivation by homologous recombination shows that H1T2 is critical for spermiogenesis as male H1t2(-/-) mice have greatly reduced fertility. Analysis of spermiogenesis in H1t2 mutant mice shows delayed nuclear condensation and aberrant elongation. As a result, mutant spermatids are characterized by the presence of residual cytoplasm, acrosome detachment, and fragmented DNA. Hence, H1T2 is a protein required for proper cell restructuring and DNA condensation during the elongation phase of spermiogenesis.

Amino Acid Sequence↗
PubMed2004

Cell-specific nucleolar localization of TBP-related factor 2.

TATA-binding protein (TBP)-related factor 2 (TRF2) is one of four closely related RNA polymerase II transcription factors. We compared the intracellular localizations of TBP and TRF2 during the cell cycle and mitosis in HeLa cells. We show that during interphase, endogenous or exogenously expressed TRF2 is located almost exclusively in the nucleolus in HeLa or Cos cells. TRF2 localization is not affected by stress or mitotic stimuli, but TRF2 is rapidly released from the nucleolus upon inhibition of pol I transcription or treatment by RNase. These results suggest that localization of HeLa TRF2 requires a nucleolar-associated RNA species. In contrast, in 3T3 fibroblast cells, exogenously expressed TRF2 localizes to the nucleoplasm. Constitutive expression of ectopic TRF2 in 3T3 cells leads to a prolonged S phase of the cell cycle and reduced proliferation. Together with previous data, our results highlight the cell-specific localization and functions of TRF2. Furthermore, we show that during cell division, HeLa TRF2 and TBP are localized in the mitotic cytoplasm and TRF2 relocalizes into the nascent nucleoli immediately after mitosis, whereas TBP reassociates with the chromatin. Although partially contradictory results have been reported, our data are consistent with a model where only small proportion of the cellular TBP remains associated with specific promoter loci during mitosis.

3T3 Cells↗
PubMed2004

[TBP, a universal transcription factor?].

The TATA binding protein (TBP) is a subunit of several macromolecular complexes required for transcription by the three nuclear RNA polymerases. This observation led to the idea that TBP is a "universal" transcription factor. The discovery of three TBP-related factors and a macromolecular complex which lacks TBP but can support RNA polymerase II transcription in vitro has led to a reappraisal of the universal character of TBP. Several in vivo studies have rather shown that TBP plays a specific role in the activation of a subset of cellular genes controlling the cell cycle. In mammals, the aminoterminal region of TBP plays a highly selective role in the maternal immunotolerance of pregnancy.

Animals↗
PubMed2004

Testis-specific transcription mechanisms promoting male germ-cell differentiation.

Male germ-cell differentiation requires spermatogenic stage- and cell-specific gene expression that is achieved by unique chromatin remodeling, transcriptional control and the expression of testis-specific genes or isoforms. Recent findings have shown that the testis has specialized transcription complexes that coordinate the differentiation program of spermatogenesis. There are male germ cell-specific differences in the components of the general transcription machinery. These include upregulated expression of the TATA-binding protein (TBP) family and its associated cofactors. Importantly, a member of the TBP family, TBP-like factor (TLF), has a distribution pattern that is dependent on the spermatogenic cycle and is essential for spermatogenesis. Interestingly TBP-associated factor (TAF7), a factor of the transcription factor (TF)IID complex, is exchanged at a critical stage in germ cell development for the testis-specific paralogue TAF7L. A compelling amount of data has established that cAMP-response-element modulator (CREM), a transcription factor responsive to the cAMP signal transduction pathway, drives expression of key testis-specific genes. In this review we summarize recent advances in the transcription machinery that is testis-specific, gene-selective and necessary for the process of spermatogenesis.

Animals↗
PubMed2003

The intracellular localisation of TAF7L, a paralogue of transcription factor TFIID subunit TAF7, is developmentally regulated during male germ-cell differentiation.

Transcription regulation in male germ cells can involve specialised mechanisms and testis-specific paralogues of the general transcription machinery. Here we describe TAF7L, a germ-cell-specific paralogue of the TFIID subunit TAF7. TAF7L is expressed through most of the male germ-cell differentiation programme, but its intracellular localisation is dynamically regulated from cytoplasmic in spermatogonia and early spermatocytes to nuclear in late pachytene spermatocytes and haploid round spermatids. Import of TAF7L into the nucleus coincides with decreased TAF7 expression and a strong increase in nuclear TBP expression, which suggests that TAF7L replaces TAF7 as a TFIID subunit in late pachytene spermatocytes and in haploid cells. In agreement with this, biochemical experiments indicate that a subpopulation of TAF7L is tightly associated with TBP in both pachytene and haploid cells and TAF7L interacts with the TFIID subunit TAF1. We further show that TAF3, TAF4 and TAF10 are all strongly expressed in early spermatocytes, but that in contrast to TBP and TAF7L, they are downregulated in haploid cells. Hence, different subunits of the TFIID complex are regulated in distinct ways during male germ-cell differentiation. These results show for the first time how the composition of a general transcription factor such as TFIID and other TAF-containing complexes are modulated during a differentiation programme highlighting the unique nature of the transcription regulatory machinery in spermatogenesis.

Amino Acid Sequence↗
PubMed2003

TAF7 (TAFII55) plays a role in the transcription activation by c-Jun.

c-Jun is a member of the AP-1 family of transcription factors regulating expression of specific target genes in a variety of cellular processes including proliferation, stress response, and tumorigenicity. In the present study we have analyzed the mechanism of c-Jun function as a transactivator with respect to members of the basal transcription machinery, TATA-binding protein-associated factors (TAFs). We show that one member of the family, human TAF7 (formerly TAFII55), physically interacts with c-Jun through two independent interaction domains, within the N- and C-terminal part of c-Jun. Interaction in vitro correlates with enhanced transactivation function of c-Jun in HEK293 and COS cells in the presence of increasing amounts of TAF7. TAF7 interacts preferentially with DNA-bound phosphorylated c-Jun, suggesting that TAF7 represents a novel c-Jun co-activator mediating activation of AP-1 target genes in response to extracellular signals.

Animals↗
PubMed2002

RNA polymerase II transcription in murine cells lacking the TATA binding protein.

Inactivation of the murine TATA binding protein (TBP) gene by homologous recombination leads to growth arrest and apoptosis at the embryonic blastocyst stage. However, after loss of TBP, RNA polymerase II (pol II) remains in a transcriptionally active phosphorylation state, and in situ run-on experiments showed high levels of pol II transcription comparable to those of wild-type cells. In contrast, pol I and pol III transcription was arrested. Our results show a differential dependency of the RNA polymerases on TBP and provide evidence for TBP-independent pol II transcriptional mechanisms that allow reinitiation and maintenance of gene transcription in vivo.

Amanitins↗
PubMed2002

Functional analysis of the TFIID-specific yeast TAF4 (yTAF(II)48) reveals an unexpected organization of its histone-fold domain.

Yeast TFIID comprises the TATA binding protein and 14 TBP-associated factors (TAF(II)s), nine of which contain histone-fold domains (HFDs). The C-terminal region of the TFIID-specific yTAF4 (yTAF(II)48) containing the HFD shares strong sequence similarity with Drosophila (d)TAF4 (dTAF(II)110) and human TAF4 (hTAF(II)135). A structure/function analysis of yTAF4 demonstrates that the HFD, a short conserved C-terminal domain (CCTD), and the region separating them are all required for yTAF4 function. Temperature-sensitive mutations in the yTAF4 HFD alpha2 helix or the CCTD can be suppressed upon overexpression of yTAF12 (yTAF(II)68). Moreover, coexpression in Escherichia coli indicates direct yTAF4-yTAF12 heterodimerization optimally requires both the yTAF4 HFD and CCTD. The x-ray crystal structure of the orthologous hTAF4-hTAF12 histone-like heterodimer indicates that the alpha3 region within the predicted TAF4 HFD is unstructured and does not correspond to the bona fide alpha3 helix. Our functional and biochemical analysis of yTAF4, rather provides strong evidence that the HFD alpha3 helix of the TAF4 family lies within the CCTD. These results reveal an unexpected and novel HFD organization in which the alpha3 helix is separated from the alpha2 helix by an extended loop containing a conserved functional domain.

Amino Acid Sequence↗
PubMed2002

Crystal structure of a subcomplex of human transcription factor TFIID formed by TATA binding protein-associated factors hTAF4 (hTAF(II)135) and hTAF12 (hTAF(II)20).

The crystal structure is presented of a complex formed by the interacting domains from two subunits of the general transcription factor TFIID, the human TATA binding protein-associated factors hTAF4 (hTAF(II)135) and hTAF12 (hTAF(II)20). In agreement with predictions, hTAF12 forms a histone fold that is very similar to that of histone H2B, yet unexpected differences are observed between the structures of the hTAF12 interaction domain of hTAF4 and histone H2A. Most importantly, the hTAF4 fragment forms only the first two helices of a classical histone fold, which are followed by a 26-residue disordered region. This indicates that either full-length TAF4 contains an unusually long connecting loop between its second and third helix, and this helix is not required for stable interaction with TAF12, or that TAF4 represents a novel class of partial histone fold motifs. Structural models and structure-based sequence alignments support a role for TAF4b and hSTAF42/yADA1 as alternative partners for TAF12 and are consistent with the formation of nucleosome-like histone-fold octamers through interaction of TAF12 with a TAF6-TAF9 tetramer, yet argue against involvement of TAF12-containing histone-fold pairs in DNA binding.

Amino Acid Sequence↗