Identification of a novel slow-muscle-fiber enhancer binding protein, MusTRD1

Transcriptional regulatory region and DNA methylation analysis of TNNI1 gene promoters in Gaoyou duck skeletal muscle (Anas platyrhynchos domestica)

1. The slow skeletal muscle troponin I (TNNI1) gene has been found to be specifically expressed in slow muscle fibres and plays an important role in muscle development. The aim of this study was to determine the active control area of duck TNNI1 and identify the potential cis-regulatory elements in the promoter. 2. In this study, the TNNI1 promoter was first cloned by genome walking and the sequences were analysed using bioinformatics software. Firefly luciferase reporter gene vectors, driven by a series of constructs with progressive deletions, were used to identify the core transcriptional regulatory region of the duck TNNI1 gene. The methylation status of the CpG island in the TNNI1 promoter was detected in skeletal muscle on embryonic days 21 and 27, by bisulphite sequencing PCR (BSP). 3. The results showed two CpG islands presented in the promoter region, with one of the CpG islands located in the core transcriptional regulatory region (-2078/-885 bp). The total methylation levels of the 14 CpG sites were not altered between breast and leg muscles on embryonic days 21 and 27. However, four CpG sites (loci of positions 4, 11, 13, and 14) showed dramatically different methylation levels between breast and leg muscles at embryonic days 21 and 27. Analysis showed that multiple CpG sites had a significant correlation between the methylation levels of the CpG sites and mRNA expressions in skeletal muscle. Multiple transcription factor binding sites including Sp1, c-Myc, Oct-1 and NF-kB motifs were identified and might be responsible for transcriptional regulation of the TNNI1 gene. 4. These findings contribute to further understanding of the fundamental mechanism for transcriptional regulation of the TNNI1 gene in ducks.

TFII-I and AP2α Co-Occupy the Promoters of Key Regulatory Genes Associated with Craniofacial Development

OBJECTIVES

The aim of this study is to define the candidate target genes for TFII-I and AP2α regulation in neural crest progenitor cells.

DESIGN

The GTF2I and GTF2IRD1 genes encoding the TFII-I family of transcription factors are prime candidates for the Williams-Beuren syndrome, a complex multisystem disorder characterized by craniofacial, skeletal, and neurocognitive deficiencies. AP2α, a product of the TFAP2A gene, is a master regulator of neural crest cell lineage. Mutations in TFAP2A cause branchio-oculo-facial syndrome characterized by dysmorphic facial features and orofacial clefts. In this study, we examined the genome-wide promoter occupancy of TFII-I and AP2α in neural crest progenitor cells derived from in vitro-differentiated human embryonic stem cells.

RESULTS

Our study revealed that TFII-I and AP2α co-occupy a selective set of genes that control the specification of neural crest cells.

CONCLUSIONS

The data suggest that TFII-I and AP2α may coordinately control the expression of genes encoding chromatin-modifying proteins, epigenetic enzymes, transcription factors, and signaling proteins.

RNA-Seq analysis of Gtf2ird1 knockout epidermal tissue provides potential insights into molecular mechanisms underpinning Williams-Beuren syndrome

BACKGROUND

Williams-Beuren Syndrome (WBS) is a genetic disorder associated with multisystemic abnormalities, including craniofacial dysmorphology and cognitive defects. It is caused by a hemizygous microdeletion involving up to 28 genes in chromosome 7q11.23. Genotype/phenotype analysis of atypical microdeletions implicates two evolutionary-related transcription factors, GTF2I and GTF2IRD1, as prime candidates for the cause of the facial dysmorphology.

RESULTS

Using a targeted Gtf2ird1 knockout mouse, we employed massively-parallel sequencing of mRNA (RNA-Seq) to understand changes in the transcriptional landscape associated with inactivation of Gtf2ird1 in lip tissue. We found widespread dysregulation of genes including differential expression of 78 transcription factors or coactivators, several involved in organ development including Hey1, Myf6, Myog, Dlx2, Gli1, Gli2, Lhx2, Pou3f3, Sox2, Foxp3. We also found that the absence of GTF2IRD1 is associated with increased expression of genes involved in cellular proliferation, including growth factors consistent with the observed phenotype of extreme thickening of the epidermis. At the same time, there was a decrease in the expression of genes involved in other signalling mechanisms, including the Wnt pathway, indicating dysregulation in the complex networks necessary for epidermal differentiation and facial skin patterning. Several of the differentially expressed genes have known roles in both tissue development and neurological function, such as the transcription factor Lhx2 which regulates several genes involved in both skin and brain development.

CONCLUSIONS

Gtf2ird1 inactivation results in widespread gene dysregulation, some of which may be due to the secondary consequences of gene regulatory network disruptions involving several transcription factors and signalling molecules. Genes involved in growth factor signalling and cell cycle progression were identified as particularly important for explaining the skin dysmorphology observed in this mouse model. We have noted that a number of the dysregulated genes have known roles in brain development as well as epidermal differentiation and maintenance. Therefore, this study provides clues as to the underlying mechanisms that may be involved in the broader profile of WBS.

The nuclear localization pattern and interaction partners of GTF2IRD1 demonstrate a role in chromatin regulation

GTF2IRD1 is one of the three members of the GTF2I gene family, clustered on chromosome 7 within a 1.8 Mb region that is prone to duplications and deletions in humans. Hemizygous deletions cause Williams-Beuren syndrome (WBS) and duplications cause WBS duplication syndrome. These copy number variations disturb a variety of developmental systems and neurological functions. Human mapping data and analyses of knockout mice show that GTF2IRD1 and GTF2I underpin the craniofacial abnormalities, mental retardation, visuospatial deficits and hypersociability of WBS. However, the cellular role of the GTF2IRD1 protein is poorly understood due to its very low abundance and a paucity of reagents. Here, for the first time, we show that endogenous GTF2IRD1 has a punctate pattern in the nuclei of cultured human cell lines and neurons. To probe the functional relationships of GTF2IRD1 in an unbiased manner, yeast two-hybrid libraries were screened, isolating 38 novel interaction partners, which were validated in mammalian cell lines. These relationships illustrate GTF2IRD1 function, as the isolated partners are mostly involved in chromatin modification and transcriptional regulation, whilst others indicate an unexpected role in connection with the primary cilium. Mapping of the sites of protein interaction also indicates key features regarding the evolution of the GTF2IRD1 protein. These data provide a visual and molecular basis for GTF2IRD1 nuclear function that will lead to an understanding of its role in brain, behaviour and human disease.

The transcription factor GTF2IRD1 regulates the topology and function of photoreceptors by modulating photoreceptor gene expression across the retina

The mechanisms that specify photoreceptor cell-fate determination, especially as regards to short-wave-sensitive (S) versus medium-wave-sensitive (M) cone identity, and maintain their nature and function, are not fully understood. Here we report the importance of general transcription factor II-I repeat domain-containing protein 1 (GTF2IRD1) in maintaining M cone cell identity and function as well as rod function. In the mouse, GTF2IRD1 is expressed in cell-fate determined photoreceptors at postnatal day 10. GTF2IRD1 binds to enhancer and promoter regions in the mouse rhodopsin, M- and S-opsin genes, but regulates their expression differentially. Through interaction with the transcription factors CRX and thyroid hormone receptor β 2, it enhances M-opsin expression, whereas it suppresses S-opsin expression; and with CRX and NRL, it enhances rhodopsin expression. In an apparent paradox, although GTF2IRD1 is widely expressed in multiple cell types across the retina, knock-out of GTF2IRD1 alters the retinal expression of only a limited number of annotated genes. Interestingly, however, the null mutation leads to altered topology of cone opsin expression in the retina, with aberrant S-opsin overexpression and M-opsin underexpression in M cones. Gtf2ird1-null mice also demonstrate abnormal M cone and rod electrophysiological responses. These findings suggest an important role for GTF2IRD1 in regulating the level and topology of rod and cone gene expression, and in maintaining normal retinal function.

MEF2 transcription factors regulate distinct gene programs in mammalian skeletal muscle differentiation

Skeletal muscle differentiation requires precisely coordinated transcriptional regulation of diverse gene programs that ultimately give rise to the specialized properties of this cell type. In Drosophila, this process is controlled, in part, by MEF2, the sole member of an evolutionarily conserved transcription factor family. By contrast, vertebrate MEF2 is encoded by four distinct genes, Mef2a, -b, -c, and -d, making it far more challenging to link this transcription factor to the regulation of specific muscle gene programs. Here, we have taken the first step in molecularly dissecting vertebrate MEF2 transcriptional function in skeletal muscle differentiation by depleting individual MEF2 proteins in myoblasts. Whereas MEF2A is absolutely required for proper myoblast differentiation, MEF2B, -C, and -D were found to be dispensable for this process. Furthermore, despite the extensive redundancy, we show that mammalian MEF2 proteins regulate a significant subset of nonoverlapping gene programs. These results suggest that individual MEF2 family members are able to recognize specific targets among the entire cohort of MEF2-regulated genes in the muscle genome. These findings provide opportunities to modulate the activity of MEF2 isoforms and their respective gene programs in skeletal muscle homeostasis and disease.

The role of GTF2IRD1 in the auditory pathology of Williams-Beuren Syndrome

Williams-Beuren Syndrome (WBS) is a rare genetic condition caused by a hemizygous deletion involving up to 28 genes within chromosome 7q11.23. Among the spectrum of physical and neurological defects in WBS, it is common to find a distinctive response to sound stimuli that includes extreme adverse reactions to loud, or sudden sounds and a fascination with certain sounds that may manifest as strengths in musical ability. However, hearing tests indicate that sensorineural hearing loss (SNHL) is frequently found in WBS patients. The functional and genetic basis of this unusual auditory phenotype is currently unknown. Here, we investigated the potential involvement of GTF2IRD1, a transcription factor encoded by a gene located within the WBS deletion that has been implicated as a contributor to the WBS assorted neurocognitive profile and craniofacial abnormalities. Using Gtf2ird1 knockout mice, we have analysed the expression of the gene in the inner ear and examined hearing capacity by evaluating the auditory brainstem response (ABR) and the distortion product of otoacoustic emissions (DPOAE). Our results show that Gtf2ird1 is expressed in a number of cell types within the cochlea, and Gtf2ird1 null mice showed higher auditory thresholds (hypoacusis) in both ABR and DPOAE hearing assessments. These data indicate that the principal hearing deficit in the mice can be traced to impairments in the amplification process mediated by the outer hair cells and suggests that similar mechanisms may underpin the SNHL experienced by WBS patients.

Epigenetic modulation by TFII-I during embryonic stem cell differentiation

TFII-I transcription factors play an essential role during early vertebrate embryogenesis. Genome-wide mapping studies by ChIP-seq and ChIP-chip revealed that TFII-I primes multiple genomic loci in mouse embryonic stem cells and embryonic tissues. Moreover, many TFII-I-bound regions co-localize with H3K4me3/K27me3 bivalent chromatin within the promoters of lineage-specific genes. This minireview provides a summary of current knowledge regarding the function of TFII-I in epigenetic control of stem cell differentiation.

ChIP-Chip Identifies SEC23A, CFDP1, and NSD1 as TFII-I Target Genes in Human Neural Crest Progenitor Cells

Objectives :  GTF2I and GTF2IRD1 genes located in Williams-Beuren syndrome (WBS) critical region encode TFII-I family transcription factors. The aim of this study was to map genomic sites bound by these proteins across promoter regions of developmental regulators associated with craniofacial development. Design :  Chromatin was isolated from human neural crest progenitor cells and the DNA-binding profile was generated using the human RefSeq tiling promoter ChIP-chip arrays. Results :  TFII-I transcription factors are recruited to the promoters of SEC23A, CFDP1, and NSD1 previously defined as TFII-I target genes. Moreover, our analysis revealed additional binding elements that contain E-boxes and initiator-like motifs. Conclusions :  Genome-wide promoter binding studies revealed SEC23A, CFDP1, and NSD1 linked to craniofacial or dental development as direct TFII-I targets. Developmental regulation of these genes by TFII-I factors could contribute to the WBS-specific facial dysmorphism.

Diversity and complexity in chromatin recognition by TFII-I transcription factors in pluripotent embryonic stem cells and embryonic tissues

GTF2I and GTF2IRD1 encode a family of closely related transcription factors TFII-I and BEN critical in embryonic development. Both genes are deleted in Williams-Beuren syndrome, a complex genetic disorder associated with neurocognitive, craniofacial, dental and skeletal abnormalities. Although genome-wide promoter analysis has revealed the existence of multiple TFII-I binding sites in embryonic stem cells (ESCs), there was no correlation between TFII-I occupancy and gene expression. Surprisingly, TFII-I recognizes the promoter sequences enriched for H3K4me3/K27me3 bivalent domain, an epigenetic signature of developmentally important genes. Moreover, we discovered significant differences in the association between TFII-I and BEN with the cis-regulatory elements in ESCs and embryonic craniofacial tissues. Our data indicate that in embryonic tissues BEN, but not the highly homologous TFII-I, is primarily recruited to target gene promoters. We propose a “feed-forward model” of gene regulation to explain the specificity of promoter recognition by TFII-I factors in eukaryotic cells.

GTF2IRD2 from the Williams-Beuren critical region encodes a mobile-element-derived fusion protein that antagonizes the action of its related family members

GTF2IRD2 belongs to a family of transcriptional regulators (including TFII-I and GTF2IRD1) that are responsible for many of the key features of Williams-Beuren syndrome (WBS). Sequence evidence suggests that GTF2IRD2 arose in eutherian mammals by duplication and divergence from the gene encoding TFII-I. However, in GTF2IRD2, most of the C-terminal domain has been lost and replaced by the domesticated remnant of an in-frame hAT-transposon mobile element. In this first experimental analysis of function, we show that transgenic expression of each of the three family members in skeletal muscle causes significant fiber type shifts, but the GTF2IRD2 protein causes an extreme shift in the opposite direction to the two other family members. Mating of GTF2IRD1 and GTF2IRD2 mice restores the fiber type balance, indicating an antagonistic relationship between these two paralogs. In cells, GTF2IRD2 localizes to cytoplasmic microtubules and discrete speckles in the nuclear periphery. We show that it can interact directly with TFII-Iβ and GTF2IRD1, and upon co-transfection changes the normal distribution of these two proteins into a punctate nuclear pattern typical of GTF2IRD2. These data suggest that GTF2IRD2 has evolved as a regulator of GTF2IRD1 and TFII-I; inhibiting their function by direct interaction and sequestration into inactive nuclear zones.

Global analysis of gene expression in the developing brain of Gtf2ird1 knockout mice

Background

Williams-Beuren Syndrome (WBS) is a neurodevelopmental disorder caused by a hemizygous deletion of a 1.5 Mb region on chromosome 7q11.23 encompassing 26 genes. One of these genes, GTF2IRD1, codes for a putative transcription factor that is expressed throughout the brain during development. Genotype-phenotype studies in patients with atypical deletions of 7q11.23 implicate this gene in the neurological features of WBS, and Gtf2ird1 knockout mice show reduced innate fear and increased sociability, consistent with features of WBS. Multiple studies have identified in vitro target genes of GTF2IRD1, but we sought to identify in vivo targets in the mouse brain.

Methodology/Principal Findings

We performed the first in vivo microarray screen for transcriptional targets of Gtf2ird1 in brain tissue from Gtf2ird1 knockout and wildtype mice at embryonic day 15.5 and at birth. Changes in gene expression in the mutant mice were moderate (0.5 to 2.5 fold) and of candidate genes with altered expression verified using real-time PCR, most were located on chromosome 5, within 10 Mb of Gtf2ird1. siRNA knock-down of Gtf2ird1 in two mouse neuronal cell lines failed to identify changes in expression of any of the genes identified from the microarray and subsequent analysis showed that differences in expression of genes on chromosome 5 were the result of retention of that chromosome region from the targeted embryonic stem cell line, and so were dependent upon strain rather than Gtf2ird1 genotype. In addition, specific analysis of genes previously identified as direct in vitro targets of GTF2IRD1 failed to show altered expression.

Conclusions/Significance

We have been unable to identify any in vivo neuronal targets of GTF2IRD1 through genome-wide expression analysis, despite widespread and robust expression of this protein in the developing rodent brain.

Excitation-transcription coupling in skeletal muscle: the molecular pathways of exercise

Muscle fibres have different properties with respect to force, contraction speed, endurance, oxidative/glycolytic capacity etc. Although adult muscle fibres are normally post-mitotic with little turnover of cells, the physiological properties of the pre-existing fibres can be changed in the adult animal upon changes in usage such as after exercise. The signal to change is mainly conveyed by alterations in the patterns of nerve-evoked electrical activity, and is to a large extent due to switches in the expression of genes. Thus, an excitation-transcription coupling must exist. It is suggested that changes in nerve-evoked muscle activity lead to a variety of activity correlates such as increases in free intracellular Ca²⁺ levels caused by influx across the cell membrane and/or release from the sarcoplasmatic reticulum, concentrations of metabolites such as lipids and ADP, hypoxia and mechanical stress. Such correlates are detected by sensors such as protein kinase C (PKC), calmodulin, AMP-activated kinase (AMPK), peroxisome proliferator-activated receptor δ (PPARδ), and oxygen dependent prolyl hydroxylases that trigger intracellular signaling cascades. These complex cascades involve several transcription factors such as nuclear factor of activated T-cells (NFAT), myocyte enhancer factor 2 (MEF2), myogenic differentiation factor (myoD), myogenin, PPARδ, and sine oculis homeobox 1/eyes absent 1 (Six1/Eya1). These factors might act indirectly by inducing gene products that act back on the cascade, or as ultimate transcription factors binding to and transactivating/repressing genes for the fast and slow isoforms of various contractile proteins and of metabolic enzymes. The determination of size and force is even more complex as this involves not only intracellular signaling within the muscle fibres, but also muscle stem cells called satellite cells. Intercellular signaling substances such as myostatin and insulin-like growth factor 1 (IGF-1) seem to act in a paracrine fashion. Induction of hypertrophy is accompanied by the satellite cells fusing to myofibres and thereby increasing the capacity for protein synthesis. These extra nuclei seem to remain part of the fibre even during subsequent atrophy as a form of muscle memory facilitating retraining. In addition to changes in myonuclear number during hypertrophy, changes in muscle fibre size seem to be caused by alterations in transcription, translation (per nucleus) and protein degradation.

Enhanced prefrontal serotonin 5-HT(1A) currents in a mouse model of Williams-Beuren syndrome with low innate anxiety

Williams-Beuren syndrome (WBS) is a neurodevelopmental disorder caused by the hemizygous deletion of 28 genes on chromosome 7, including the general transcription factor GTF2IRD1. Mice either hemizygously (Gtf2ird1(+/-)) or homozygously (Gtf2ird1(-/-)) deleted for this transcription factor exhibit low innate anxiety, low aggression and increased social interaction, a phenotype that shares similarities to the high sociability and disinhibition seen in individuals with WBS. Here, we investigated the inhibitory effects of serotonin (5-HT) on the major output neurons of the prefrontal cortex in Gtf2ird1(-/-) mice and their wildtype (WT) siblings. Prefrontal 5-HT receptors are known to modulate anxiety-like behaviors, and the Gtf2ird1(-/-) mice have altered 5-HT metabolism in prefrontal cortex. Using whole cell recording from layer V neurons in acute brain slices of prefrontal cortex, we found that 5-HT elicited significantly larger inhibitory, outward currents in Gtf2ird1(-/-) mice than in WT controls. In both genotypes, these currents were resistant to action potential blockade with TTX and were suppressed by the selective 5-HT(1A) receptor antagonist WAY-100635, suggesting that they are mediated directly by 5-HT(1A) receptors on the recorded neurons. Control experiments suggest a degree of layer and receptor specificity in this enhancement since 5-HT(1A) receptor-mediated responses in layer II/III pyramidal neurons were unchanged as were responses mediated by two other inhibitory receptors in layer V pyramidal neurons. Furthermore, we demonstrate GTF2IRD1 protein expression by neurons in layer V of the prefrontal cortex. Our finding that 5-HT(1A)-mediated responses are selectively enhanced in layer V pyramidal neurons of Gtf2ird1(-/-) mice gives insight into the cellular mechanisms that underlie reduced innate anxiety and increased sociability in these mice, and may be relevant to the low social anxiety and disinhibition in patients with WBS and their sensitivity to serotonergic medicines. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11689-010-9044-5) contains supplementary material, which is available to authorized users.

Negative autoregulation of GTF2IRD1 in Williams-Beuren syndrome via a novel DNA binding mechanism

The GTF2IRD1 gene is of principal interest to the study of Williams-Beuren syndrome (WBS). This neurodevelopmental disorder results from the hemizygous deletion of a region of chromosome 7q11.23 containing 28 genes including GTF2IRD1. WBS is thought to be caused by haploinsufficiency of certain dosage-sensitive genes within the deleted region, and the feature of supravalvular aortic stenosis (SVAS) has been attributed to reduced elastin caused by deletion of ELN. Human genetic mapping data have implicated two related genes GTF2IRD1 and GTF2I in the cause of some the key features of WBS, including craniofacial dysmorphology, hypersociability, and visuospatial deficits. Mice with mutations of the Gtf2ird1 allele show evidence of craniofacial abnormalities and behavioral changes. Here we show the existence of a negative autoregulatory mechanism that controls the level of GTF2IRD1 transcription via direct binding of the GTF2IRD1 protein to a highly conserved region of the GTF2IRD1 promoter containing an array of three binding sites. The affinity for this protein-DNA interaction is critically dependent upon multiple interactions between separate domains of the protein and at least two of the DNA binding sites. This autoregulatory mechanism leads to dosage compensation of GTF2IRD1 transcription in WBS patients. The GTF2IRD1 promoter represents the first established in vivo gene target of the GTF2IRD1 protein, and we use it to model its DNA interaction capabilities.

Determination and functional analysis of the consensus binding site for TFII-I family member BEN, implicated in Williams-Beuren syndrome

The ubiquitously expressed TFII-I family of multifunctional transcription factors is involved in gene regulation as well as signaling. Despite the fact that they share significant sequence homology, these factors exhibit varied and distinct functions. The lack of knowledge about its binding sites and physiological target genes makes it more difficult to assign a definitive function for the TFII-I-related protein, BEN. We set out to determine its optimal binding site with the notion of predicting its physiological target genes. Here we report the identification of an optimal binding sequence for BEN by SELEX (systematic evolution of ligands by exponential enrichment) and confirm the relevance of this sequence by functional assays. We further performed a data base search to assign genes that have this consensus site(s) and validate several candidate genes by quantitative PCR upon stable silencing of BEN and by chromatin immunoprecipitation assay upon stable expression of BEN. Given that haploinsufficiency in BEN is causative to Williams-Beuren syndrome, these results may further lead to the identification of a set of physiologically relevant target genes for BEN and may help identify molecular determinants of Williams-Beuren syndrome.

TFII-I gene family during tooth development: candidate genes for tooth anomalies in Williams syndrome

Williams syndrome is a rare congenital disorder involving the cardiovascular system, mental retardation, distinctive facial features, and tooth anomalies. It is caused by the heterozygous deletion of approximately 1.6 Mb encompassing 28 genes on human chromosome 7q11.23. It has been suggested that the genes responsible for craniofacial anomalies are located in the telomeric end region, which harbors three members of the TFII-I gene family (Tassabehji et al. [2005] Science 310:1184). To recognize potential candidate genes for the tooth anomalies in Williams syndrome, we carried out comparative in situ hybridization analysis of members of TFII-I gene family during murine odontogenesis. Gtf2i showed widespread expression in the developing head but was higher in the developing teeth than surrounding tissues throughout tooth development. At the bud stage, Gtf2ird1 and Gtf2ird2 were expressed in the epithelial buds. At the early bell stage, expression of Gtf2ird1 and Gtf2ird2 was observed in preameloblasts and preodontoblasts.

GTF2IRD1 regulates transcription by binding an evolutionarily conserved DNA motif ‘GUCE’

GTF2IRD1 is a member of a family of transcription factors whose defining characteristic is varying numbers of a helix-loop-helix like motif, the I-repeat. Here, we present functional analysis of human GTF2IRD1 in regulation of three genes (HOXC8, GOOSECOID and TROPONIN I(SLOW)). We define a regulatory motif (GUCE-GTF2IRD1 Upstream Control Element) common to all three genes. GUCE is bound in vitro by domain I-4 of GTF2IRD1 and mediates transcriptional regulation by GTF2IRD1 in vivo. Definition of this site will assist in identification of other downstream targets of GTF2IRD1 and elucidation of its role in the human developmental disorder Williams-Beuren syndrome.

Expression profiling of BEN regulated genes in mouse embryonic fibroblasts

BEN is a member of the TFII-I family of helix-loop-helix transcription factors. Both TFII-I and BEN are involved in gene regulation through interactions with tissue-specific transcription factors and chromatin remodeling complexes. Identification of the downstream target genes of TFII-I proteins is critical in delineating the regulatory effects of these proteins. In this study, we conducted a microarray analysis to determine gene expression alterations following the overexpression of BEN in primary mouse embryonic fibroblasts (MEFs). We found the BEN-dependent modulation in the expression of large groups of genes representing a wide variety of functional categories including genes important in the immune response, cell cycle, transcriptional regulation and cell signaling. A set of genes identified by the microarray analysis was validated by independent real-time PCR analysis. Among upregulated genes were Shrm, Tgfb2, Ube2l6, G1p2, Ccl7 while downregulated genes were Folr1, Tgfbr2, Csrp2, and Dlk1. These results support a versatile function of TFII-I proteins in vertebrate physiology and lead to an increased understanding of the BEN-dependent molecular events.

Gene expression analysis of TFII-I modulated genes in mouse embryonic fibroblasts

TFII-I is a founding member of a family of helix-loop-helix transcription factors involved in modulation of genes through interaction with various nuclear factors and chromatin remodeling complexes. Recent studies indicate that TFII-I performs important function in cell physiology and mouse embryogenesis. In order to understand its molecular role, TFII-I was overexpressed in primary mouse embryonic fibroblasts (MEFs) and alterations in gene expression were monitored with a mouse 16 K oligonucleotide microarray. These studies allowed us to identify genes that lie downstream of TFII-I-dependent pathways. Among the modulated candidates were genes involved in the immunity response, catalytic activity, signaling pathways and transcriptional regulation. Expression of several candidates including those for the interferon-stimulated protein (G1p2), small inducible cytokine A7 (Ccl7), ubiquitin-conjugating enzyme 8 (Ube2l6), cysteine-rich protein (Csrp2) and Drosophila delta-like 1 homolog (Dlk1) were confirmed by real-time PCR. The obtained results suggest that TFII-I participates in multiple signaling and regulatory pathways in MEFs.

Expression of Gtf2ird1, the Williams syndrome-associated gene, during mouse development

The gene GTF2IRD1 is localized within the critical region on chromosome 7 that is deleted in Williams syndrome patients. Genotype-phenotype comparisons of patients carrying variable deletions within this region have implicated GTF2IRD1 and a closely related homolog, GTF2I, as prime candidates for the causation of the principal symptoms of Williams syndrome. We have generated mice with an nls-LacZ knockin mutation of the Gtf2ird1 allele to study its functional role and examine its expression profile. In adults, expression is most prominent in neurons of the central and peripheral nervous system, the retina of the eye, the olfactory epithelium, the spiral ganglion of the cochlea, brown fat adipocytes and to a lesser degree myocytes of the heart and smooth muscle. During development, a dynamic pattern of expression is found predominantly in musculoskeletal tissues, the pituitary, craniofacial tissues, the eyes and tooth buds. Expression of Gtf2ird1 in these tissues correlates with the manifestation of some of the clinical features of Williams syndrome.

Signaling Pathways in Skeletal Muscle Remodeling

Skeletal muscle is comprised of heterogeneous muscle fibers that differ in their physiological and metabolic parameters. It is this diversity that enables different muscle groups to provide a variety of functional properties. In response to environmental demands, skeletal muscle remodels by activating signaling pathways to reprogram gene expression to sustain muscle performance. Studies have been performed using exercise, electrical stimulation, transgenic animal models, disease states, and microgravity to show genetic alterations and transitions of muscle fibers in response to functional demands. Various components of calcium-dependent signaling pathways and multiple transcription factors, coactivators and corepressors have been shown to be involved in skeletal muscle remodeling. Understanding the mechanisms involved in modulating skeletal muscle phenotypes can potentiate the development of new therapeutic measures to ameliorate muscular diseases.

MusTRD can regulate postnatal fiber-specific expression

Human MusTRD1alpha1 was isolated as a result of its ability to bind a critical element within the Troponin I slow upstream enhancer (TnIslow USE) and was predicted to be a regulator of slow fiber-specific genes. To test this hypothesis in vivo, we generated transgenic mice expressing hMusTRD1alpha1 in skeletal muscle. Adult transgenic mice show a complete loss of slow fibers and a concomitant replacement by fast IIA fibers, resulting in postural muscle weakness. However, developmental analysis demonstrates that transgene expression has no impact on embryonic patterning of slow fibers but causes a gradual postnatal slow to fast fiber conversion. This conversion was underpinned by a demonstrable repression of many slow fiber-specific genes, whereas fast fiber-specific gene expression was either unchanged or enhanced. These data are consistent with our initial predictions for hMusTRD1alpha1 and suggest that slow fiber genes contain a specific common regulatory element that can be targeted by MusTRD proteins.

GTF2IRD1 in craniofacial development of humans and mice

Craniofacial abnormalities account for about one-third of all human congenital defects, but our understanding of the genetic mechanisms governing craniofacial development is incomplete. We show that GTF2IRD1 is a genetic determinant of mammalian craniofacial and cognitive development, and we implicate another member of the TFII-I transcription factor family, GTF2I, in both aspects. Gtf2ird1-null mice exhibit phenotypic abnormalities reminiscent of the human microdeletion disorder Williams-Beuren syndrome (WBS); craniofacial imaging reveals abnormalities in both skull and jaws that may arise through misregulation of goosecoid, a downstream target of Gtf2ird1. In humans, a rare WBS individual with an atypical deletion, including GTF2IRD1, shows facial dysmorphism and cognitive deficits that differ from those of classic WBS cases. We propose a mechanism of cumulative dosage effects of duplicated and diverged genes applicable to other human chromosomal disorders.

Multiple GTF2I-like repeats of general transcription factor 3 exhibit DNA binding properties. Evidence for a common origin as a sequence-specific DNA interaction module

A hallmark of general transcription factor 3 (GTF3) is the presence of multiple GTF2I-like repeats that were suggested to mediate protein-protein interactions. However, we have recently demonstrated that repeat 4 is necessary and sufficient for binding of GTF3 to the bicoid-like motif of the Troponin I slow enhancer. Given the sequence similarity between different GTF2I-like repeats we hypothesized that DNA binding might be a common property of this domain type. We subjected five repeats of GTF3 to random oligonucleotide selection (SELEX) to assess their DNA binding potentials. We delineated the consensus sequence G(TC)G(A)GATTA(G)BG(A) for repeat 4 and showed that binding sites for GTF3 in enhancers for Troponin I and homeobox c8 (HOXc8) are in very good agreement with this motif. SELEX selections for repeats 5 and 2 enriched for oligonucleotides that were also bound by R4, suggesting that they share common sequence preferences, whereas repeat 3 exhibited relaxed sequence requirements for DNA binding. No binding was observed for repeat 1. We also show that GTF2I-like repeats 4 and 6 of transcription factor II-I (TFII-I) exhibit modest DNA binding properties. Lastly, we identified several amino acids of GTF3 repeat 4 required for high affinity protein-DNA interaction. Based on the ability of many repeats to bind DNA in vitro, we suggest that GTF2I-like domains evolved by duplication and diversification of a prototypic DNA-binding ancestor.

Adult myogenesis in Drosophila melanogaster can proceed independently of myocyte enhancer factor-2

Myocyte enhancer factor-2 (MEF2) is a transcription factor that is necessary for embryonic muscle development in Drosophila and vertebrates; however, whether this factor is required during later muscle development remains largely unknown. Using heteroallelic combinations of different Mef2 mutant alleles, we isolated and characterized a temperature-sensitive combination. Through temperature-shift experiments, we obtained adult animals that were lacking proper MEF2 function. Many of these individuals died as mature pupae, and those that eclosed showed poor locomotion and an inability to fly. Histological analysis of these animals revealed a requirement for MEF2 in skeletal muscle patterning, although these animals had strikingly normal amounts of muscle tissue. Using quantitative polymerase chain reaction, we determined that expression of the MEF2-regulated actin gene Act57B was severely reduced in these animals. By contrast myofibrillar actin genes unique to the adult stage were only mildly affected. Since MEF2 mutant adults were still capable of forming muscle tissue, we conclude that MEF2 is required for the expression of only a subset of muscle structural genes in the adult. These results indicate that additional muscle-specific factors function to control the myogenesis of complex and diverse muscle in the adult.

Proteomic studies of human and other vertebrate muscle proteins

This review summarizes results of some systemic studies of muscle proteins of humans and some other vertebrates. The studies, started after introduction of two-dimensional gel electrophoresis of O'Farrell, were significantly extended during development of proteomics, a special branch of functional genomics. Special attention is paid to analysis of characteristic features of strategy for practical realization of the systemic approach during three main stages of these studies: pre-genomic, genomic (with organizational registration of proteomics), and post-genomic characterized by active use of structural genomics data. Proteomic technologies play an important role in detection of changes in isoforms of various muscle proteins (myosins, troponins, etc.). These changes possibly reflecting tissue specificity of gene expression may underline functional state of muscle tissues under normal and pathological conditions, and such proteomic analysis is now used in various fields of medicine.

TFII-I, a candidate gene for Williams syndrome cognitive profile: parallels between regional expression in mouse brain and human phenotype

The gene for TFII-I, a widely expressed transcription factor, has been localized to an interval of human chromosome 7q11.23 that is commonly deleted in Williams syndrome (WS). The clinical phenotype of WS includes elfin facies, infantile hypercalcemia, supravalvular aortic stenosis, hyperacusis and mental retardation. The WS cognitive profile (WSCP) is notable for the differential impairment of visual-spatial abilities with relative sparing of verbal-linguistic function. Fine mapping of individuals with WS has revealed a close association between deletion of TFII-I and the WSCP. To determine the plausibility of the hypothesis that hemizygous deletion of TFII-I contributes to the WSCP, we have examined the anatomic distribution of TFII-I RNA and protein isoforms in brains from adult and embryonic mice. Our studies show that early in development, TFII-I expression is widespread and nearly uniform throughout the brain. In adult brain, TFII-I protein is present exclusively in neurons. Highest levels of expression are observed in cerebellar Purkinje cells and in hippocampal interneurons. TFII-I immunoreactivity is distinct from that of the related protein, TFII-IRD1, which is also localized to the region of human chromosome 7 deleted in WS. The expression pattern of TFII-I in mouse brain parallels regions in human brain which have been shown to be anatomically and functionally altered in humans with WS. These observations are consistent with the hypothesis that deletion of the gene for TFII-I contributes to the cognitive impairments observed in WS.

Regulation of Immunoglobulin Promoter Activity by TFII-I Class Transcription Factors

The restriction of immunoglobulin variable region promoter activity to B lymphocytes is a well known paradigm of promoter specificity. Recently, a cis-element, located downstream of the transcription initiation site of murine heavy chain variable promoters, was shown to be critical for B cell activity and specificity. Here we show that mutation of this element, termed DICE (Downstream Immunoglobulin Control Element), reduces in vivo activity in B cells. Gel mobility shift assays show that DICE forms B cell-specific complexes that were also sensitive to DICE mutation. DICE mutation strongly reduces the ability of a distal immunoglobulin heavy chain intronic enhancer to stimulate transcription. We also identify a DICE-interacting factor: a TFII-I-related protein known as BEN (also termed Mus-TRD1 and WBSCR11). Dominant-negative and RNAi-mediated knockdown experiments indicate that BEN can both positively and negatively regulate IgH promoter activity, depending on the cell line.

Innervation-dependent and fiber type-specific transcriptional regulation of the slow myosin heavy chain 2 promoter in avian skeletal muscle fibers

Skeletal muscle fiber type is regulated, in part, by innervation leading to transcriptional regulation of fiber type-specific genes. Here, we report the initial characterization of the transcriptional regulation of the slow myosin heavy chain 2 (MyHC2) promoter in innervated and noninnervated slow medial adductor (MA) and fast pectoralis major (PM) muscle fibers in cell culture. The proximal 1358 bp of slow MyHC2 upstream DNA contains a functional E-box and binding sites for myocyte enhancer factor 2 (MEF2) and nuclear factor of activated T cells (NFAT). Mutagenesis studies indicated that both MEF2 and NFAT binding sites are required for innervation-induced slow MyHC2 promoter activity in MA muscle fibers. However, MEF2 transcription factor activity was unaffected by innervation and did not demonstrate fiber type-specific interactions with the slow MyHC2 MEF2 binding site. NFAT transcription factor activity did increase in innervated MA muscle fibers and not in PM muscle fibers, indicating innervation and muscle fiber type-specific regulation. However, transfection of constitutively active NFAT indicated that NFAT is insufficient to induce slow MyHC2 gene expression in either fast PM or slow MA muscle fibers without innervation. These results indicate the requirement for MEF2 and NFAT in innervation-induced slow MyHC2 gene expression and suggest that additional innervation-dependent and fiber type-specific control of slow MyHC2 gene expression resides in MA and PM muscle fibers, respectively.

Williams-Beuren syndrome: a challenge for genotype-phenotype correlations

Many human chromosomal abnormality syndromes include specific cognitive and behavioural components. Children with Prader-Willi syndrome lack a paternally derived copy of the proximal long arm of chromosome 15, and eat uncontrollably; in Angelman syndrome lack of a maternal contribution of 15q11-q13 results in absence of speech, frequent smiling and episodes of paroxysmal laughter; deletions on 22q11 can be associated with obsessive behaviour and schizophrenia. The neurodevelopmental disorder Williams-Beuren syndrome (WBS), is caused by a microdeletion at 7q11.23 and provides us with one of the most convincing models of a relationship that links genes with human cognition and behaviour. The hypothesis is that deletion of one or a series of genes causes neurodevelopmental abnormalities that manifest as the fractionation of mental abilities typical of WBS. Detailed molecular characterization of the deletion alongside well-defined cognitive profiling in WBS provides a unique opportunity to investigate the neuromolecular basis of complex cognitive behaviour, and develop integrated approaches to study gene function and genotype-phenotype correlations.

hMusTRD1alpha1 represses MEF2 activation of the troponin I slow enhancer

The novel transcription factor hMusTRD1alpha1 (human muscle TFII-I repeat domain-containing protein 1alpha1; previously named MusTRD1; O'Mahoney, J. V., Guven, K. L., Lin, J., Joya, J. E., Robinson, C. S., Wade, R. P., and Hardeman, E. C. (1998) Mol. Cell. Biol. 18, 6641-6652) was identified in a yeast one-hybrid screen as a protein that binds within an upstream enhancer-containing region of the skeletal muscle-specific gene, TNNI1 (human troponin I slow; hTnIslow). It has been proposed that hMusTRD1alpha1 may play an important role in fiber-specific muscle gene expression by virtue of its ability to bind to an Inr-like element (nucleotides -977 to -960) within the hTnIslow upstream enhancer-containing region that is necessary for slow fiber-specific expression. In this study we demonstrate that both MEF2C, a known regulator of slow fiber-specific genes, and hMusTRD1alpha1 regulate hTnIslow through the Inr-like element. Co-transfection assays in C2C12 cells and Cos-7 cells demonstrate that hMusTRD1alpha1 represses hTnIslow transcription and prevents MEF2C-mediated activation of hTnIslow transcription. Gel shift analysis shows that hMusTRD1alpha1 can abrogate MEF2C binding to its cognate site in the hTnIslow enhancer. Glutathione S-transferase pull-down assays demonstrate that hMusTRD1alpha1 can interact with both MEF2C and the nuclear receptor co-repressor. The data support the role of hMusTRD1alpha1 as a repressor of slow fiber-specific transcription through mechanisms involving direct interactions with MEF2C and the nuclear receptor co-repressor.

Regulation of alternative splicing of Gtf2ird1 and its impact on slow muscle promoter activity

A human MusTRD (muscle TFII-I repeat domain (RD)-containing protein) isoform was originally identified in a yeast one-hybrid screen as a protein that binds the slow fibre-specific enhancer of the muscle gene troponin I slow [O'Mahoney, Guven, Lin, Joya, Robinson, Wade and Hardeman (1998) Mol. Cell. Biol. 18, 6641-6652]. MusTRD shares homology with the general transcription factor TFII-I by the presence of diagnostic I-RDs [Roy (2001) Gene 274, 1-13]. The human gene encoding MusTRD, GTF2IRD1 ( WBSCR11 / GTF3 ), was subsequently located on chromosome 7q11.23, a region deleted in the neurodegenerative disease, Williams-Beuren Syndrome [Osborne, Campbell, Daradich, Scherer, Tsui, Franke, Peoples, Francke, Voit, Kramer et al. (1999) Genomics 57, 279-284; Franke, Peoples and Francke (1999) Cytogenet. Cell. Genet. 86, 296-304; Tassabehji, Carette, Wilmot, Donnai, Read and Metcalfe (1999) Eur. J. Hum. Genet. 7, 737-747]. The haploinsufficiency of MusTRD has been implicated in the myopathic aspect of this disease, which manifests itself in symptoms such as lowered resistance to fatigue, kyphoscoliosis, an abnormal gait and joint contractures [Tassabehji, Carette, Wilmot, Donnai, Read and Metcalfe (1999) Eur. J. Hum. Genet. 7, 737-747]. Here, we report the identification of 11 isoforms of MusTRD in mouse skeletal muscles. These isoforms were isolated from a mouse skeletal muscle cDNA library and reverse transcription-PCR on RNA from various adult and embryonic muscles. The variability in these isoforms arises from alternative splicing of a combination of four cassettes and two mutually exclusive exons, all in the 3' region of the primary transcript of Gtf2ird1, the homologous mouse gene. The expression of some of these isoforms is differentially regulated spatially, suggesting individual regulation of the expression of these isoforms. Co-transfection studies in C2C12 muscle cell cultures reveal that isoforms differentially regulate muscle fibre-type-specific promoters. This indicates that the presence of different domains of MusTRD influences the activity exerted by this molecule on multiple promoters active in skeletal muscle.

Molecular regulation of individual skeletal muscle fibre types

The purpose of this review is to present current understanding of cellular and molecular regulation of fibre type expression in skeletal muscle. Published literature seems to conclusively suggest that muscle fibre type expression is regulated by multiple signalling pathways and transcription factors rather than a single 'master' switch or signalling pathway. While the current nomenclature for fibre types is convenient for communication, based upon the evolution of this nomenclature, the prediction that fibre type classifications may change in the future to incorporate post-genomic information is made. It is predicted that future fibre type classifications could be based upon the contractile-activity-induced changes in a common regulatory factor(s) within a subpopulation of genes whose expressions are altered to modify and maintain the new muscle fibre phenotype.

Transcription enhancer factor 1 binds multiple muscle MEF2 and A/T-rich elements during fast-to-slow skeletal muscle fiber type transitions

In adult mouse skeletal muscle, beta-myosin heavy chain (betaMyHC) gene expression is primarily restricted to slow type I fibers; however, its expression can be induced in fast type II fibers in response to a sustained increase in load-bearing work (mechanical overload [MOV]). Our previous betaMyHC transgenic and protein-DNA interaction studies have identified an A/T-rich element (betaA/T-rich -269/-258) that is required for slow muscle expression and which potentiates MOV responsiveness of a 293-bp betaMyHC promoter (beta293wt). Despite the GATA/MEF2-like homology of this element, we found binding of two unknown proteins that were antigenically distinct from GATA and MEF2 isoforms. By using the betaA/T-rich element as bait in a yeast one-hybrid screen of an MOV-plantaris cDNA library, we identified nominal transcription enhancer factor 1 (NTEF-1) as the specific betaA/T-rich binding factor. Electrophoretic mobility shift assay analysis confirmed that NTEF-1 represents the enriched binding activity obtained only when the betaA/T-rich element is reacted with MOV-plantaris nuclear extract. Moreover, we show that TEF proteins bind MEF2 elements located in the control region of a select set of muscle genes. In transient-coexpression assays using mouse C2C12 myotubes, TEF proteins transcriptionally activated a 293-bp betaMyHC promoter devoid of any muscle CAT (MCAT) sites, as well as a minimal thymidine kinase promoter-luciferase reporter gene driven by three tandem copies of the desmin MEF2 or palindromic Mt elements or four tandem betaA/T-rich elements. These novel findings suggest that in addition to exerting a regulatory effect by binding MCAT elements, TEF proteins likely contribute to regulation of skeletal, cardiac, and smooth muscle gene networks by binding select A/T-rich and MEF2 elements under basal and hypertrophic conditions.

Williams syndrome deficits in visual spatial processing linked to GTF2IRD1 and GTF2I on chromosome 7q11.23

PURPOSE

To identify the relationship between specific genes and phenotypic features of Williams syndrome.

METHODS

Subjects were selected based on their deletion status determined by fluorescence in situ hybridization using a panel of 24 BACs and cosmids spanning the region commonly deleted and single gene analysis using Southern blotting. From the cohort of subjects, three had atypical deletions. Physical examinations and cognitive tests were administered to the three subjects and the results were compared to those from a cohort of typical WS subjects.

RESULTS

The molecular results indicate smaller deletions for each subject. In all three cases, typical Williams facies were absent and visual spatial abilities were above that of full deletion WS subjects, particularly in the qualitative aspects of visual spatial processing.

CONCLUSIONS

Combining the molecular analysis with the cognitive results suggest that the genes GTF2IRD1 and GTF2I contribute to deficits on visual spatial functioning.

Characterization of general transcription factor 3, a transcription factor involved in slow muscle-specific gene expression

General transcription factor 3 (GTF3) binds specifically to the bicoid-like motif of the troponin I(slow) upstream enhancer. This motif is part of a sequence that restricts enhancer activity to slow muscle fibers. GTF3 contains multiple helix-loop-helix domains and an amino-terminal leucine zipper motif. Here we show that helix-loop-helix domain 4 is necessary and sufficient for binding the bicoid-like motif. Moreover, the affinity of this interaction is enhanced upon removal of amino-terminal sequences including domains 1 and 2, suggesting that an unmasking of the DNA binding surface may be a precondition for GTF3 to bind DNA in vivo. We have also investigated the interactions of six GTF3 splice variants of the mouse, three of which were identified in this study, with the troponin enhancer. The gamma-isoform lacking exon 23, and exons 26-28 that encode domain 6, interacted most avidly with the bicoid-like motif; the alpha- and beta- isoforms that include these exons fail to bind in gel retardation assays. We also show that GTF3 polypeptides associate with each other via the leucine zipper. We speculate that cells can generate a large number of GTF3 proteins with distinct DNA binding properties by alternative splicing and combinatorial association of GTF3 polypeptides.

Calcineurin signaling and neural control of skeletal muscle fiber type and size

Nerve activity controls muscle contractile function and muscle gene expression. Although excitation-contraction coupling is well characterized, excitation-transcription coupling is still poorly understood. Pharmacological and genetic approaches have been used to dissect the signaling pathways that mediate the effect of nerve activity on muscle fiber type and size. In particular, the role of calcineurin has recently been the subject of intensive investigation and debate. The identification of the transduction pathways involved in neuromuscular signaling has implications for the development of new therapeutic strategies to prevent muscle wasting and loss of muscle power resulting from aging, disuse and neuromuscular disorders.

A fast fiber enhancer exists in the muscle regulatory factor 4 gene promoter

The development of skeletal muscle is a highly regulated process governed by the four myogenic regulatory factors (MRFs) MyoD, myf-5, myogenin, and MRF4. While these factors exhibit some unique functions, part of their individual activity can be attributed to different temporal and spatial expression patterns. To delineate the factors that control expression of the MRFs, we have begun a molecular dissection of the MRF4 gene promoter. Through the generation of promoter/reporter gene constructs, we show that an 853bp fragment, residing 4kb upstream of the MRF4 transcriptional start site (853AV), is able to enhance expression of the basal MRF4 promoter 3-4-fold in myogenic cell cultures. Analysis of the 853AV enhancer in transgenic mice indicates that this region drives MRF4 gene expression primarily in fast muscle fibers, suggesting that the normal adult MRF4 expression pattern is regulated by a variety of control elements that may dictate fiber-type specificity.

The SUMO ubiquitin-protein isopeptide ligase family member Miz1/PIASxbeta /Siz2 is a transcriptional cofactor for TFII-I

We have shown previously that a TFII-I-related protein, hMusTRD1/BEN, represses transcriptional activity of TFII-I. The repression by hMusTRD1/BEN was hypothesized to occur via a two-step competition mechanism involving a cytoplasmic shuttling factor and a nuclear cofactor required for transcriptional activation of TFII-I. Employing a two-hybrid approach with both yeast genomic and mouse cDNA libraries in parallel, we have identified the RING-like zinc finger containing Miz1/PIASxbeta/Siz2, which is a ubiquitin-protein isopeptide ligase in the SUMO pathway, as the potential nuclear cofactor that interacts with both TFII-I and hMusTRD1/BEN. Our conclusion is based on the following observations. First, the interactions are biochemically confirmed in mammalian cells where Miz1/mPIASxbeta interacts with both TFII-I and hMusTRD1/BEN when these proteins are ectopically co-expressed. Second, co-expression of a nuclear localization signal-deficient mutant of Miz1/mPIASxbeta with wild type TFII-I fails to alter the subcellular localization of the former. Finally, ectopically expressed Miz1/mPIASxbeta augments the transcriptional activity of TFII-I and relieves the repression exerted by a mutant hMusTRD1/BEN that co-localized with TFII-I in the nucleus.

Physical and functional interactions of histone deacetylase 3 with TFII-I family proteins and PIASxbeta

TFII-I family proteins are characterized structurally by the presence of multiple reiterated I-repeats, each containing a putative helix-loop-helix domain. Functionally, they behave as multifunctional transcription factors that are activated by a variety of extracellular signals. In studying their subcellular localization, we noticed that these transcription factors frequently reside in subnuclear domains/dots. Because nuclear dots are believed often to harbor components of histone deacetylase enzymes (HDACs), we investigated whether TFII-I family proteins colocalize and interact with HDACs. Here, we show that TFII-I and its related member hMusTRD1/BEN physically and functionally interact with HDAC3. The TFII-I family proteins and HDAC3 also show nearly identical expression patterns in early mouse development. Consistent with our earlier observation that TFII-I family proteins also interact with PIASxbeta, a member of the E3 ligase family involved in the small ubiquitin-like modifier (SUMO) pathway, we show further that PIASxbeta physically and functionally interacts with HDAC3 and relieves the transcriptional repression exerted by HDAC3 upon TFII-I-mediated gene activation. These results suggest a complex interplay between two posttranslational pathways-histone modification and SUMOylation-brokered in part by TFII-I family proteins.

cGMP-dependent protein kinase I beta physically and functionally interacts with the transcriptional regulator TFII-I

Transcriptional regulation of the fos promoter by nitric oxide and cGMP can occur by nuclear translocation of cGMP-dependent protein kinase I (G-kinase I) (Gudi, T., Lohmann, S. M., and Pilz, R. B. (1997) Mol. Cell. Biol. 17, 5244-5254). To identify nuclear targets of G-kinase I, we performed a yeast two-hybrid screen with G-kinase I beta as bait. We found that G-kinase I beta interacted specifically with TFII-I, an unusual transcriptional regulator that associates with multiple proteins to modulate both basal and signal-induced transcription. By using purified recombinant proteins, the interaction was mapped to the N-terminal 93 amino acids of G-kinase I beta and one of six 95-amino acid repeats found in TFII-I. In baby hamster kidney cells, cGMP analogs enhanced co-immunoprecipitation of G-kinase I beta and TFII-I by inducing co-localization of both proteins in the nucleus, but in other cell types containing cytoplasmic TFII-I the G-kinase-TFII-I interaction was largely cGMP-independent. G-kinase phosphorylated TFII-I in vitro and in vivo on Ser(371) and Ser(743) outside of the interaction domain. G-kinase strongly enhanced TFII-I transactivation of a serum-response element-containing promoter in COS7 cells, and this effect was lost when Ser(371) and Ser(743) of TFII-I were mutated. TFII-I by itself had little effect on a full-length fos promoter in baby hamster kidney cells, but it synergistically enhanced transcriptional activation by G-kinase I beta. Binding of G-kinase to TFII-I may position the kinase to phosphorylate and regulate TFII-I and/or factors that interact with TFII-I at the serum-response element.

Phenotypic adaptations in human muscle fibers 6 and 24 wk after spinal cord injury

The effects of spinal cord injury (SCI) on the profile of sarco(endo) plasmic reticulum calcium-ATPase (SERCA) and myosin heavy chain (MHC) isoforms in individual vastus lateralis (VL) muscle fibers were determined. Biopsies from the VL were obtained from SCI subjects 6 and 24 wk postinjury (n = 6). Biopsies from nondisabled (ND) subjects were obtained at two time points 18 wk apart (n = 4). In ND subjects, the proportions of VL fibers containing MHC I, MHC IIa, and MHC IIx were 46 +/- 3, 53 +/- 3, and 1 +/- 1%, respectively. Most MHC I fibers contained SERCA2. Most MHC IIa fibers contained SERCA1. All MHC IIx fibers contained SERCA1 exclusively. SCI resulted in significant increases in fibers with MHC IIx (14 +/- 4% at 6 wk and 16 +/- 2% at 24 wk). In addition, SCI resulted in high proportions of MHC I and MHC IIa fibers with both SERCA isoforms (29% at 6 wk and 54% at 24 wk for MHC I fibers and 16% at 6 wk and 38% at 24 wk for MHC IIa fibers). Thus high proportions of VL fibers were mismatched for SERCA and MHC isoforms after SCI (19 +/- 3% at 6 wk and 36 +/- 9% at 24 wk) compared with only ~5% in ND subjects. These data suggest that, in the early time period following SCI, fast fiber isoforms of both SERCA and MHC are elevated disproportionately, resulting in fibers that are mismatched for SERCA and MHC isoforms. Thus the adaptations in SERCA and MHC isoforms appear to occur independently.

Genomic organization of the genes Gtf2ird1, Gtf2i, and Ncf1 at the mouse chromosome 5 region syntenic to the human chromosome 7q11.23 Williams syndrome critical region

We have recently isolated a mouse ortholog of human GTF2IRD1 that is related to GTF2I. GTF2IRD1 and GTF2I proteins are characterized by the presence of multiple helix-loop-helix domains and a leucine zipper motif. Both paralogs are closely linked and deleted hemizygously in individuals with Williams syndrome, a dominant genetic condition characterized by unique neurocognitive and behavioral features. We have isolated and analyzed the sequence of bacterial artificial chromosome clones from the syntenic mouse chromosome 5 region that contains Gtf2ird1 and Gtf2i as well as a neighboring gene, Ncf1. Gtf2ird1 is composed of 31 exons spanning >100 kb on mouse chromosome 5 and is located between Cyln2 and Gtf2i. Gtf2i is composed of 34 exons spanning about 77 kb. Ncf1, located downstream of Gtf2i, consists of 11 exons that extend over 8 kb. The gene organization of Gtf2ird1, Gtf2i, and Ncf1 is conserved in mice and humans, although the intronic regions are more compact in the mouse genome. The helix-loop-helix repeats of Gtf2ird1 and Gtf2i are encoded separately on adjacent exons and were generated by independent genomic rearrangements. These studies contribute to our knowledge of transcription factor defects and their pathogenesis in haploinsufficiency conditions.

Coregulation of fast contractile protein transgene and glycolytic enzyme expression in mouse skeletal muscle

Little is known of the gene regulatory mechanisms that coordinate the contractile and metabolic specializations of skeletal muscle fibers. Here we report a novel connection between fast isoform contractile protein transgene and glycolytic enzyme expression. In quantitative histochemical studies of transgenic mouse muscle fibers, we found extensive coregulation of the glycolytic enzyme glycerol-3-phosphate dehydrogenase (GPDH) and transgene constructs based on the fast skeletal muscle troponin I (TnIfast) gene. In addition to a common IIB > IIX > IIA fiber type pattern, TnIfast transgenes and GPDH showed correlated fiber-to-fiber variation within each fast fiber type, concerted emergence of high-level expression during early postnatal muscle maturation, and parallel responses to muscle under- or overloading. Regulatory information for GPDH-coregulated expression is carried by the TnIfast first-intron enhancer (IRE). These results identify an unexpected contractile/metabolic gene regulatory link that is amenable to further molecular characterization. They also raise the possibility that the equal expression in all fast fiber types observed for the endogenous TnIfast gene may be driven by different metabolically coordinated mechanisms in glycolytic (IIB) vs. oxidative (IIA) fast fibers.

Molecular dissection of DNA sequences and factors involved in slow muscle-specific transcription

Transcription is a major regulatory mechanism for the generation of slow- and fast-twitch myofibers. We previously identified an upstream region of the slow TnI gene (slow upstream regulatory element [SURE]) and an intronic region of the fast TnI gene (fast intronic regulatory element [FIRE]) that are sufficient to direct fiber type-specific transcription in transgenic mice. Here we demonstrate that the downstream half of TnI SURE, containing E box, NFAT, MEF-2, and CACC motifs, is sufficient to confer pan-skeletal muscle-specific expression in transgenic mice. However, upstream regions of SURE and FIRE are required for slow and fast fiber type specificity, respectively. By adding back upstream SURE sequences to the pan-muscle-specific enhancer, we delineated a 15-bp region necessary for slow muscle specificity. Using this sequence in a yeast one-hybrid screen, we isolated cDNAs for general transcription factor 3 (GTF3)/muscle TFII-I repeat domain-containing protein 1 (MusTRD1). GTF3 is a multidomain nuclear protein related to initiator element-binding transcription factor TF II-I; the genes for both proteins are deleted in persons with Williams-Beuren syndrome, who often manifest muscle weakness. Gel retardation assays revealed that full-length GTF3, as well as its carboxy-terminal half, specifically bind the bicoid-like motif of SURE (GTTAATCCG). GTF3 expression is neither muscle nor fiber type specific. Its levels are highest during a period of fetal development that coincides with the emergence of specific fiber types and transiently increases in regenerating muscles damaged by bupivacaine. We further show that transcription from TnI SURE is repressed by GTF3 when overexpressed in electroporated adult soleus muscles. These results suggest a role for GTF3 as a regulator of slow TnI expression during early stages of muscle development and suggest how it could contribute to Williams-Beuren syndrome.

Activation of MEF2 by muscle activity is mediated through a calcineurin-dependent pathway

Gene expression in skeletal muscles of adult vertebrates is altered profoundly by changing patterns of contractile work. Here we observed that the functional activity of MEF2 transcription factors is stimulated by sustained periods of endurance exercise or motor nerve pacing, as assessed by expression in trans genic mice of a MEF2-dependent reporter gene (desMEF2-lacZ). This response is accompanied by transformation of specialized myofiber subtypes, and is blocked either by cyclosporin A, a specific chemical inhibitor of calcineurin, or by forced expression of the endogenous calcineurin inhibitory protein, myocyte-enriched calcineurin interacting protein 1. Calcineurin removes phosphate groups from MEF2, and augments the potency of the transcriptional activation domain of MEF2 fused to a heterologous DNA binding domain. Across a broad range, the enzymatic activity of calcineurin correlates directly with expression of endogenous genes that are transcriptionally activated by muscle contractions. These results delineate a molecular pathway in which calcineurin and MEF2 participate in the adaptive mechanisms by which skeletal myofibers acquire specialized contractile and metabolic properties as a function of changing patterns of muscle contraction.

Regulation of myosin heavy chain expression during rat skeletal muscle development in vitro

Signals that determine fast- and slow-twitch phenotypes of skeletal muscle fibers are thought to stem from depolarization, with concomitant contraction and activation of calcium-dependent pathways. We examined the roles of contraction and activation of calcineurin (CN) in regulation of slow and fast myosin heavy chain (MHC) protein expression during muscle fiber formation in vitro. Myotubes formed from embryonic day 21 rat myoblasts contracted spontaneously, and approximately 10% expressed slow MHC after 12 d in culture, as seen by immunofluorescent staining. Transfection with a constitutively active form of calcineurin (CN*) increased slow MHC by 2.5-fold as determined by Western blot. This effect was attenuated 35% by treatment with tetrodotoxin and 90% by administration of the selective inhibitor of CN, cyclosporin A. Conversely, cyclosporin A alone increased fast MHC by twofold. Cotransfection with VIVIT, a peptide that selectively inhibits calcineurin-induced activation of the nuclear factor of activated T-cells, blocked the effect of CN* on slow MHC by 70% but had no effect on fast MHC. The results suggest that contractile activity-dependent expression of slow MHC is mediated largely through the CN-nuclear factor of activated T-cells pathway, whereas suppression of fast MHC expression may be independent of nuclear factor of activated T-cells.