Basic Helix (basic + helix)

Distribution by Scientific Domains

Selected Abstracts

Cath6, a bHLH atonal family proneural gene, negatively regulates neuronal differentiation in the retina

Fumi Kubo
Abstract Basic helix,loop,helix (bHLH) transcription factors play important roles in cell type specification and differentiation during the development of the nervous system. In this study, we identified a chicken homolog of Atonal 8/ath6 (Cath6) and examined its role in the developing retina. Unlike other Atonal-family proneural genes that induce neuronal differentiation, Cath6 was expressed in stem cell-like progenitor cells in the marginal region of the retina, and its overexpression inhibited neuronal differentiation. A Cath6 fused with a VP16 transactivation domain recapitulated the inhibitory effect of Cath6 on neuronal differentiation, indicating that Cath6 functions as a transcription activator. These results demonstrate that Cath6 constitutes a unique member of the Atonal-family of genes in that it acts as a negative regulator of neuronal differentiation. Developmental Dynamics 239:2492,2500, 2010. © 2010 Wiley-Liss, Inc. [source]

Relationship between delta-like and proneural bHLH genes during chick retinal development

Branden R. Nelson
Abstract Notch signaling in the retina maintains a pool of progenitor cells throughout retinogenesis. However, two Notch-ligands from the Delta-like gene family, Dll1 and Dll4, are present in the developing retina. To understand their relationship, we characterized Dll1 and Dll4 expression with respect to proliferating progenitor cells and newborn neurons in the chick retina. Dll4 matched the pattern of neural differentiation. By contrast, Dll1 was primarily expressed in progenitor cells. We compared Dll1 and Dll4 kinetic profiles with that of the transiently up-regulated cascade of proneural basic helix,loop,helix (bHLH) genes after synchronized progenitor cell differentiation, which suggested a potential role for Ascl1 in the regulation of Delta-like genes. Gain-of-function assays demonstrate that Ascl1 does influence Delta-like gene expression and Notch signaling activity. These data suggest that multiple sources of Notch signaling from newborn neurons and progenitors themselves coordinate retinal histogenesis. Developmental Dynamics 237:1565,1580, 2008. © 2008 Wiley-Liss, Inc. [source]

Muscle stem cells and model systems for their investigation

Nicolas Figeac
Abstract Stem cells are characterized by their clonal ability both to generate differentiated progeny and to undergo self-renewal. Studies of adult mammalian organs have revealed stem cells in practically every tissue. In the adult skeletal muscle, satellite cells are the primary muscle stem cells, responsible for postnatal muscle growth, hypertrophy, and regeneration. In the past decade, several molecular markers have been found that identify satellite cells in quiescent and activated states. However, despite their prime importance, surprisingly little is known about the biology of satellite cells, as their analysis was for a long time hampered by a lack of genetically amenable experimental models where their properties can be dissected. Here, we review how the embryonic origin of satellite cells was discovered using chick and mouse model systems and discuss how cells from other sources can contribute to muscle regeneration. We present evidence for evolutionarily conserved properties of muscle stem cells and their identification in lower vertebrates and in the fruit fly. In Drosophila, muscle stem cells called adult muscle precursors (AMP) can be identified in embryos and in larvae by persistent expression of a myogenic basic helix,loop,helix factor Twist. AMP cells play a crucial role in the Drosophila life cycle, allowing de novo formation and regeneration of adult musculature during metamorphosis. Based on the premise that AMPs represent satellite-like cells of the fruit fly, important insight into the biology of vertebrate muscle stem cells can be gained from genetic analysis in Drosophila. Developmental Dynamics 236:3332,3342, 2007. © 2007 Wiley-Liss, Inc. [source]

Characterization of TROY-expressing cells in the developing and postnatal CNS: the possible role in neuronal and glial cell development

Tomoko Hisaoka
Abstract A member of the tumor necrosis factor receptor superfamily, TROY, is expressed in the CNS of embryonic and adult mice. In the present study, we characterized TROY-expressing cells in the embryonic and postnatal forebrain. In the early embryonic forebrain, TROY was highly expressed in nestin-positive neuroepithelial cells and radial glial cells, but not in microtubule-associated protein 2-positive postmitotic neurons. During the late embryonic and postnatal development, expression of TROY was observed in radial glial cells and astrocytes, whereas its expression was not detected in neuronal lineage cells. In addition, TROY was exclusively expressed in Musashi-1-positive multipotent/glial progenitors in the postnatal subventricular zone. To investigate the functions of TROY in neural development, we overexpressed TROY in PC12 cells and established stably expressing cell clones. As expected, the signals from overexpressed TROY were constitutively transduced via the activation of the nuclear factor-,B and the c-Jun N-terminal kinase pathways in such clones. In addition, upregulation of negative basic helix,loop,helix transcription factors, HES-5 and Id2 proteins, was observed in the TROY-overexpressing clones. Interestingly, the overexpression of TROY in PC12 cells strongly inhibited nerve growth factor-induced neurite outgrowth with reduction of some markers of differentiated neurons, such as neurofilament 150 kDa and neuron-specific ,-tubulin. These findings suggest that the signaling from TROY regulates neuronal differentiation at least in part. [source]

Spectroscopic and DNA-binding characterization of the isolated heme-bound basic helix,loop,helix-PAS-A domain of neuronal PAS protein 2 (NPAS2), a transcription activator protein associated with circadian rhythms

FEBS JOURNAL, Issue 11 2006
Yuji Mukaiyama
Neuronal PAS domain protein 2 (NPAS2) is a circadian rhythm-associated transcription factor with two heme-binding sites on two PAS domains. In the present study, we compared the optical absorption spectra, resonance Raman spectra, heme-binding kinetics and DNA-binding characteristics of the isolated fragment containing the N-terminal basic helix,loop,helix (bHLH) of the first PAS (PAS-A) domain of NPAS2 with those of the PAS-A domain alone. We found that the heme-bound bHLH-PAS-A domain mainly exists as a dimer in solution. The Soret absorption peak of the Fe(III) complex for bHLH-PAS-A (421 nm) was located at a wavelength 9 nm higher than for isolated PAS-A (412 nm). The axial ligand trans to CO in bHLH-PAS-A appears to be His, based on the resonance Raman spectra. In addition, the rate constant for heme association with apo-bHLH-PAS (3.3 × 107 mol,1·s,1) was more than two orders of magnitude higher than for association with apo-PAS-A (< 105 mol,1·s,1). These results suggest that the bHLH domain assists in stable heme binding to NPAS2. Both optical and resonance Raman spectra indicated that the Fe(II),NO heme complex is five-coordinated. Using the quartz-crystal microbalance method, we found that the bHLH-PAS-A domain binds specifically to the E-box DNA sequence in the presence, but not in the absence, of heme. On the basis of these results, we discuss the mode of heme binding by bHLH-PAS-A and its potential role in regulating DNA binding. [source]

Evolution and phylogenetic relationships of APSES proteins from Hemiascomycetes

Bernardo Ramírez-Zavala
Abstract Available complete genomic sequences of hemiascomycetous yeast species were analysed in order to identify the APSES protein family, which belongs to transcriptional factors of the basic helix,loop,helix (bHLH) class. Phylogenetic analyses of the amino acid sequences revealed that a similar set of proteins were present in all yeast species studied. The genome duplication event of Saccharomycetales allows the acquisition of complementary functions between the APSES proteins. Putative ancestors, such as Ashbya gossypii, the Kluyveromyces group and filamentous fungi, only have one APSES protein. Conserved gene order relationships allow the possibility of tracing the evolution of this family and the detection of duplication events. Multiple alignments revealed strict conservation of the APSES motif, although other regions of the APSES proteins were diversified. This review focuses on the evolution of the gene family of APSES proteins in related Hemiascomycetes species; the comparisons could shed light on the functional overlap of these proteins with regard to the regulation of morphogenetic processes and their involvement in the virulence of pathogenic microorganisms. [source]

A novel role of hippocalcin in bFGF-induced neurite outgrowth of H19-7 cells

Doo-Yi Oh
Abstract Hippocalcin is a Ca2+ -binding protein that is expressed mainly in pyramidal nerve cells of the hippocampus. However, its functions and mechanism in the brain remain unclear. To elucidate the role of hippocalcin, we used a conditionally immortalized hippocampal cell line (H19-7) and showed that bFGF treatment increased the expression of hippocalcin during bFGF-induced neurite outgrowth of H19-7 cells. Overexpression of hippocalcin dramatically elongated neurites and increased the expression of basic helix,loop,helix transcription factor, that is, NeuroD without bFGF stimulation. Treatment of the cells with hippocalcin siRNA completely blocked bFGF-induced neurite outgrowth and NeuroD expression. bFGF stimulation resulted in activation of phospholipase C,, (PLC-,) and an increased level of intracellular Ca2+. Hippocalcin expression by bFGF stimulation was fully blocked by both the PLC-, inhibitor U73122 and BAPTA-AM, a chelator of intracellular Ca2+, suggesting that hippocalcin expression by bFGF is dependent on PLC-, and Ca2+. Moreover, both U73122 and BAPTA-AM completely blocked bFGF-induced neurite outgrowth and NeuroD expression. Taken together, these results suggest for the first time that bFGF induces hippocalcin expression in H19-7 cells through PLC-, activation, which leads to neurite outgrowth. © 2008 Wiley-Liss, Inc. [source]

Putting numbers on the network connections

BIOESSAYS, Issue 8 2007
Gary D. Stormo
DNA,protein interactions are fundamental to many biological processes, including the regulation of gene expression. Determining the binding affinities of transcription factors (TFs) to different DNA sequences allows the quantitative modeling of transcriptional regulatory networks and has been a significant technical challenge in molecular biology for many years. A recent paper by Maerkl and Quake1 demonstrated the use of microfluidic technology for the analysis of DNA,protein interactions. An array of short DNA sequences was spotted onto a glass slide, which was then covered with a microfluidic device allowing each spot to be within a chamber into which the flow of materials was controlled by valves. By trapping the DNA,protein complexes on the surface and measuring their concentrations microscopically, they could determine the binding affinity to a large number of DNA sequences that were varied systematically. They studied four TFs from the basic helix,loop,helix family of proteins, all of which bind to E-box sites with the consensus CAnnTG (where "n" can be any base), and showed that variations in affinity for different sites allows each TF to regulate different genes. BioEssays 29:717,721, 2007. © 2007 Wiley Periodicals, Inc. [source]

A twisted hand: bHLH protein phosphorylation and dimerization regulate limb development

BIOESSAYS, Issue 11 2005
Juanliang Cai
Saethre-Chotzen syndrome (SCS), a human autosomal dominant condition with limb defects and craniosynostosis, is caused by haploinsufficiency of TWIST1, a basic helix,loop,helix (bHLH) transcription factor. Until recently, the molecular pathogenesis of the limb defects in SCS has not been well understood. Now, Firulli et al.1 show in mouse and chick that ectopic expression of a related bHLH protein, Hand2, results in phenocopies of the limb defects caused by Twist1 loss-of-function mutations. These two proteins interact in a dosage-dependent antagonistic manner, and both can be regulated through phosphorylation at conserved helix I amino acid residues. These findings provide an important link between the misregulation of Twist1 dimerization and the limb phenotypes observed in SCS. BioEssays 27:1102,1106, 2005. © 2005 Wiley Periodicals, Inc. [source]

Design and Characterisation of an Artificial DNA-Binding Cytochrome

CHEMBIOCHEM, Issue 7 2004
D. Dafydd Jones Dr.
Abstract We aim to design novel proteins that link specific biochemical binding events, such as DNA recognition, with electron transfer functionality. We want these proteins to form the basis of new molecules that can be used for templated assembly of conducting cofactors or for thermodynamically linking DNA binding with cofactor chemistry for nanodevice applications. The first examples of our new proteins recruit the DNA-binding basic helix region of the leucine zipper protein GCN4. This basic helix region was attached to the N and C termini of cytochrome b562(cyt b562) to produce new, monomeric, multifunctional polypeptides. We have fully characterised the DNA and haem-binding properties of these proteins, which is a prerequisite for future application of the new molecules. Attachment of a single basic helix of GCN4 to either the N or C terminus of the cytochrome does not result in specific DNA binding but the presence of DNA-binding domains at both termini converts the cytochrome into a specific DNA-binding protein. Upon binding haem, this chimeric protein attains the spectral characteristics of wild-type cyt b562. The three forms of the protein, apo, oxidised holo and reduced holo, all bind the designed (ATGAcgATGA) target DNA sequence with a dissociation constant, KD, of approximately 90 nM. The protein has a lower affinity (KDca. 370 nM) for the wild-type GCN4 recognition sequence (ATGAcTCAT). The presence of only half the consensus DNA sequence (ATGAcgGGCC) shifts the KDvalue to more than 2500 nM and the chimera does not bind specifically to DNA sequences with no target recognition sites. Ultracentrifugation revealed that the holoprotein,DNA complex is formed with a 1:1 stoichiometry, which indicates that a higher-order protein aggregate is not responsible for DNA binding. Mutagenesis of a loop linking helices 2 and 3 of the cytochrome results in a chimera with a haem-dependent DNA binding affinity. This is the first demonstration that binding of a haem group to a designed monomeric protein can allosterically modulate the DNA binding affinity. [source]