Transcriptional activation domains of the single-minded bHLH protein are required for CNS midline cell development.
ABSTRACT The single-minded gene functions as a master developmental regulator within the midline cell lineage of the embryonic central nervous system of Drosophila melanogaster. Genetic experiments suggest that Single-minded can function as a transcriptional activator. Regions of the Single-minded protein were fused to the DNA binding domain of the mammalian transcription factor Sp1 and shown to activate transcription from a reporter gene linked to Sp1 binding sites. Three independent activation domains were identified in the carboxy terminal region of Single-minded that include areas rich in serine, threonine, glutamine and proline residues. Germ line transformation experiments indicate that the carboxy terminal activation domains, the PAS dimerization domain, and the putative DNA binding basic domain of Single-minded are required for expression of CNS midline genes in vivo. These results define in vivo a functional activation domain within Single-minded and suggest a model in which Single-minded activates transcription through a direct interaction with promoter elements of CNS midline genes.
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ABSTRACT: The Drosophila single-minded and trachealess bHLH-PAS genes control transcription and development of the CNS midline cell lineage and tracheal tubules, respectively. We show that Single-minded and Trachealess activate transcription by forming dimers with the Drosophila Tango protein that is an orthologue of the mammalian Arnt protein. Both cell culture and in vivo studies show that a DNA enhancer element acts as a binding site for both Single-minded::Tango and Trachealess::Tango heterodimers and functions in controlling CNS midline and tracheal transcription. Isolation and analysis of tango mutants reveal CNS midline and tracheal defects, and gene dosage studies demonstrate in vivo interactions between single-minded::tango and trachealess::tango. These experiments support the existence of an evolutionarily conserved, functionally diverse bHLH-PAS protein regulatory system.Development 12/1997; 124(22):4571-82. · 6.21 Impact Factor
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ABSTRACT: The single-minded (sim) gene encodes a transcriptional regulator that functions as a key determinant of central nervous system (CNS) midline development in Drosophila. We report here the identification of two murine homologs of sim, Sim1 and Sim2, whose products show a high degree of sequence conservation with Drosophila SIM in their amino-terminal halves, with each containing a basic helix-loop-helix domain as well as a PAS domain. Sim1 maps to the proximal region of mouse chromosome 10, whereas Sim2 maps to a portion of the distal end of chromosome 16 that is syntenic to the Down syndrome critical region of human chromosome 21. Recent exon-trapping studies have identified in the critical region several exons of a human sim homolog which appears to be the homolog of murine Sim2; this has led to the hypothesis that increased dosage of this sim homolog in cases of trisomy 21 might be a causal factor in the pathogenesis of Down syndrome. We have examined the expression patterns of the Sim genes during embryogenesis. Both genes are expressed in dynamic and selective fashion in specific neuromeric compartments of the developing forebrain, and the expression pattern of Sim2 provides evidence for early regionalization of the diencephalon prior to any overt morphological differentiation in this region. Outside the CNS, Sim1 is expressed in mesodermal and endodermal tissues, including developing somites, mesonephric duct, and foregut. Sim2 is expressed in facial and trunk cartilage, as well as trunk muscles. Both murine Sim genes are also expressed in the developing kidney. Our data suggest that the Sim genes play roles in directing the regionalization of tissues where they are expressed. Moreover, the expression pattern documented for Sim2 may provide insights into its potential roles in Down syndrome.Molecular and Cellular Neuroscience 02/1996; 7(1):1-16. · 3.84 Impact Factor
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ABSTRACT: Central nervous system midline cells constitute a discrete group of Drosophila embryonic cells with numerous functional and developmental roles. Corresponding to their separate identity, the midline cells display patterns of gene expression distinct from the lateral central nervous system. A conserved 5 base pair sequence (ACGTG) was identified in central nervous system midline transcriptional enhancers of three genes. Germ-line transformation experiments indicate that this motif forms the core of an element required for central nervous system midline transcription. The central nervous system midline element is related to the mammalian xenobiotic response element, which regulates transcription of genes that metabolize aromatic hydrocarbons. These data suggest a model whereby related basic-helix-loop-helix-PAS proteins interact with asymmetric E-box-like target sequences to control these disparate processes.Development 01/1995; 120(12):3563-9. · 6.21 Impact Factor