@article {2385, title = {Subnuclear segregation of genes and core promoter factors in myogenesis. (With commentary)}, journal = {Genes \& Development}, volume = {25}, year = {2011}, month = {2011 Mar 15}, pages = {569-80}, abstract = {

Recent findings implicate alternate core promoter recognition complexes in regulating cellular differentiation. Here we report a spatial segregation of the alternative core factor TAF3, but not canonical TFIID subunits, away from the nuclear periphery, where the key myogenic gene MyoD is preferentially localized in myoblasts. This segregation is correlated with the differential occupancy of TAF3 versus TFIID at the MyoD promoter. Loss of this segregation by modulating either the intranuclear location of the MyoD gene or TAF3 protein leads to altered TAF3 occupancy at the MyoD promoter. Intriguingly, in differentiated myotubes, the MyoD gene is repositioned to the nuclear interior, where TAF3 resides. The specific high-affinity recognition of H3K4Me3 by the TAF3 PHD (plant homeodomain) finger appears to be required for the sequestration of TAF3 to the nuclear interior. We suggest that intranuclear sequestration of core transcription components and their target genes provides an additional mechanism for promoter selectivity during differentiation.

Commentary: Jie Yao in Bob Tijan{\textquoteright}s lab used a combination of confocal microscopy and dual label PALM in thin sections cut from resin-embedded cells to show that certain core transcription components and their target genes are spatially segregated in myoblasts, but not in differentiated myotubes, suggesting that such spatial segregation may play a role in guiding cellular differentiation.

}, issn = {1549-5477}, doi = {10.1073/pnas.1100640108}, author = {Yao, Jie and Fetter, Richard D and Hu, Ping and Betzig, Eric and Tjian, Robert} } @article {2392, title = {Codependent activators direct myoblast-specific MyoD transcription.}, journal = {Developmental Cell}, volume = {15}, year = {2008}, month = {2008 Oct}, pages = {534-46}, abstract = {

Although FoxO and Pax proteins represent two important families of transcription factors in determining cell fate, they had not been functionally or physically linked together in mediating regulation of a common target gene during normal cellular transcription programs. Here, we identify MyoD, a key regulator of myogenesis, as a direct target of FoxO3 and Pax3/7 in myoblasts. Our cell-based assays and in vitro studies reveal a tight codependent partnership between FoxO3 and Pax3/7 to coordinately recruit RNA polymerase II and form a preinitiation complex (PIC) to activate MyoD transcription in myoblasts. The role of FoxO3 in regulating muscle differentiation is confirmed in vivo by observed defects in muscle regeneration caused by MyoD downregulation in FoxO3 null mice. These data establish a mutual interdependence and functional link between two families of transcription activators serving as potential signaling sensors and regulators of cell fate commitment in directing tissue specific MyoD transcription.

}, keywords = {Animals, Cell Line, Forkhead Transcription Factors, Genetic, Immunohistochemistry, Knockout, Mice, Myoblasts, MyoD Protein, Paired Box Transcription Factors, RNA, RNA Interference, Small Interfering, Trans-Activators, Transcription, Transfection}, issn = {1878-1551}, doi = {10.1073/pnas.1100640108}, author = {Hu, Ping and Geles, Kenneth G and Paik, Ji-Hye and DePinho, Ronald A and Tjian, Robert} } @article {2396, title = {ES cell pluripotency and germ-layer formation require the SWI/SNF chromatin remodeling component BAF250a.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {105}, year = {2008}, month = {2008 May 6}, pages = {6656-61}, abstract = {

ATP-dependent chromatin remodeling complexes are a notable group of epigenetic modifiers that use the energy of ATP hydrolysis to change the structure of chromatin, thereby altering its accessibility to nuclear factors. BAF250a (ARID1a) is a unique and defining subunit of the BAF chromatin remodeling complex with the potential to facilitate chromosome alterations critical during development. Our studies show that ablation of BAF250a in early mouse embryos results in developmental arrest (about embryonic day 6.5) and absence of the mesodermal layer, indicating its critical role in early germ-layer formation. Moreover, BAF250a deficiency compromises ES cell pluripotency, severely inhibits self-renewal, and promotes differentiation into primitive endoderm-like cells under normal feeder-free culture conditions. Interestingly, this phenotype can be partially rescued by the presence of embryonic fibroblast cells. DNA microarray, immunostaining, and RNA analyses revealed that BAF250a-mediated chromatin remodeling contributes to the proper expression of numerous genes involved in ES cell self-renewal, including Sox2, Utf1, and Oct4. Furthermore, the pluripotency defects in BAF250a mutant ES cells appear to be cell lineage-specific. For example, embryoid body-based analyses demonstrated that BAF250a-ablated stem cells are defective in differentiating into fully functional mesoderm-derived cardiomyocytes and adipocytes but are capable of differentiating into ectoderm-derived neurons. Our results suggest that BAF250a is a key component of the gene regulatory machinery in ES cells controlling self-renewal, differentiation, and cell lineage decisions.

}, keywords = {Adipocytes, Animals, Cardiac, Cell Differentiation, Cell Line, Cell Lineage, Cell Proliferation, Chromatin Assembly and Disassembly, Chromosomal Proteins, Developmental, DNA-Binding Proteins, Embryo, Embryonic Development, Embryonic Stem Cells, Female, Genes, Germ Layers, Knockout, Male, Mammalian, Mice, Muscle, Myocytes, Non-Histone, Nuclear Proteins, Pluripotent Stem Cells, Skeletal, Transcription Factors}, issn = {1091-6490}, doi = {10.1073/pnas.1100640108}, author = {Gao, Xiaolin and Tate, Peri and Hu, Ping and Tjian, Robert and Skarnes, William C and Wang, Zhong} } @article {2393, title = {MyoD targets TAF3/TRF3 to activate myogenin transcription.}, journal = {Molecular Cell}, volume = {32}, year = {2008}, month = {2008 Oct 10}, pages = {96-105}, abstract = {

Skeletal muscle differentiation requires a cascade of transcriptional events to control the spatial and temporal expression of muscle-specific genes. Until recently, muscle-specific transcription was primarily attributed to prototypic enhancer-binding factors, while the role of core promoter recognition complexes in directing myogenesis remained unknown. Here, we report the development of a purified reconstituted system to analyze the properties of a TAF3/TRF3 complex in directing transcription initiation at the Myogenin promoter. Importantly, this new complex is required to replace the canonical TFIID to recapitulate MyoD-dependent activation of Myogenin. In vitro and cell-based assays identify a domain of TAF3 that mediates coactivator functions targeted by MyoD. Our findings also suggest changes to CRSP/Mediator in terminally differentiated myotubes. This switching of the core promoter recognition complex during myogenesis allows a more balanced division of labor between activators and TAF coactivators, thus providing another strategy to accommodate cell-specific regulation during metazoan development.

}, keywords = {Animals, Cell Line, Genetic, Homeodomain Proteins, Mice, Multiprotein Complexes, Muscle Fibers, MyoD Protein, Myogenin, Promoter Regions, Protein Structure, Protein Subunits, Recombinant Proteins, Skeletal, TATA Box Binding Protein-Like Proteins, Tertiary, Trans-Activators, Transcription Factor TFIID, Transcription Initiation Site, Transcriptional Activation}, issn = {1097-4164}, doi = {10.1073/pnas.1100640108}, author = {Deato, Maria Divina E and Marr, Michael T and Sottero, Theo and Inouye, Carla and Hu, Ping and Tjian, Robert} }