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3582 Publications

Showing 3461-3470 of 3582 results
03/01/97 | RNase MRP correctly cleaves a novel R loop at the mitochondrial DNA leading-strand origin of replication.
Clayton DA, Lee DY
Genes & Development. 1997 Mar;11(5):582-92

The precursor primer RNA for mammalian mitochondrial DNA leading-strand replication remains as a persistent R loop formed during transcription through the mitochondrial DNA control region. We have examined model R loops, which exist in a novel and physiologically accurate preprimer conformation, as potential substrates for mammalian RNase mitochondrial RNA processing (MRP). Mouse RNase MRP accurately cleaves an R loop containing the mouse mitochondrial DNA origin. The multiple cleavage sites on the R-loop substrate match the priming sites observed in vivo, suggesting that RNase MRP alone is capable of generating virtually all of the leading-strand replication primers.

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01/01/97 | Determining aphid taxonomic affinities and life cycles with molecular data: a case study of the tribe Cerataphidini (Hormaphididae: Aphidoidea: Hemiptera)
David Stern , Shigeyuki Aoki , Shigeyuki Kurosu
Systematic Entomology. 01/1997;22(1):81-96. doi: 10.1046/j.1365-3113.1997.d01-20.x

Aphid taxonomy is often frustrated by the host alternation and extensive polyphenism displayed by many species. Here we examine the utility of using molecular data to assist in life cycle and taxonomic determination. We found that a relatively small amount of DNA sequence data can greatly assist in these tasks. Molecular data have identified the synonymy of five species: Tuberaphis plicator (Noordam) is a junior synonym of T.takenouchii (Takahashi), T.taiwana (Takahashi) is a junior synonym of T.coreana Takahashi, Hamiltonaphis styraci (Matsumura) is transferred to Tuberaphis Takahashi, Astegopteryx roepkei Hille Ris Lambers is transferred to Ceratoglyphina van der Goot, and A.vandermeermohri Hille Ris Lambers is transferred to Cerataphis Lichtenstein. We have elucidated the complete life cycles of five species: A.basalis (van der Goot) alternates between Styrax benzoin and bamboos, Ceratoglyphina bambusae van der Goot alternates between S.benzoin and bamboos, Pseudoregma sundanica (van der Goot) alternates between S.paralleloneura and Zingiberaceae, T.coreana alternates between S.formosana and Loranthaceae, and T.takenouchii alternates between S.japonica and Loranthaceae. In all cases the molecular data agreed with available morphological data. This analysis demonstrates the utility of DNA sequence comparisons for elucidating complex life cycles and the taxonomy of difficult insect groups.

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01/01/97 | Retinal morphogenesis in Drosophila: hints from an eye-specific decapentaplegic allele.
Chanut F, Heberlein U
Developmental Genetics. 1997;20(3):197-207. doi: 10.1002/(SICI)1520-6408(1997)20:3<197::AID-DVG3>3.0.CO;2-2

Decapentaplegic (dpp) regulates many aspects of imaginal disc growth and patterning in Drosophila. We have analyzed the phenotype of an eye-specific dpp allele, dppblk, which causes a reduction in the size of the retina due to a loss of ventral ommatidia. Prior to the onset of differentiation, dppblk eye discs are normal regarding size, shape, and ability to express dorsal and ventral markers. However, expression of a dpp-lacZ reporter is reduced at the ventral margin. Additional dorsoventral asymmetry appears during retinal differentiation: the morphogenetic furrow (MF) initiates normally at the posterior tip of the disc, but fails to propagate into the ventral epithelium. This defect can be rescued by increasing dpp expression along the ventral margin by local removal of patched function. We propose that the primary defect in dppblk is an inability to activate dpp expression properly at the ventral margin. This has two consequences: it prevents initiation from the ventral margin, and it renders the ventral epithelium unresponsive to differentiation signals emanating from the MF.

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Morphogenesis in the Drosophila retina initiates at the posterior margin of the eye imaginal disc by an unknown mechanism. Upon initiation, a wave of differentiation, its forward edge marked by the morphogenetic furrow (MF), proceeds anteriorly across the disc. Progression of the MF is driven by hedgehog (hh), expressed by differentiating photoreceptor cells. The TGF-beta homolog encoded by decapentaplegic (dpp) is expressed at the disc's posterior margin prior to initiation and in the furrow, under the control of hh, during MF progression. While dpp has been implicated in eye disc growth and morphogenesis, its precise role in retinal differentiation has not been determined. To address the role of dpp in initiation and progression of retinal differentiation we analyzed the consequences of reduced and increased dpp function during eye development. We find that dpp is not only required for normal MF initiation, but is sufficient to induce ectopic initiation of differentiation. Inappropriate initiation is normally inhibited by wingless (wg). Loss of dpp function is accompanied by expansion of wg expression, while increased dpp function leads to loss of wg transcription. In addition, dpp is required to maintain, and sufficient to induce, its own expression along the disc's margins. We postulate that dpp autoregulation and dpp-mediated inhibition of wg expression are required for the coordinated regulation of furrow initiation and progression. Finally, we show that in the later stages of retinal differentiation, reduction of dpp function leads to an arrest in MF progression.

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Baker Lab
12/13/96 | Control of male sexual behavior and sexual orientation in Drosophila by the fruitless gene.
Baker B, Ryner L, Goodwin S, Castrillon D, Anand A, Villella A, Hall J, Taylor B, Wasserman S
Cell. 1996 Dec 13;87(6):1079-89

Sexual orientation and courtship behavior in Drosophila are regulated by fruitless (fru), the first gene in a branch of the sex-determination hierarchy functioning specifically in the central nervous system (CNS). The phenotypes of new fru mutants encompass nearly all aspects of male sexual behavior. Alternative splicing of fru transcripts produces sex-specific proteins belonging to the BTB-ZF family of transcriptional regulators. The sex-specific fru products are produced in only about 500 of the 10(5) neurons that comprise the CNS. The properties of neurons expressing these fru products suggest that fru specifies the fates or activities of neurons that carry out higher order control functions to elicit and coordinate the activities comprising male courtship behavior.

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12/01/96 | GFP tagging of budding yeast chromosomes reveals that protein-protein interactions can mediate sister chromatid cohesion.
Straight AF, Belmont AS, Robinett CC, Murray AW
Current Biology. 1996 Dec 1;6(12):1599-608

Precise control of sister chromatid separation is essential for the accurate transmission of genetic information. Sister chromatids must remain linked to each other from the time of DNA replication until the onset of chromosome segregation, when the linkage must be promptly dissolved. Recent studies suggest that the machinery that is responsible for the destruction of mitotic cyclins also degrades proteins that play a role in maintaining sister chromatid linkage, and that this machinery is regulated by the spindle-assembly checkpoint. Studies on these problems in budding yeast are hampered by the inability to resolve its chromosomes by light or electron microscopy.

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12/01/96 | In vivo localization of DNA sequences and visualization of large-scale chromatin organization using lac operator/repressor recognition.
Robinett CC, Straight A, Li G, Willhelm C, Sudlow G, Murray A, Belmont AS
The Journal of Cell Biology. 1996 Dec;135(6 Pt 2):1685-700

We report a new method for in situ localization of DNA sequences that allows excellent preservation of nuclear and chromosomal ultrastructure and direct, in vivo observations. 256 direct repeats of the lac operator were added to vector constructs used for transfection and served as a tag for labeling by lac repressor. This system was first characterized by visualization of chromosome homogeneously staining regions (HSRs) produced by gene amplification using a dihydrofolate reductase (DHFR) expression vector with methotrexate selection. Using electron microscopy, most HSRs showed approximately 100-nm fibers, as described previously for the bulk, large-scale chromatin organization in these cells, and by light microscopy, distinct, large-scale chromatin fibers could be traced in vivo up to 5 microns in length. Subsequent experiments demonstrated the potential for more general applications of this labeling technology. Single and multiple copies of the integrated vector could be detected in living CHO cells before gene amplification, and detection of a single 256 lac operator repeat and its stability during mitosis was demonstrated by its targeted insertion into budding yeast cells by homologous recombination. In both CHO cells and yeast, use of the green fluorescent protein-lac repressor protein allowed extended, in vivo observations of the operator-tagged chromosomal DNA. Future applications of this technology should facilitate structural, functional, and genetic analysis of chromatin organization, chromosome dynamics, and nuclear architecture.

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Many developing insect neurones pass through a phase when they respond to nitric oxide (NO) by producing cyclic GMP. Studies on identified grasshopper motoneurones show that this NO sensitivity appears after the growth cone has arrived at its target but before it has started to send out branches. NO sensitivity typically ends as synaptogenesis is nearing completion. Data from interneurones and sensory neurones are also consistent with the hypothesis that NO sensitivity appears as a developing neurone changes from axonal outgrowth to maturation and synaptogenesis. Cyclic GMP likely constitutes part of a retrograde signalling pathway between a neurone and its synaptic partner. NO sensitivity also appears in some mature neurones at times when they may be undergoing synaptic rearrangement. Comparative studies on other insects indicate that the association between an NO-sensitive guanylate cyclase and synaptogenesis is an ancient one, as evidenced by its presence in both ancient and more recently evolved insect groups.

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Baker Lab
09/12/96 | The dosage compensation system of Drosophila is co-opted by newly evolved X chromosomes.
Marin I, Franke A, Bashaw GJ, Baker BS
Nature. 1996 Sep 12;383(6596):160-3. doi: 10.1038/383160a0

In species where males and females differ in number of sex chromosomes, the expression of sex-linked genes is equalized by a process known as dosage compensation. In Drosophila melanogaster, dosage compensation is mediated by the binding of the products of the male-specific lethal (msl) genes to the single male X chromosome. Here we report that the sex- and chromosome-specific binding of three of the msl proteins (MSLs) occurs in other drosophilid species, spanning four genera. Moreover, we show that MSL binding correlates with the evolution of the sex chromosomes: in species that have acquired a second X chromosome arm because of an X-autosome translocation, we observe binding of the MSLs to the 'new' (previously autosomal) arm of the X chromosome, only when its homologue has degenerated. Moreover, in Drosophila miranda, a Y-autosome translocation has produced a new X chromosome (called neo-X), only some regions of which are dosage compensated. In this neo-X chromosome, the pattern of MSL binding correlates with the known pattern of dosage compensation.

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07/01/96 | Modal aproximation for the electromagnetic field of a near-field optical probe.
Grober RD, Rutherford T, Harris TD
Applied Optics. 1996 Jul 1;35(19):3488-95. doi: 10.1364/AO.35.003488

A formalism is given in which the optical field generated by a near-field optical aperture is described as an analytic expansion over a complete set of optical modes. This vectoral solution preserves the divergent behavior of the near field and the dipolar nature of the far field. Numerical calculation of the fields requires only evaluation of a well behaved, one-dimensional integral. The formalism is directly applicable to experiments in near-field scanning optical microscopy when relatively flat samples are evaluated.

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