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S Crews

Publications and source records attributed to S Crews.

18 recordsLinked to original sources
PubMed1998

Specification of the Drosophila CNS midline cell lineage: direct control of single-minded transcription by dorsal/ventral patterning genes.

The Drosophila CNS consists of a bilaterally symmetric group of neurons separated by a discrete group of CNS midline cells. The specification of the CNS midline cell lineage requires transcription of the single-minded gene. Genetic evidence suggests that a group of transcription factors, including Dorsal, Snail, Twist, and Daughterless:: Scute, is required for initial single-minded transcription. Comparison of the DNA sequences of the single-minded gene regulatory regions between two Drosophila species reveals conserved sequence elements. Biochemical studies using purified proteins indicate that a number of these conserved sequences represent binding sites for Dorsal, Snail, and Twist. In vitro mutagenesis combined with germline transformation indicates that these binding sites are required in vivo for single-minded mesectodermal transcription. These results show that single-minded transcription and, thus, CNS midline specification is directly controlled by dorsal/ventral patterning transcription factors. They also suggest a model in which multiple transcriptional activators function in a cooperative, concentration-dependent mode in combination with a transcriptional repressor to restrict single-minded transcription to the CNS midline precursor cells.

Amino Acid Sequence↗
PubMed1997

The Drosophila tango gene encodes a bHLH-PAS protein that is orthologous to mammalian Arnt and controls CNS midline and tracheal development.

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.

Amino Acid Sequence↗
PubMed1996

Expression patterns of two murine homologs of Drosophila single-minded suggest possible roles in embryonic patterning and in the pathogenesis of Down syndrome.

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.

Amino Acid Sequence↗
PubMed1992

Drosophila single-minded gene and the molecular genetics of CNS midline development.

Our goal is to understand the molecular mechanisms that govern the formation of the central nervous system. In particular, we have focused on the development of a small group of neurons and glia that lie along the midline of the Drosophila CNS. These midline cells possess a number of unique attributes which make them particularly amenable to molecular, cellular, and genetic examinations of nervous system formation and function. In addition, the midline cells exhibit distinctive ontogeny, morphology, anatomical position, and patterns of gene expression which suggest that they may provide unique functions to the developing CNS. The single-minded gene encodes a nuclear protein which is specifically expressed in the midline cells and has been shown to play a crucial role in midline cell development and CNS formation. Genetic experiments reveal that sim is required for the expression of many CNS midline genes which are thought to be involved in the proper differentiation of these cells. In order to identify additional genes which are expressed in some or all of the midline cells at different developmental stages, a technique known as enhancer trap screening was employed. This screen led to the identification of a large number of potential genes which exhibit various midline expression patterns and may be involved in discrete aspects of midline cell development. Further molecular, genetic, and biochemical analyses of sim and several of the enhancer trap lines are being pursued. This should permit elucidation of the genetic hierarchy which acts in the specification, differentiation, and function of these CNS midline cells.

Animals↗
PubMed1983

Oncogenes and chromosomes.

Two tumors of B lymphocytes, murine plasmacytomas and human Burkitt's lymphoma, display characteristic chromosomal translocations. Molecular cloning studies have shown that these tumors have translocated an oncogene, called C'MYC, into the antibody gene locus. This oncogene translocation probably contributes to but is not sufficient for the occurrence of these tumors.

Animals↗
PubMed1982

Mouse c-myc oncogene is located on chromosome 15 and translocated to chromosome 12 in plasmacytomas.

Hybridization studies with viral oncogene probes indicate that c-myc, the cellular gene homologous to the transforming gene of avian myelocytomatosis virus, resides on mouse chromosome 15 and in many plasmacytomas is translocated to the antibody heavy chain gene locus on chromosome 12. The transcriptional orientation of the translocated c-myc sequence is opposite the orientation of the adjacent C alpha gene that codes for the heavy chain of immunoglobulin A. The translocated c-myc sequence is not the same oncogene detected in urine plasmacytomas by the NIH-3T3 cell transformation assay.

Animals↗
PubMed1982

An immunoglobulin promoter region is unaltered by DNA rearrangement and somatic mutation during B-cell development.

The V1 gene encodes the heavy chain variable region of antibodies that bind to phosphorylcholine in the Balb/c mouse. V1 genes have been cloned from mouse sperm DNA, an IgM-producing tumor HPCM2 and an IgA-producing tumor M167. The transcription start site of the V1 gene has been mapped 63 +/- 1 base pairs from the coding sequence for both alpha and mu transcripts. Comparison of flanking DNA sequence 574 base pairs 5' to the V1 transcription start site in sperm, HPCM2 and M167 DNA reveals that sperm and HPCM2 sequences are completely identical in this region and the M167 sequence differs from them by a single base change. Although the coding region of the V1 gene has undergone a high (4%) rate of somatic mutation in M167 we demonstrate that the somatic mutation mechanism stops near the transcription start site. These results demonstrate that initiation of V1 gene transcription remains unchanged with respect to location and 5' sequences throughout B-cell development.

Animals↗
PubMed1982

Antibody and MHC genes.

The striking homology relationships, both in sequence and in general organizational features, among the genes encoding antibodies, transplantation antigens and beta 2-microglobulin suggest that these genes are members of a supergene family. It will be interesting to determine whether any of the regulatory strategies displayed by the antibody gene families will also be employed by the MHC gene families. Indeed, the recombinant DNA approach has given us profound insights into the organization and expression of antibody genes. These same techniques are now beginning to unravel the mysteries of the MHC complex. It is clear that the future will require a much closer collaboration between molecular biologists, cellular immunologists, and immunogeneticists to obtain the appropriate reagents and cell lines necessary to expand our understanding of the molecular biology and enzymology of gene expression in these fascinating systems.

Animals↗
PubMed1981

An immunoglobulin VH pseudogene.

In the course of studying the members of the T15 group of VH gene segments, some of which participate in the immune response to phosphorylcholine in the mouse, we identified a VH gene segment that contains three mutations preventing its expression. The mutations are an in-frame stop codon, a 4-base insertion which causes a termination codon to be shifted into the reading frame, and a modification of the recognition elements involved in the joining of VH and D gene segments during variable region formation. This pseudogene, which is 88-96% homologous to the other members of the T15 VH gene group, is probably of relatively recent origin and will presumably be deleted from the VH gene family eventually. We suggest that pseudogenes can only arise in multigene families and that the occurrence of pseudogenes will be a relatively frequent phenomenon in these families. Because the antibody gene families are made up of multiple gene elements, undergo two types of DNA rearrangements during differentiation, and employ several different RNA splicing mechanisms for expression, there are many different ways a particular antibody gene segment may become a pseudogene.

Animals↗
PubMed1978

Failure to detect "cap" structures in mitochondrial DNA-coded poly(A)-containing RNA from HeLa cells.

The structure of the 5'-termini has been investigated in mitochondrial DNA-coded poly(A)-containing RNA from HeLa cells. For this purpose, mitochondrial RNA isolated from cells labeled for 3 hours with [32P]orthophosphate in the presence of 20 microgram/ml camptothecin, and selected for poly(A) content by two passages through oligo(dT)-cellulose, was digested either with the nuclease P1 or with a mixture of RNases: the digestion products were then fractionated by two-dimensional electrophoresis. No "cap" structures were detected under conditions where the presence of such structures in one out of five to ten RNA molecules would have been recognized. It is, therefore, likely that "cap" structures are completely absent in HeLa cell mitochondrial poly(A)-containing RNA.

Base Sequence↗