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Contrasting and brain region-specific roles of neurogenin2 and mash1 in GABAergic neuron differentiation in vitro

EXPERIMENTAL CELL RESEARCH 2007年第19期313卷 4066-4081页

作者： Jo, A-Young Park, Chang-Hwan Aizawa, Shinichi Lee, Sang-Hun Hanyang Univ Coll Med Dept Biochem & Mol Biol Seoul 133791 South Korea Hanyang Univ Coll Med Dept Microbiol Seoul 133791 South Korea Hanyang Univ Dept Inst Mental Hlth Seoul 133791 South Korea Hanyang Univ Dept Cell Therapy Res Ctr Seoul 133791 South Korea RIKEN CDB Vertebrate Body Plan Grp Chuou Ku Kobe Hyogo 6500047 Japan

We have cultivated highly uniform populations of neural precursor cells, which retain their region-specific identities, from various rat embryonic brain regions. The roles of the proneural basic-helix-loop-helix (bHLH) factors neurogenin2 (Ngn2) and Mash1 in gamma-aminobutyric acid (GABA) neuron differentiation were explored in the region-specific cultures. Consistent with previous in vivo studies, forced expression of Mash1 promoted GABA neuron formation from the precursors derived from the developing forebrains, whereas Ngn2 displayed an inhibitory role in forebrain GABA neuron differentiation. Functional analyses of mutant bHLH proteins indicated that the helix-loop-helix domains of Mash1 and Ngn2, known as the structures for protein-protein interactions, impart the distinct activities. Intriguingly, the regulatory activities of Mash1 and Ngn2 in GABA neuron differentiation from the hindbrain- and spinal cord-derived precursor cells were completely opposite of those observed in the forebrain- derived cultures: increased GABA neuron yield by Ngn2 and decreased yield by Mash1 were shown in the precursors of those posterior brain regions. No clear difference that depended on dorsal-ventral brain regions was observed in the bHLH-mediated activities. Finally, we demonstrated that Otx2, the expression of which is developmentally confined to the regions anterior to the isthmus, is a factor responsible for the anterior-posterior region-dependent opposite effects of the bHLH proteins. (C) 2007 Elsevier Inc. All rights reserved.

关键词： gamma-aminobutyric acid neuron basic helix-loop-helix neurogenin2 mash1

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Iron assimilation and transcription factor controlled synthesis of riboflavin in plants

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PLANTA 2007年第1期226卷 147-158页

作者： Vorwieger, A. Gryczka, C. Czihal, A. Douchkov, D. Tiedemann, J. Mock, H.-P. Jakoby, M. Weisshaar, B. Saalbach, I. Baumlein, H. Inst Plant Genet & Crop Plant Res D-06466 Gatersleben Germany Univ Cologne Lehrstuhl Bot 3 Cologne Germany Univ Bielefeld Lehrstuhl Genomforsch D-4800 Bielefeld Germany

Iron homeostasis is vital for many cellular processes and requires a precise regulation. Several iron efficient plants respond to iron starvation with the excretion of riboflavin and other flavins. basic helix-loop-helix transcription factors (TF) are involved in the regulation of many developmental processes, including iron assimilation. Here we describe the isolation and characterisation of two Arabidopsis bHLH TF genes, which are strongly induced under iron starvation. Their heterologous ectopic expression causes constitutive, iron starvation independent excretion of riboflavin. The results show that both bHLH TFs represent an essential component of the regulatory pathway connecting iron deficiency perception and riboflavin excretion and might act as integrators of various stress reactions.

关键词： basic helix-loop-helix iron assimilation riboflavin transcription factor

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Delta-Notch-and then? Protein interactions and proposed modes of repression by Hes and Hey bHLH factors

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NUCLEIC ACIDS RESEARCH 2007年第14期35卷 4583-4596页

作者： Fischer, Andreas Gessler, Manfred Univ Wurzburg Bioctr Theodor Boveri Inst D-97074 Wurzburg Germany

Hes and Hey genes are the mammalian counterparts of the Hairy and Enhancer-of-split type of genes in Drosophila and they represent the primary targets of the Delta-Notch signaling pathway. Hairy-related factors control multiple steps of embryonic development and misregulation is associated with various defects. Hes and Hey genes (also called Hesr, Chf, Hrt, Herp or gridlock) encode transcriptional regulators of the basic helix-loop-helix class that mainly act as repressors. The molecular details of how Hes and Hey proteins control transcription are still poorly understood, however. Proposed modes of action include direct binding to N- or E-box DNA sequences of target promoters as well as indirect binding through other sequence-specific transcription factors or sequestration of transcriptional activators. Repression may rely on recruitment of corepressors and induction of histone modifications, or even interference with the general transcriptional machinery. All of these models require extensive protein - protein interactions. Here we review data published on protein - protein and protein - DNA interactions of Hairy-related factors and discuss their implications for transcriptional regulation. In addition, we summarize recent progress on the identification of potential target genes and the analysis of mouse models.

关键词： .recruitment corepressors basic helix-loop-helix Hey genes Hey proteins

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The E-protein Tcf4 interacts with Math1 to regulate differentiation of a specific subset of neuronal progenitors

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PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 2007年第39期104卷 15382-15387页

作者： Flora, Adriano Garcia, Jesus J. Thaller, Christina Zoghbi, Huda Y. Baylor Coll Med Howard Hughes Med Inst Houston TX 77030 USA Baylor Coll Med Dept Human Mol Genet Houston TX 77030 USA Baylor Coll Med Dept Biochem & Mol Biol Houston TX 77030 USA Baylor Coll Med Dept Neurosci Houston TX 77030 USA Baylor Coll Med Dept Pediat Houston TX 77030 USA Baylor Coll Med Program Dev Biol Houston TX 77030 USA

Proneural factors represent < 10 transcriptional regulators required for specifying all of the different neurons of the mammalian nervous system. The mechanisms by which such a small number of factors creates this diversity are still unknown. We propose that proteins interacting with proneural factors confer such specificity. To test this hypothesis we isolated proteins that interact with Math1, a proneural transcription factor essential for the establishment of a neural progenitor population (rhombic lip) that gives rise to multiple hindbrain structures and identified the E-protein Tcf4. Interestingly, haploin-sufficiency of TCF4 causes the Pitt-Hopkins mental retardation syndrome, underscoring the important role for this protein in neural development. To investigate the functional relevance of the Math1/ Tcf4 interaction in vivo, we studied Tcf4(-/-) mice and found that they have disrupted pontine nucleus development. Surprisingly, this selective deficit occurs without affecting other rhornbic lip-derived nuclei, despite expression of Math1 and Tcf4 throughout the rhombic lip. Importantly, deletion of any of the other E-protein-encoding genes does not have detectable effects on Math1-dependent neurons, suggesting a specialized role for Tcf4 in distinct neural progenitors. Our findings provide the first in vivo evidence for an exclusive function of dimers formed between a proneural basic helix-loop-helix factor and a specific E-protein, offering insight about the mechanisms underlying transcriptional programs that regulate development of the mammalian nervous system.

关键词： basic helix-loop-helix mental retardation neural development proneural

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Developmentally regulated synthesis of p8, a stress-associated transcription cofactor, in diapause-destined embryos of Artemia franciscana

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CELL STRESS & CHAPERONES 2007年第3期12卷 255-264页

作者： Qiu, Zhijun MacRae, Thomas H. Dalhousie Univ Dept Biol Halifax NS B3H 4J1 Canada

Diapause-destined embryos of the crustacean Artemia franciscana arrest as gastrulae, acquire extreme stress tolerance, and enter profound metabolic dormancy. Among genes upregulated at 2 days postfertilization in these embryos is a homologue of p8, a stress-inducible transcription cofactor. Artemia p8 is smaller than vertebrate homologues but shares a basic helix-loop-helix domain and a bipartite nuclear localization signal. Probing of restriction digested DNA on Southern blots indicated a single Artemia p8 gene and 5'-RACE specified 2 transcription start sites. Several putative cis-acting regulatory sequences, including two heat shock elements, appeared upstream of the p8 transcription start-site. Artemia p8 mRNA increased sharply at 1 day postfertilization in diapause-destined embryos and then declined, whereas p8 protein appeared 2 days postfertilization and remained relatively constant throughout development, indicating a stable protein. p8 was not detectable in nauplius-destined (nondiapause) Artemia embryos. Immunofluorescent staining revealed p8 within Artemia nuclei., The results support the idea that p8, a known stress-responsive transcription cofactor, mediates gene expression in diapause-destined Artemia embryos. p8 is the first diapause-related transcription factor identified in crustaceans and 11 of only a small number of such proteins identified in any organism undergoing diapause.

关键词： .upregulated digested nuclear localization blots cis-acting basic helix-loop-helix transcription start postfertilization franciscana Artemia Embryos transcription cofactor embryos of Artemia Artemia gene

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Iron deficiency-mediated stress regulation of four subgroup Ib BHLH genes in Arabidopsis thaliana

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PLANTA 2007年第4期226卷 897-908页

作者： Wang, Hong-Yu Klatte, Marco Jakoby, Marc Baeumlein, Helmut Weisshaar, Bernd Bauer, Petra Univ Saarland Dept Biosci Bot D-66041 Saarbrucken Germany Max Planck Inst Breeding Res D-50829 Cologne Germany Inst Plant Genet & Crop Plant Res IPK D-06466 Gatersleben Germany Univ Bielefeld Fac Biol D-33594 Bielefeld Germany

Networks of transcription factors control physiological, developmental and environmental responses. Root iron acquisition responses are controlled by the essential bHLH protein FIT. Recently, two group Ib BHLH genes were reported to be iron deficiency-regulated. Here, we studied expression patterns of these two group Ib BHLH genes and of their two closest homologs to analyze whether their regulation would support a function in iron deficiency responses. We found that BHLH038, BHLH039, BHLH100 and BHLH101 (comprising a subgroup of BHLH Ib genes) were up regulated by iron deficiency in roots and leaves. Single insertion mutants had no visible phenotype and were capable of inducing root iron acquisition responses, presumably due to functional redundancy. Specific metal treatments like nickel, high zinc or high copper resulted in induction of the four BHLH Ib genes whereas high iron, low copper and low zinc repressed gene expression. Induction of the four BHLH Ib genes was also found in multiple iron acquisition mutants including fit. Ectopic activation of FIT did not suppress the four BHLH Ib genes. Split-root analyses using promoter-GUS lines showed that FIT and BHLH100 promoters were controlled by different local and systemic signals involved in their regulation by iron. These results indicated that the four BHLH Ib genes were induced independently from FIT by conditions causing iron deficiency. Taken together, BHLH038, BHLH039, BHLH100 and BHLH101 function differently from FIT and may be involved in mediating a signal related to iron deficiency-induced stress and/or internal iron homeostasis.

关键词： bHLH basic helix-loop-helix Fer-like iron-deficiency induced transcription factor (FIT) iron acquisition iron uptake split root transcription factor

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Generation of a Twist1 conditional null allele in the mouse

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GENESIS 2007年第9期45卷 588-592页

作者： Chen, You-Tzung Akinwunmi, Peter O. Deng, Jian Min Tam, Oliver H. Behringer, Richard R. Univ Texas MD Anderson Canc Ctr Dept Mol Genet Houston TX 77030 USA

Twist1 is the mouse ortholog of TWIST1, the human gene mutated in Saethre-Chotzen syndrome. Previously, a Twist1 null allele was generated by gene targeting in mouse embryonic stem cells. Twist1 heterozygous mice develop polydactyly and a craniofacial phenotype similar to Saethre-Chotzen patients. Mice homozygous for the Twist1 null allele die around embryonic day 11.5 (E11.5) with cranial neural tube closure and vascular defects, hindering in vivo studies of Twist1 function at later stages of development. Here, we report the generation of a Twist1 conditional null allele in mice that functions like a wild-type allele but can be converted to a null allele upon Cre-mediated recombination.

关键词： mouse conditional allele Twist1 Cre/loxP basic helix-loop-helix

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Target genes for OBP3, a Dof transcription factor, include novel basic helix-loop-helix domain proteins inducible by salicylic acid

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PLANT JOURNAL 2003年第3期35卷 362-372页

作者： Kang, HG Foley, RC Oñate-Sánchez, L Lin, CGT Singh, KB Univ Calif Los Angeles Dept Mol Cell & Dev Biol Los Angeles CA 90095 USA CSIRO Plant Ind Wembley WA 6913 Australia

Overexpression of a salicylic-acid (SA)-inducible Arabidopsis DNA binding with one finger (Dof) transcription factor, called OBF-binding protein 3 (OBP3;AtDof3.6), has previously been shown to result in growth defects. In this study, suppressive subtraction hybridization (SSH) was used to isolate genes induced in an OBP3-overexpression line and several putative clones, called OBP3-responsive genes (ORGs), were isolated. The link with the induced expression levels of these genes and OBP3 overexpression was confirmed by analysing additional OBP3-overexpression lines. ORG1 through ORG4 are novel genes, while ORG5 is an extensin gene, AtExt1 . While ORG4 has no similarity with other proteins in the database, ORG1 has weak similarity in different regions of the predicted protein with CDC2 and fibrillin. ORG2 and ORG3 share 80% overall identity in their deduced amino acid sequences and contain a basic helix-loop-helix DNA-binding domain, suggesting that ORG2 and ORG3 may be transcription factors. The expression of the ORG1, ORG2 and ORG3 genes was co-regulated under all conditions examined including upregulation by SA and downregulation by jasmonic acid (JA). Fifteen OBP3-silenced lines were generated to further explore the function of OBP3. Although there were no visible phenotypic changes in any of these lines, the expression of ORG1, ORG2 and ORG3 was reduced. Among the ORG genes, ORG1, ORG2 and ORG3 contained the highest number of potential Dof-binding sites in the promoter region, and their expression was significantly increased within 3 h after induction of OBP3 expression using an inducible promoter system, and closely reflected the expression levels of the exogenous OBP3 protein. The results from the gain-of-function and loss-of-function experiments suggest that the ORG1, ORG2 and ORG3 genes are direct target genes of OBP3.

关键词： Dof basic helix-loop-helix salicylic acid jasmonic acid AtDof3.6

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Phylogenetic analysis of plant basic helix-loop-helix proteins

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JOURNAL OF MOLECULAR EVOLUTION 2003年第6期56卷 742-750页

作者： Buck, MJ Atchley, WR N Carolina State Univ Dept Genet Raleigh NC 27695 USA N Carolina State Univ Ctr Computat Biol Raleigh NC 27695 USA

The basic helix-loop-helix (bHLH) family of proteins is a group of functionally diverse transcription factors found in both plants and animals. These proteins evolved early in eukaryotic cells before the split of animals and plants, but appear to function in 'plant-specific' or 'animal-specific' processes. In animals bHLH proteins are involved in regulation of a wide variety of essential developmental processes. On the contrary, bHLH proteins have not been extensively studied in plants. Those that have been characterized function in anthocyanin biosynthesis, phytochrome signaling, globulin expression, fruit dehiscence, carpel and epidermal development. We have identified 118 different bHLH genes in the completely sequenced Arabidopsis thaliana genome and 131 bHLH genes in the rice genome. Here we report a phylogenetic analysis of these genes, including 46 genes from other plant species and a classification of these proteins into 15 distinct plant clades. Results imply a polyphyletic origin for the plant bHLH proteins related only by their bHLH DNA binding motif. We suggest that plant bHLH proteins are under weaker selective constraints than their animal counterparts and that lineage specific expansions and subfunctionalization have fashioned regulatory proteins for plant specific functions.

关键词： basic helix-loop-helix Arabidopsis thaliana rice phylogeny transcription factors G-box R genes E-box genome searching blast search

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Isolation and characterization of IRO2, a novel iron-regulated bHLH transcription factor in graminaceous plants

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JOURNAL OF EXPERIMENTAL BOTANY 2006年第11期57卷 2867-2878页

作者： Ogo, Yuko Itai, Reiko Nakanishi Nakanishi, Hiromi Inoue, Haruhiko Kobayashi, Takanori Suzuki, Motofumi Takahashi, Michiko Mori, Satoshi Nishizawa, Naoko K. Univ Tokyo Grad Sch Agr & Life Sci Bunkyo Ku Tokyo 1138657 Japan JST CREST Tokyo Japan

To clarify the molecular mechanism that regulates iron (Fe) acquisition in graminaceous plants, a time-course analysis of gene expression during Fe deficiency stress was conducted using a rice 22K oligo-DNA microarray. Twenty-one genes for proteins that function in gene regulation were induced by Fe deficiency. Of these genes, a putative basic helix-loop-helix (bHLH) transcription factor gene, named OsIRO2, was strongly expressed in both roots and shoots during Fe deficiency stress. The expression of OsIRO2 was induced exclusively by Fe deficiency, and not by deficiencies in other metals. Expression of the barley HvIRO2 gene, which is a homologue of OsIRO2, was also induced by Fe deficiency. An in silico search revealed that IRO2 is highly conserved among graminaceous plants, which include wheat, sorghum, and maize. The cyclic amplification and selection of targets (CASTing) technique revealed that OsIRO2 bound preferentially to the sequence 5'-ACCACGTGGTTTT-3', and the electrophoretic mobility shift assay revealed 5'-CACGTGG-3' as the core sequence for OsIRO2 binding. Sequences similar to the OsIRO2-binding sequence were found upstream of several genes that are involved in Fe acquisition, such as OsNAS1, OsNAS3, OsIRT1, OsFDH, OsAPT1, and IDS3. The core sequence of the OsIRO2-binding sequence occurred more frequently in the upstream regions of Fe deficiency-inducible genes than in the corresponding regions of non-inducible genes. These results suggest that IRO2 is involved in the regulation of gene expression under Fe-deficient conditions.

关键词： basic helix-loop-helix iron deficiency microarray mugineic acids phytosiderophore rice transcription factor

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