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Substantial evidence supports the hypothesis that enhancers are critical regulators of cell-type determination, orchestrating both positive and negative transcriptional programs; however, the basic mechanisms by which enhancers orchestrate interactions with cognate promoters during activation and repression events remain incompletely understood. Here we report the required actions of LIM domain-binding protein 1 (LDB1)/cofactor of LIM homeodomain protein 2/nuclear LIM interactor, interacting with the enhancer-binding protein achaete-scute complex homolog 1, to mediate looping to target gene promoters and target gene regulation in corticotrope cells. LDB1-mediated enhancer:promoter looping appears to be required for both activation and repression of these target genes. Although LDB1-dependent activated genes are regulated at the level of transcriptional initiation, the LDB1-dependent repressed transcription units appear to be regulated primarily at the level of promoter pausing, with LDB1 regulating recruitment of metastasis-associated 1 family, member 2, a component of the nucleosome remodeling deacetylase complex, on these negative enhancers, required for the repressive enhancer function. These results indicate that LDB1-dependent looping events can deliver repressive cargo to cognate promoters to mediate promoter pausing events in a pituitary cell type.

Enhancers provide critical information directing cell-type-specific transcriptional programs, regulated by binding of signal-dependent transcription factors and their associated cofactors. Here, we report that the most strongly activated estrogen (E2)-responsive enhancers are characterized by trans-recruitment and in situ assembly of a large 1-2 MDa complex of diverse DNA-binding transcription factors by ERα at ERE-containing enhancers. We refer to enhancers recruiting these factors as mega transcription factor-bound in trans (MegaTrans) enhancers. The MegaTrans complex is a signature of the most potent functional enhancers and is required for activation of enhancer RNA transcription and recruitment of coactivators, including p300 and Med1. The MegaTrans complex functions, in part, by recruiting specific enzymatic machinery, exemplified by DNA-dependent protein kinase. Thus, MegaTrans-containing enhancers represent a cohort of functional enhancers that mediate a broad and important transcriptional program and provide a molecular explanation for transcription factor clustering and hotspots noted in the genome.

Author(s): Jianxun Wang [1, 2]; Kathleen Scully [1, 6]; Xiaoyan Zhu [1, 6]; Ling Cai [1, 3, 6]; Jie Zhang [1]; Gratien G. Prefontaine [1]; Anna Krones [1]; Kenneth A. [...]

An unexpected strategy for [beta]-catenin-dependent regulation of cell-lineage determination based on interactions between [beta]-catenin and a specific homeodomain factor, Prop1, is presented. A novel transcriptional strategy that underlies [beta]-catenin control of cell-lineage determination in organogenesis is discovered during the study.

Author(s): Xue Li (corresponding author) [1]; Kenneth A. Ohgi [1]; Jie Zhang [1]; Anna Krones [1]; Kevin T. Bush [2]; Christopher K. Glass [3]; Sanjay K. Nigam [2]; Aneel K. [...]

Results demonstrate the molecular basis for the exchange of coactivators for corepressors during development and homeostasis in murine cells is the discrimination by the nuclear receptor AF2 motif of the coactivator and corepressor interacting helices.

LXXLL-containing motifs may have evolved to permit both receptor-specific and ligand-specific assembly of a coactivator complex. Ligand-dependent activation of gene transcription requires co-activators. The thyroid hormone cannot be activated without the combined participation of two helical domains, and research suggests the core LXXLL motif makes differential contacts with helices 1 and 3 in receptor ligand-binding remains.

A family of p160 coactivators was initially identified based on ligand-dependent interactions with nuclear receptors and thought to function, in part, by recruiting CREB-binding protein/ p300 to several classes of transcription factors. One of the p160 factors, p/CIP/AIB1, often amplified and overexpressed in breast cancer, also exhibits particularly strong interaction with CREB-binding protein/p300. In this manuscript, we report that p/CIP, which exhibits regulated transfer from cytoplasm to nucleus, is required for normal somatic growth from embryonic day 13.5 through maturity. Our data suggest that a short stature phenotype of p/CIP gene-deleted mice reflect both altered regulation of insulin-like growth factor-1 (IGF-1) gene expression in specific tissues and a cell-autonomous defect of response to IGF-1, including ineffective transcriptional activities by several classes of regulated transcription factors under specific conditions. The actions of p/CIP are therefore required for full expression of a subset of genes critical for regulating physiological patterns of somatic growth in mammals.

Substantial evidence supports the hypothesis that enhancers are critical regulators of cell-type determination, orchestrating both positive and negative transcriptional programs; however, the basic mechanisms by which enhancers orchestrate interactions with cognate promoters during activation and repression events remain incompletely understood. Here we report the required actions of LIM domain-binding protein 1 (LDB1)/cofactor of LIM homeodomain protein 2/nuclear LIMinteractor, interactingwith the enhancer-binding protein achaete-scute complex homolog 1, to mediate looping to target gene promoters and target gene regulation in corticotrope cells. LDB1-mediated enhancer:promoter looping appears to be required for both activation and repression of these target genes. Although LDB1-dependent activated genes are regulated at the level of transcriptional initiation, the LDB1-dependent repressed transcription units appear to be regulated primarily at the level of promoter pausing, with LDB1 regulating recruitment of metastasis-associated 1 family, member 2, a component of the nucleosome remodeling deacetylase complex, on these negative enhancers, required for the repressive enhancer function. These results indicate that LDB1-dependent looping events can deliver repressive cargo to cognate promoters to mediate promoter pausing events in a pituitary cell type. [ABSTRACT FROM AUTHOR]

Author(s): Xue Li; Kenneth A. Ohgi; Jie Zhang; Anna Krones; Kevin T. Bush; Christopher K. Glass; Sanjay K. Nigam; Aneel K. Aggarwal; Richard Maas; David W. Rose; Michael G. Rosenfeld [...]

Enhancers have been functionally described for >35 years, but the molecular principles underlying the integration of regulatory inputs to alternate gene enhancers used during mammalian organogenesis remain incompletely understood. Using a combination of in vivo enhancer mapping and proteomics approaches, we have established that two distant and distinct early enhancers, each requiring different transcription complexes, are required for full activation of the gene encoding the pituitary lineage determining factor, Pit1. A transcription factor belonging to the "giant, multiple-homeodomain and zinc finger family." Atbf1, serves as a novel pituitary regulator for one of the two required enhancers as shown by genetic and in vitro analysis. Enhancers have been functionally described for >35 years, but the molecular principles underlying the integration of regulatory inputs to alternate gene enhancers used during mammalian organogenesis remain incompletely understood. Using a combination of in vivo enhancer mapping and proteomics approaches, we have established that two distant and distinct early enhancers, each requiring different transcription complexes, are required for full activation of the gene encoding the pituitary lineage determining factor, Pit1. A transcription factor belonging to the "giant, multiple-homeodomain and zinc finger family." Atbf1, serves as a novel pituitary regulator for one of the two required enhancers as shown by genetic and in vitro analysis. [ABSTRACT FROM AUTHOR]

The precise mechanistic relationship between gene activation and repression events is a central question in mammalian organogenesis, as exemplified by the evolutionarily conserved sine oculis (Six), eyes absent (Eya) and dachshund (Dach) network of genetically interacting proteins. Here, we report that Six1 is required for the development of murine kidney, muscle and inner ear, and that it exhibits synergistic genetic interactions with Eya factors. We demonstrate that the Eya family has a protein phosphatase function, and that its enzymatic activity is required for regulating genes encoding growth control and signalling molecules, modulating precursor cell proliferation. The phosphatase function of Eya switches the function of Six1-Dach from repression to activation, causing transcriptional activation through recruitment of co-activators. The gene-specific recruitment of a co-activator with intrinsic phosphatase activity provides a molecular mechanism for activation of specific gene targets, including those regulating precursor cell proliferation and survival in mammalian organogenesis. [ABSTRACT FROM AUTHOR]

Presents a correction to the article "Eya Protein Phosphatase Activity Regulates Six1-Dach-Eya Transcriptional Effects in Mammalian Organogenesis," that was previously published in the 2003 issue of the periodical "Nature."

Investigates the defect in the histone acetyltransferase activity of the nuclear transcriptional coactivator CREB-binding protein (CBP) in Rubinstein-Taybi syndrome (RTS). Identification of microdeletion in one RTS patient using fluorescent in situ hybridization analysis; Heteroallelic mutations; Introduction of missense mutation to recombinant mouse CBP.